A.O. Smith Burkay HW-300 Owner's manual

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PLACE THESE INSTRUCTIONS ADJACENT TO BOILER AND
NOTIFY OWNER TO KEEP FOR FUTURE REFERENCE
ADIVISIONOFA.O.SMITH CORPORATION
MCBEE, SC SEATTLE,WA
STRATFORD,ONTARIO
VELDHOVEN,THENETHERLANDS
www.hotwater.com
PART NO. 211683-000 REV.02
PRINTED IN U.S.A. 0905 SUPERSEDES PART NO'S, 210288-000 REV. 01 & 192356-000
GAS-FIREDCOMMERCIALCOPPERBOILERSFOR
HYDRONICHEATINGANDHOTWATER SUPPLY
•INSTALLATION • OPERATION •MAINTENANCE •LIMITED WARRANTY
•INDOOR ONLY
MODELS HW/HWB 300, 399, 420, 520, 610, 670
UP-FLOW MODELS
CAUTION
TEXTPRINTEDOROUTLINEDINRED CONTAINSINFORMATION
RELATIVE TO YOUR SAFETY. PLEASE READ THOROUGHLY
BEFOREUSINGAPPLIANCE.
WARNING: If the information in this manual
is not followed exactly, a fire or explosion
may result causing property damage,
personal injury or death.
— Do not store or use gasoline or other
flammable vapors and liquids in the
vicinity of this or any other appliance.
— WHAT TO DO IF YOU SMELL GAS
• Do not try to light any appliance.
• Do not touch any electrical switch;
do not use any phone in your
building.
• Immediately call your gas supplier
from a neighbor's phone. Follow the
gas supplier's instructions.
• Ifyoucannotreachyourgassupplier,
call the fire department.
— Installation and service must be
performed by a qualified installer,
service agency or the gas supplier.

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ROUGH-IN DIMENSIONS
TABLE 2, SPECIFICATIONS - CANADIAN MODELS ONLY
Maximum
Maximum I.A.S. Maximum Max. Heat Transfer Max. Heat Transfer
Model Type of Gas BTUH(KW) BTUH(KW) Heat Loss Load Surface Area (Sq. Ft.) Surface Area (Sq. Ft.)
HWB-300 Natural & Propane 300,000 (88) 247,200 (72) 210,120 (62) 1,410 (.41) 1,051 (.31)
HWB-399 Natural & Propane 399,000 (116) 322,790 (95) 274,371 (80) 1,829 (.54) 1,372 (.40)
HWB-420 Natural & Propane 420,000 (123) 344,400 (101) 292,740 (86) 1.952 (57) 1,464 (.43)
HWB-520 Natural & Propane 520,000 (152) 429,000 (126) 364,650 (107) 2,431 (.71) 1,823 (.53)
HWB-610 Natural 610,000 (179) 502,600 (147) 427,210 (125) 2,848 (.83) 2,136 (.61)
HWB-610 Propane 610,000 (179) 488,000 (143) 414,800 (121) 2,765 (.81) 2,074 (.61)
Ratings shown are for current modern heating system design. Where A.O. Smith boilers are connected to heavy, cast iron radiator systems or where unusual pick-up or
large size piping conditions exist, reduce ratings by 10%.
NOTE: To compensate for the effects of high altitude areas above 2000 feet, the input, output and heating load ratings should be reduced
approximately 4% for each 1000 feet above sea level.
EXTRAOPENING
FORTHERMOMETER
AND RELIEF VALVE
HW/HWB-520, 610
AND HW--670
HW/HWB-610
AND HW-670
NATURALGASONLY
TABLE 1 MODELS Prop. Nat.
HWB/ HWB/ HWB/ HWB/ HWB/ HWB/
HW-300 HW-399 HW-420 HW-520 HW-610/670 HW-610/670
AOverall height 65 (1651) 57-1/8 (1451) 57-1/8 (1451) 68-5/16 (1735) 67 (1702) 64-3/4 (1645)
BHeight to top of jacket 43-1/4 (1099) 45-1/8 (1146) 45-1/8 (1146) 56-1/4 (1429) 56-1/4 (1429) 56-1/4 (1429)
CFloor to center line water inlet 36 (914) 38-3/4 (984) 38-3/4 (984) 46 (1168) 46 (1168) 46 (1168)
DDiameter of jacket 25-1/4 (641) 27 (686) 27 (686) 27 (686) 27 (686) 27 (686)
EFloor to center line water outlet 12 (305) 12 (305) 12 (305) 12 (305) 12 (305) 12 (305)
FDraft diverter outlet diameter 8 (203) 10 (254) 10 (254) 10 (254) 12 (305) 12 (305)
GFloor to center line gas inlet 16-1/2 (419) 16-3/4 (425) 16-3/4 (425) 18 (457) 18 (457) 18 (457)
HOverall depth 29-5/8 (753) 31-1/2 (800) 31-1/2 (800) 36-1/2 (927) 36-1/2 (927) 36-1/2 (927)
JSupport height 9 (229) 9 (229) 9 (229) 9(229) 9 (229) 9 (229)
KWidth of control string (approx.) 14 (356) 14 (356) 14 (356) 11(279) 11 (279) 11 (279)
LPipe size of water inlet (NPT) 1-1/4 1-1/2 1-1/2 2 2 2
MPipe size of water outlet(NPT) 1-1/4 1-1/2 1-1/2 2 2 2
NPipe size of gas inlet (NPT) 3/4 1 1 1 1 1
PControl string plus 1/2 jacket dia. (approx.) 26-5/8 (676) 27-1/2(699) 27-1/2 (699) 24-1/2 (622) 24-1/2 (622) 24-1/2 (622)
QWater outlet to jacket 1 (25) 1 (25) 1 (25) 3-1/2 (89) 3-1/2 (89) 3-1/2 (89)
RWater inlet casting to center line of jacket 10-1/8 (257) 11-1/4 (286) 11-1/4 (286) 12 (305) 12 (305) 12 (305)
SHorizontal length between water inlet and outlet 5-3/8 (137) 5-1/2 (140) 5-1/2 (140) 5-3/4 (146) 5-3/4 (146) 5-3/4 (146)
TControl string from jacket 5 (127) 5 (127) 5 (127) 7 (178) 7 (178) 7 (178)
Approx. shipping weight lbs. (Kilograms) 240 (109) 291 (132) 291 (132) 361 (164) 361 (164) 361 (164)
NOTE: All dimensions in inches (millimeters) except pipe size which is NPT.
DIMENSIONSININCHES

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TABLE 3, RECOVERYCAPACITIES - CANADIAN MODELS ONLY
Input Temp. (C) 11 17 22 26 33 39 44 50 56 61 67 72 78
Model (Btu/Hr.) Rise (F) 20 30 40 50 60 70 80 90 100 110 120 130 140
HW-300 300,000 LPH 5,505 3,670 2,753 2,202 1,835 1,573 1,376 1,223 1,001 1,001 918 847 786
GPH 1,455 970 727 582 485 416 364 323 291 264 242 224 208
HW-399 399,000 LPH 7,322 4,882 3,661 2,929 2,441 2,092 1,831 1,627 1,464 1,331 1,220 1,127 1,046
GPH 1,935 1,290 967 774 645 553 484 430 387 352 322 298 276
HW-420 420,000 LPH 7,708 5,138 3,854 3,083 2,569 2,202 1,927 1,713 1,542 1,401 1,285 1,186 1,101
GPH 2,036 1,358 1,018 815 679 582 509 453 407 370 339 313 291
HW-520 520,000 LPH 9,543 6,362 4,771 3,817 3,181 2,727 2,386 2,121 1,909 1,735 1,590 1,468 1,363
GPH 2,521 1,681 1,261 1,008 840 720 630 560 504 458 420 388 360
HW-610 610,000 LPH 11,194 7,463 5,597 4,478 3,731 3,198 2,799 2,488 2,239 2,035 1,866 1,722 1,599
GPH 2,958 1,972 1,479 1,183 986 845 739 657 592 538 493 455 423

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CAUTION
TEXTPRINTEDOROUTLINEDINREDCONTAINSINFORMATIONRELATIVE
TOYOUR SAFETY. PLEASE READ THOROUGHLYBEFORE USING
APPLIANCE.
Detailedinstallationdiagramsareinthismanual. Thesediagramswillserve
to provide the installer with a reference for the materials and method of
pipingsuggested. ITISNECESSARYTHATALLWATERANDGASPIPING
ANDTHEELECTRICALWIRINGBEINSTALLEDANDCONNECTEDAS
SHOWNINTHEDIAGRAMS.
CHECKTHEDIAGRAMSTHOROUGHLYBEFORESTARTINGINSTALLATION
TOAVOIDPOSSIBLEERRORSANDTOMINIMIZETIMEANDMATERIALS
COST.
This design complies with the latest edition of ANSI Z21.13.
CSA4.9low-pressure boiler.
Particularattention should be given totheinstallation of thermometers at
FOREWORD
thelocationsindicatedinthediagramsas thesearenecessary forchecking
theoperation oftheboiler.
MAKESURETHEGASONWHICHTHEBOILERWILLOPERATEISTHE
SAMEASTHATSPECIFIEDONTHEUNITRATINGPLATE.
The boiler installation must conform to these instructions and the
requirementsof thelocalauthority havingjurisdiction.
Whererequiredbyauthorityhavingjurisdiction,theinstallationmustconform
to the Standard for Controls and Safety Devices for Automatically Fired
Boilers,ANSI/ASME CSD-1.
Inabsenceof localcode requirements,the boilerinstallation mustconform
tothe NationalFuel GasCode,ANSI Z223.1and/or CAN/CSAB-149.1-00
InstallationCodes.
Thesemanuals can be purchasedfrom the CSA International,8501 East
PleasantValleyRoad,Cleveland,OH 44131 or 178 Rexdale Boulevard,
Toronto,OntarioCanadaM9W1R3.
TABLE OF CONTENTS
START-UPANDOPERATINGINSTRUCTIONS .................................. 45
Filling And Venting...................................................................... 46
Pilot and Main Burner ................................................................. 46
Lighting Instructions ................................................................... 47-48
Pilot and Main Burner (Continued) ............................................. 49-51
Electronic Intermittent Pilot Ignition Control ................................. 51
Normal Operating Sequence With Honeywell S-8600H or
S-8610MIntermittent Ignition Control (I.I.D.) ............................... 52
High Altitude Installations ........................................................... 52
Thermal Balancer ....................................................................... 52
Coil High Limit Control (Protector Switch).................................. 52-53
Pressure Reducing Valve .......................................................... 53
Safety Flow Switch ................................................................... 53-54
Safety Relief Valve Maintenance............................................... 54
Replacement Parts ..................................................................... 54
REMOVALOFEXISTINGBOILERFROMACOMMON
VENTINGSYSTEM............................................................................ 54
GENERALMAINTENANCE ................................................................ 55
Relief Valve ................................................................................ 55
CLEANINGANDFLUSHINGINSTRUCTIONS .................................... 55
Internal Contaminants ................................................................. 55
Hot Water Supply Boilers - Preventive Maintenance ................ 55
Deliming ....................................................................................... 55-56
DelimingSolvents ....................................................................... 56
Heavy Lime Deposits ................................................................. 56
RemovingSilicate ....................................................................... 56
PRE-TROUBLE-SHOOTING ............................................................... 57
TROUBLE-SHOOTING....................................................................... 57-61
LIMITEDWARRANTY........................................................................ 62
PAGE
ROUGH-INDIMENSIONS ................................................................... 2-3
FOREWORD ...................................................................................... 4
INSTALLATIONINSTRUCTIONS ........................................................ 4
Required Ability .......................................................................... 4
Installation As Boiler Replacement ............................................. 4
Location ...................................................................................... 5
Air Requirements........................................................................ 5-6
Chemical Vapor Corrosion ......................................................... 6
Installation Clearances ............................................................... 6
Levelling...................................................................................... 6
System Connections .................................................................. 6-9
Gas Connections........................................................................ 9-11
Gas Pressure Regulators .......................................................... 11-12
Venting The Boiler - Standard Venting....................................... 12-14
Venting Maintenance - Standard Venting .................................. 15
Venting Sidewall (Optional) Power Vent System ...................... 15
Venting System .......................................................................... 15
Safety Relief Valves .................................................................. 15-16
Wiring Connections .................................................................... 16-31
Water Line Connections ............................................................. 32
Hard Water ................................................................................. 32
Tank Temperature Control .......................................................... 32-33
Low Water Cutoff ...................................................................... 33
Thermometers ............................................................................ 33
Drain Valve (Not Supplied) ......................................................... 33
Closed Water System ................................................................ 33
PipingDiagrams .......................................................................... 34-45
PAGE
INSTALLATION INSTRUCTIONS
REQUIREDABILITY
INSTALLATIONORSERVICE OFTHISBOILERREQUIRESABILITY
EQUIVALENT TO THAT OF A LICENSED TRADESMAN IN THE
FIELD INVOLVED. PLUMBING, AIR SUPPLY, VENTING, GAS
SUPPLYAND ELECTRICAL WORKARE REQUIRED.
INSTALLATIONAS BOILERREPLACEMENT
Installation as boiler replacement on an old system with large
water volume may experience condensation within the boiler on
cold starts. This condensing of water vapor in the combustion
area can be prevented if a portion of the system water flow is
diverted past the boiler to cause an increase in boiler temperature
rise.
With old systems where water temperature can be expected to
drop appreciably due to long standby periods, a bypass pipe of at
least 1" size with a balancing cock should be installed between
the boiler inlet and outlet. When the system first starts, the valve
should be slowly opened until the condensing ceases. This
adjustment remains at a permanent setting to establish required
temperature rise across the boiler.
The equipment shall be installed in accordance with those
installation regulations in force in the local area where the
installation is to be made. These shall be carefully followed in all
cases. Authorities having jurisdiction shall be consulted before
installations are made.

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LOCATION
When installing the boiler, consideration must be given to proper
location. Location selected should be as close to the stack or
chimney as practicable with adequate air supply and as centralized
with the piping system as possible. This location should also be
such that the gas ignition system components are protected from
water (dripping, spraying, etc.) during appliance operation and
service (circulator replacement, control replacement, etc.).
THE BOILER MUST NOT BE INSTALLED ON CARPETING.
THEBOILERSHOULD NOTBELOCATEDINANAREAWHEREIT
WILL BE SUBJECT TO FREEZING.
LOCATE IT NEAR A FLOOR DRAIN. THE BOILER SHOULD BE
LOCATEDINANAREAWHERE LEAKAGE FROMTHEBOILEROR
CONNECTIONS WILL NOT RESULT IN DAMAGE TO THE
ADJACENTAREA ORTOLOWERFLOORS OFTHESTRUCTURE.
WHEN SUCH LOCATIONS CANNOT BE AVOIDED, A SUITABLE
DRAINPAN SHOULD BE INSTALLED UNDER THEBOILER. Such
pans should be fabricated with sides at least 60mm (2-1/2") deep,
with length and width at least 50mm (2") greater than the diameter
of the boiler and must be piped to an adequate drain. The pan
must not restrict combustion air flow.
WARNING
KEEPINGBOILERAREACLEARANDFREEFROMCOMBUSTIBLE
MATERIALS, GASOLINEANDOTHERFLAMMABLEVAPORSAND
LIQUIDS.
WARNING
THEREISARISK IN USING FUELBURNING APPLIANCES SUCH
ASBOILERSIN ROOMS OR AREAS WHEREGASOLINE, OTHER
FLAMMABLE LIQUIDS OR ENGINE DRIVEN EQUIPMENT OR
VEHICLES ARE STORED, OPERATED OR REPAIRED.
FLAMMABLE VAPORS ARE HEAVY AND TRAVEL ALONG THE
FLOORANDMAYBEIGNITEDBYTHEIGNITERORMAINBURNER
FLAMESCAUSINGFIREOREXPLOSION. SOMELOCALCODES
PERMIT OPERATION OF GAS APPLIANCES IF INSTALLED
18 INCHES OR MOREABOVE THE FLOOR. THIS MAY REDUCE
THERISK IFLOCATION INSUCHANAREACANNOTBEAVOIDED.
WARNING
FLAMMABLE ITEMS, PRESSURIZED CONTAINERS OR ANY
OTHERPOTENTIAL FIRE HAZARDOUS ARTICLESMUSTNEVER
BE PLACED ON OR ADJACENT TO THE BOILER. OPEN
CONTAINERSOFFLAMMABLEMATERIALMUSTNOTBESTORED
ORUSED INTHESAME ROOM WITHTHE BOILER.
A hot water boiler installed above radiation level or as required by
the authority having jurisdiction, must be provided with a low water
cutoff device at the time of boiler installation.
AIRREQUIREMENTS
Provisions for combustion and ventilation air in accordance with
section 5.3, Air for Combustion and Ventilation, of the National
Fuel Gas Code, ANSI Z223.1, or sections 7.2, 7.3, or 7.4 of
CAN/CSA B149.1-00, Installation Codes, or applicable provisions
of the local building codes.
Provisions for vent, bleed and gas relief lines (when applicable).
Keep appliance area free of combustible or flammable liquids.
Do not obstruct the flow of combustion or ventilating air.
WARNING
FOR SAFE OPERATION PROVIDE ADEQUATE AIR FOR
COMBUSTION AND VENTILATION. AN INSUFFICIENT SUPPLY
OF AIR WILL CAUSE RECIRCULATION OF COMBUSTION
PRODUCTSRESULTING INAIR CONTAMINATIONTHATMAYBE
HAZARDOUS TO LIFE. SUCH A CONDITION OFTEN WILL
RESULT INA YELLOW, LUMINOUS BURNER FLAME, CAUSING
CARBONING OR SOOTING OF THE COMBUSTION CHAMBER,
BURNERS AND FLUE TUBES AND CREATES A RISK OF
ASPHYXIATION.
UNCONFINEDSPACE
In buildings of conventional frame, brick or stone construction,
unconfined spaces may provide adequate air for combustion, and
draft hood dilution.
If the unconfined space is within a building of tight construction
(buildingsusing the followingconstruction:weather stripping, heavy
insulation, caulking, vapor barrier, etc.) air for combustion,
ventilation, and draft hood dilution must be obtained from outdoors
or spaces freely communicating with the outdoors. The installation
instructions for confined spaces in tightly constructed buildings
must be followed to ensure adequate air supply.
CONFINEDSPACE
(a) U. S.INSTALLATIONS
When drawing combustion and dilution air from inside a
conventionally constructed building to a confined space, such a
space shall be provided with two permanent openings, ONE
WITHIN 12 INCHES OF THE ENCLOSURE TOP AND ONE
WITHIN 12 INCHES OF THE ENCLOSURE BOTTOM. Each
opening shall have a free area of at least one square inch per
1000 Btuh of the total input of all appliances in the enclosure, but
not less than 100 square inches.
If the confined space is within a building of tight construction, air
for combustion, ventilation, and draft hood dilution must be
obtained from outdoors. When directly communicating with the
outdoors or communicating with the outdoors through vertical
ducts, two permanent openings, located in the above manner,
shall be provided. Each opening shall have a free area of not less
than one square inch per 4000 Btuh of the total input of all
appliances in the enclosure. If horizontal ducts are used, each
opening shall have a free area of not less than one square inch
per 2000 Btuh of the total input of all appliances in the enclosure.
(b) CANADIANINSTALLATIONS
Ventilation of the space occupied by the boiler(s) shall be provided
by an opening for ventilation air at the highest practical point
communicating with outdoors. The total cross-sectional area shall
be at least 10% of the area of the combustion air opening but in no
case shall the cross-sectional area be less than 10 square inches
(6500 mm2)
In additional to the above, there shall be permanent air supply
opening(s) having a cross-sectional area of not less than 1 square
inch per 7,000 BTUH (310 mm2/KW) up to and including
1,000,000 BTUH plus 1 square inch per 14,000 BTU in excess of
1,000,000 BTUH. This opening(s) shall be located at, or ducted
to, a point neither more than 18" (450 mm) nor less than 6 inches
(150 mm) above the floor level.
Where power vented equipment is used in the same room as the
boiler, sufficient air openings must be supplied.
UNDERSIZED OPENINGS MAY RESULT IN INSUFFICIENT AIR
FORCOMBUSTION.

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Where an exhaust fan is installed in the same room with a boiler,
sufficient openings for air must be provided in the walls.
UNDERSIZEDOPENINGSWILLCAUSEAIRTOBEDRAWNINTO
THE ROOM THROUGH THE CHIMNEY, CAUSING POOR
COMBUSTION. SOOTING MAY RESULT WITH AN INCREASED
RISKOFASPHYXIATION.
CHEMICALVAPORCORROSION
WARNING
CORROSION OF THE FLUEWAYS AND VENT SYSTEM MAY
OCCUR IF AIR FOR COMBUSTION CONTAINS CERTAIN
CHEMICALVAPORSWHICHBREAKDOWNINTOACIDSATHIGH
TEMPERATURE. SUCHCORROSION MAYRESULTIN FAILURE
ANDRISK OFASPHYXIATION.
Water boiler corrosion and component failure can be caused by
the heating and breakdown of airborne chemical vapors. Spray
can propellants, cleaning solvents, refrigerator and air conditioning
refrigerants, swimming pool chemicals, calcium and sodium
chloride, waxes, and process chemicals are typical compounds
which are corrosive. These materials are corrosive at very low
concentration levels with little or no odor to reveal their presence.
Products of this sort must not be stored near the boiler. Also, air
which is brought in contact with the water boiler should not contain
any of these chemicals. If necessary, uncontaminated air should
be obtained from remote or outside sources.
INSTALLATIONCLEARANCES
These boilers are approved for installation on combustible flooring
in an alcove with minimum clearance to combustibles of:
TABLE4
HWB/HW HWB/HW HWB/HW HWB/HW HWB/HW
300 399 420 520 610 & 670
TOP 28"(711.2) 32" (812.8) 24"(609.6) 24"(609.6) 24" (609.6)
SIDES 6"(152.4) 6" (152.4) 24" (609.6) 24"(609.6) 24" (609.6)
REAR 6"(152.4) 6" (152.4) 24" (609.6) 24"(609.6) 24" (609.6)
VENT 6"(152.4) 6" (152.4) 6"(152.4) 6"(152.4) 6" (152.4)
Two inch (50.8mm) clearance is allowable from combustible
construction for hot water pipes.
Sufficient area should be provided at the front and rear of the unit
for proper servicing. Clearances of 24 inches (609.4mm) in the
rear and 48 inches (1,219mm) in the front are required by code. In
a utility room installation, the door shall be wide enough to allow
the boiler to enter or to permit the replacement of another appliance
such as a water heater.
LEVELLING
Each unit should be checked after installation to be certain that it is
level.
If the unit is not level, insert metal shims under the legs of the unit
to correct this condition.
SYSTEMCONNECTIONS
The system installation must conform to these instructions and to
the requirements of the local code authority having jurisdiction.
Good practice requires that all heavy piping be supported.
ATYPICALBOILERINSTALLATION
FIGURE1

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1.CONVENTIONALINSTALLATIONS
Allmodern hydronic type boilersareexceptionally fast heating units.
The low water volumes in relation to firing rates require special
attention to water flow rates for smooth, efficient operation. These
considerations for the A. O. Smith copper heat exchanger boilers
are covered below.
Conventional 100C (200F) drop in systems for a fully loaded boiler
will maintain the following approximate flow rates:
U.S. CANADIAN
MODELS MODELS LPM GPM
HW-300 HWB-300 87 23
HW-399 HWB-399 114 30
HW-420 HWB-420 132 35
HW-520 HWB-520 148 39
HW-670 HWB-610 175 46
Figure 1 shows a typical installation of the boiler with pipe sizing
and circulator selected by the installer to provide adequate water
flow whenever the boiler is firing.
In a system with several large zones of which any might be smaller
than approximately 1/3 of the system should include a hydronic
balancer as shown in fig. 1. The balancer connects between the
system supply and the return line before the circulator inlet.
Adjustment of the balancing cock should permit adequate boiler
flow rate when only the smallest zone is in operation.
Attention should be given to balancing inputs and water flow rates
where wide variations of system flow rates can occur.
The recommended minimum flow rates that will result in
approximately 300C (500F) temperature rise across the boiler are
as follows:
U.S. CANADIAN
MODELS MODELS LPM GPM
HW-300 HWB-300 34 9
HW-399 HWB-399 45 12
HW-420 HWB-420 53 14
HW-520 HWB-520 61 16
HW-610 HWB-610 69 18
HW-670 76 20
If system flow rate is unknown, or if zoning creates extreme
variations in flow rates, the boiler should be installed as shown
in fig. 2 for A. O. Smith LINEAR-TEMP installations.
2. LINEAR-TEMPINSTALLATIONS
A. New Installations
A.O. Smith LINEAR-TEMPsystems havebeendesigned to provide
efficient, trouble-free operation of the boiler sizes covered in this
manual with any of the following conditions:
a. Unknown system flow rate
b. Varying flow rate as with zoned systems
c. Multiple boiler installations
Figure 2 shows piping and accessory arrangement for a boiler
pumped independent of the primary system mains. Pipe sizing
and boiler loop pump selection data are shown in Table 5 for
several different temperature rises across the boilers.
ONEBOILERINSTALLED
INDEPENDENTOFTHEPRIMARYSYSTEM
FIGURE2
Total heating requirements for the building can be supplied by a
series of boiler loops all connecting to a common pipe joining the
system supply and return mains. The supply and return branches
of each boiler loop must join the common pipe only a short nipple
length apart. The different sets of branches should be installed
reasonably close together, but not necessarily to the short nipple
length as required for the supply and return of each set. These
branches may be made with tees or with welded connections.
The installer is reminded that the total boiler flow rates need not
match the system flow rate.
TABLE5
PUMPANDPIPE SIZINGDATA
(PIPINGFROMTEES INMAINTO BOILERBRANCHES)
Quantity and Model Temp. *Pump Pipe
U.S Canadian Rise°C (°F) G.P.M. Size Size
10(20) 23 1-1/2"PR 2"
HW-300 1HWB-300 15(30) 15 150 1-1/2"
15(30) 15 125 1-1/4"
20(40) 11 100 1"
10(20) 30 60-13 2"
HW-399 1HWB-399 15(30) 20 1-1/2"HV 1-1/2"
20(40) 15 150 1-1/2"
20(40) 15 125 1-1/4"
10(20) 32 60-13 2"
HW-420 1HWB-420 15(30) 21 1-1/2"HV 1-1/2"
20(40) 16 150 1-1/2"
20(40) 16 125 1-1/4"
10(20) 39 2-1/2" 2-1/2"
HW-520 1HWB-520 10(20) 26 1-1/2"HV 2"
17(35) 23 1-1/2"HV 1-1/2"
20(40) 20 150 1-1/2"
10(20) 51 60-13 3"
HW-670 1HWB-610 15(30) 34 2-1/2" 2-1/2"
17(35) 29 2" 2"
20(40) 25 1-1/2"HV 1-1/2"
NOTE: Pipe loop sizes and pump selections based on
50 equivalent feet of pipe and fittings.
*All pump sizes listed are B & G model numbers.

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NO. SUGGESTED ITEMS FOR INSTALLATION
1 Shortpipe nippleandpair ofboiler loop teesin piping
betweensystemsupply and return. One set per each
groupof boilers
2 Boilerpipeloop.See pipingsizing dataabove.
3 Boilercirculator.See pumpsizing data above.
4 Thermometer.
5 Theraltimeter.
6 Plugcock to control flow rate.
7 Safety flow switches. For interlock with other systems or
instead of low water cutoff.
8 Reliefvalve.
9 Withone -300, -399 or -420item9 is - sensing
elementofremotecontrol.
With a group of -300's, -399's or -420's, item 9 is - for
1st.boiler,thesensingelement asabove. Foradditional
boilers,install a 2nd.limit control if requiredby local codes.
Withany -520,-610or 670boilers,install 2nd.limitcontrol
hereif required by local code.
BOILERINLET-OUTLETSIZES
10 HWB-300- 1-1/4",HWB-399 -1-1/2", HWB-420-1-1/2",
HWB-520&HWB-610-2". CanadianModels
10 HW-300- 1-1/4",HW-399 -1-1/2", HW-420-1-1/2",
HW-520&HW-670-2". U.S. Models
MINIMUMBRANCHSIZESTOBOILERS
11 HWB-300-1-1/4" HWB-520,610(Singleboiler
HWB-399- 1-1/2" perpump) 2"
HWB-420- 1-1/2" CanadianModels
11 HW-300- 1-1/4" HW-520,670(Singleboiler
HW-399- 1-1/2" perpump) 2"
HW-420- 1-1/2" U.S. Models
12 Flow control valve. Required only if flow rate of system
primary is excessive for size of boiler branch tees or if
chilledwater main isabove boilers.
13 Systemsupplytemperature thermometer.
14 Boiler headers for three(3)boilers can be larger thanpipeloop,
ifdesired, toaidin balancing.
The system flow rate is selected to give the desired system
temperature drop - depending on the design criteria.
The boiler generator flow rates, on the other hand, should be
selected to give the temperature rise through the generator that is
both economical and offers the best generator efficiency.
The boiler temperature rise is normally between 100C and 200C
(200F and 400F). The system temperature that will be introduced
to the boiler (inlet temperature) plus the selected boiler temperature
riseselectedfromPUMPAND PIPE SIZING DATAshouldnotexceed
the high limit control setting of 1150C (2400F).
There should be a relation of the minimum system load to the size
boiler selected as the first firing or base boiler. This will stabilize
operation during minimum load periods.
B. Commercial Boiler Replacements
Application of LINEAR-TEMP®to a commercial boiler replacement
with an old multiple pump installation is an excellent way to
modernize the system. The A. O. Smith boiler(s) should be
installed on a pipe loop with a separate circulating pump selected
fromPUMPAND PIPE SIZINGDATATABLE.
Figure 3 shows a line drawing of how the system headers should
be connected to the pipe loop installed with the replacement
boiler(s). Make-up water connections and accessories are not
shown.
SCHEMATICOFTHE LINEAR-TEMP®SYSTEM
FIGURE3
Supply and return headers of the old system should be connected
to the boiler loop with a pair of tees set close together. The boiler
loop pump and the boiler(s) should be wired to operate only when
any of the system pumps are in operation. The number of zone
pumps that may be in operation at any particular time will take their
required flow rate out from the first tee in the boiler piping. This
waterwill be circulatedthrough theproper branches from thesupply
header to the zones calling for heat. The water will be brought
back to the return header and then into the second tee in the boiler
pipe loop. There will be no conflict between the boiler pump and
the zone pumps when the two tees in the boiler loop are placed
close together.
Normal use of flow control valves is required to prevent cross
circulation of zones as with any multiple pump system. Flow control
is not required on boiler circuit.
Attention should be given to balancing gas inputs and water flow
rates. Large systems with multiple boilers should include main
water temperature control (with or without outdoor reset) to stage
the boilers on and off in relation to the load on the system.
3. WATER SUPPLY LINE
These boilers can be used ONLY in a forced circulation hot water
heating system. Since most forced circulation systems will be of
the closed type, install the water supply line as shown on piping
diagrams, fig. 1 or 2.
Fast filling of large pipe, old radiator installations and pressure
purging of series loop systems (where high pressures are not
available) requires bypassing of the pressure reducing valve.
Generally, pressure purging is not possible with a well pump
system. High point air venting is essential.
If the system is of the open type, a pressure reducing valve will not
be required as the water supply to the system will be controlled by
a manually operated valve. An overhead surge tank is required.
4. EXPANSIONTANK
CAUTION
Aclosedsystem will exist ifa checkvalve (withoutbypass), pressure
reducing valve (without bypass), or a water meter (without bypass)
is installed in the cold water line between the water heater and
street main (or well).

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9
Excessive pressure may develop causing premature tank failure
or intermittent relief valve operation. This is not a warranty failure.
An expansion tank or a similar device may be required in the inlet
supply line between the appliance and the meter or valve to
compensate for the thermal expansion of water under supply
pressure, see figure 1.
An air separator as shown in the piping diagrams is recommended
especially for modern commercial hydronic systems.
5. VENTVALVES
It is recommended that automatic, loose key or screwdriver type
vent valves be installed at each convector or radiator.
6. MANIFOLDHEADERS
Split systems with individual supply and return lines from the boiler
room should normally have this piping connected to supply and
return manifold headers near the boiler. To achieve good water
distribution with maximum pressure drop for several circuits,
manifolds of at least 2-1/2" (64mm) diameter are suggested on
HWB/HW-399, HWB/HW-420, HWB/HW-520, HWB/HW-610 and
HW-670 units. HWB/HW-300 units should have 1-1/2" (38mm)
diameter manifolds.
The circuits should be spaced on the header at a minimum of
3" (76mm) center to center. Install a balancing cock in each return
line.
Manifold headers are recommended for split systems with or
without zone valves and also those installations with zone
circulators. If the system is to be split at remote points, good
practice requires special attention be given to main pipe sizing to
allow balancing of water flow.
The boiler piping system of a hot water boiler connected to heating
coils located in air handling units where they may be exposed to
refrigeratedair circulation mustbe equippedwith flow control valves
or other automatic means to prevent gravity circulation of the boiler
water during the cooling cycle.
7. COOLINGPIPING
When the boiler is used in conjunction with a refrigeration system
it must be installed so that the chilled medium is piped in parallel
with the boiler with appropriate valves to prevent the chilled medium
from entering the boiler, fig. 4.
Water temperature in the heating system must be reduced to less
than 1000F (38°C) before cooling system is started, or damage to
the chiller unit may occur.
SCHEMATICSHOWINGPROPER PIPINGISOLATION
OFTHEBOILERFROMTHECHILLER
FIGURE4
If the boiler is connected to chilled water piping or its heating coils
are exposed to refrigerated air, the boiler piping system must be
equipped with flow valves or other automatic means to prevent
gravity circulation through the boiler during the cooling cycle.
8. CIRCULATING PUMP
CONSTANT CIRCULATING PUMP OPERATION OF THE BOILER
VOIDS THE WARRANTY. Constant water flow through the unit will
“wash” away the copper’s natural protective coating. This is called
velocity erosion. This erosion is not as great a problem when
intermittent circulating operation is used per the recommended
installation procedure. Constant circulation of water through the
building’s system main is permissible as long as the water does
not constantly flow through the boiler. Only all bronze or stainless
steel circulators are to be used with the unit when it is installed in
HOTWATER SUPPLYSYSTEMS.
ATYPICALCIRCULATINGPUMP
FIGURE5
Although each circulator that requires oiling is oiled and operated
by the manufacturer, IT MUST BE OILED AGAIN BEFORE
OPERATED. Oil the three oil cups (2 on the motor, 1 on the pump)
as instructed on the oil tube supplied with the unit, fig 5.
Thereafter, during the heating season, lubricate the three oil cups
at least once every four months. Combination heating-cooling
systems should be lubricated every four months year ‘round.
Use 2 or 3 teaspoonsful in bearing oil cups, fig. 5, and 10 or
12 drops in the motor oil cups. Use No. 20 non-detergent motor
oil.
Follow the same oiling procedure if a replacement circulator is
installed into the system.
GASCONNECTIONS
WARNING
THIS BOILER IS NOT INTENDED TO OPERATEAT GAS SUPPLY
PRESSURE OTHER THAN SHOWN ON THE RATING PLATE.
EXPOSURE TO HIGHER GAS SUPPLY PRESSURE MAY CAUSE
DAMAGE TO GAS VALVES WHICH CAN RESULT IN FIRE OR
EXPLOSION. IF OVERPRESSURE HAS OCCURRED SUCH AS
THROUGHIMPROPERTESTINGOFGASLINESOREMERGENCY
MALFUNCTIONOFTHESUPPLYSYSTEM,THEGASVALVESMUST
BE CHECKED FOR SAFE OPERATION. MAKE SURE THAT THE
OUTSIDE VENTS ON THE SUPPLY REGULATORS AND THE
SAFETYVENTVALVESARE PROTECTEDAGAINSTBLOCKAGE.
THESE ARE PARTS OF THE GAS SUPPLY SYSTEM, NOT THE
BOILER. VENTBLOCKAGE MAYOCCURDURINGICEBUILD-UP
ORSNOWSTORMS.
WHEN LOCAL CODES REQUIRE A MAIN MANUAL SHUTOFF
VALVEOUTSIDETHEBOILERJACKET,ASUITABLEMAINMANUAL
SHUTOFF VALVE MUST BE INSTALLED IN A LOCATION
COMPLYINGWITH THOSE CODES.

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2A.SIZING GAS SUPPLY LINE (For single boiler installations and
forinstallations of multiplesof twoorthree of samesizeboilers).
Use table 6, or CAN/CSA B149.1-00 (latest recent edition) to size
iron pipe or equivalent gas supply line. Table 6 is based on a
pressure drop of 0.3 inches of water and a specific gravity of 0.60
approximately that of natural gas. (LP gas has an S.G. of about
1.53). If the service pressure is five inches water column or less,
useone pipe size largerthanspecified in table 6inorder to minimize
pressure drop in the line.
TABLE6
MAXIMUMCAPACITYOFPIPEINCUBIC FEETOFGAS PER
HOUR(BASED UPONAPRESSURE DROPOF0.3 INCHWATER
COLUMNAND0.6SPECIFICGRAVITY GAS)
Length
Meters
From Gas (Nominal Iron Pipe Size (Inches)
Meter 1/2 3/4 1 1 1/4 1 1/2 2 2 1/2 3 4
3 (10) 132 278 520 1,050 1,600 3,050 4,800 8,500 17,500
6 (20) 92 190 350 730 1,100 2,100 3,300 5,900 12,000
9 (30) 73 152 285 590 890 1,650 2,700 4,700 9,700
12 (40) 63 130 245 500 760 1,450 2,300 4,100 8,300
15 (50) 56 115 215 440 670 1,270 2,000 3,600 7,400
18 ((60) 50 105 195 400 610 1,150 1,850 3,250 6,800
21 (70) 46 96 180 370 560 1,050 1,700 3,000 6,200
24 (80) 43 90 170 350 530 990 1,600 2,800 5,800
27 (90) 40 84 160 320 490 930 1,500 2,600 5,400
30 (100) 38 79 150 305 460 870 1,400 2,500 5,100
38 (125) 34 72 130 275 410 780 1,250 2,200 4,500
45 (150) 31 64 120 250 380 710 1,130 2,000 4,100
53 (175) 28 59 110 225 350 650 1,050 1,850 3,800
60 (200) 26 55 100 210 320 610 980 1,700 3,500
*The heating value of Natural Gas is approximately 1,050 Btu/Ft.3.
Propane (LP) Gas has a heating value of approximately 2,500 Btu/Ft3.
1 cu. meter=35.31 cu. feet.
Where it is necessary to use more than the average number of
pipe fittings i.e. elbows, tees, and valves in gas supply line, use a
pipe larger than specified to compensate for increased pressure
drop.
2B. SIZING GAS SUPPLY LINE (For multiples of over three boilers
of same size or for multiple installations of two or more mixed
sizes).
Capacities in cubic feet per hour of 0.60 specific gravity gas for
different sizes and lengths are shown in table 6. No additional
allowance is necessary for an ordinary number of fittings.
Applications of the gravity factor converts the figures given in table
6 to capacities with another gas of different specific gravity. Such
application is accomplished by multiplying the capacities given in
table 6 by the multipliers shown in table 7.
To determine the size of each section of gas piping in a system
within the range of table 6 proceed as follows:
•Determine the gas demand of each appliance to be attached
to the piping system. When table 6 is to be used to select the
piping size, calculate the gas demand in terms of cubic feet per
hour for each piping system outlet. The gas demand for an
appliance can be found by dividing its heat input rate by the
gas’s heating value.
• Obtain or determine the length of piping from the gas meter or
service regulator to the appliance(s).
ITISIMPORTANTTOGUARDAGAINSTGASVALVEFOULINGFROM
CONTAMINANTSINTHEGASWAYS. SUCHFOULINGMAYCAUSE
IMPROPEROPERATION, FIRE OR EXPLOSION.
IF COPPER SUPPLY LINES ARE USED THEY MUST BE
CERTIFIEDFORGAS SERVICE.
BEFORE ATTACHING THE GAS LINE BE SURE THAT ALL GAS
PIPE IS CLEAN ON THE INSIDE.
TOTRAPANYDIRTORFOREIGNMATERIALINTHE GASSUPPLY
LINE, A DIRT LEG (SOMETIMES CALLED DRIP LEG or sediment
trap) MUST BE INCORPORATED IN THE PIPING, SEE FIG. 1. The
dirt leg must be readily accessible and not subject to freezing
conditions. INSTALL IN ACCORDANCE WITH
RECOMMENDATIONS OF SERVING GAS SUPPLIERS. (Refer to
National Fuel Gas Code, ANSI Z223.1 and/or
CAN/CSA-B 149.1-00 Installation Codes.
To prevent damage, care must be taken not to apply too much
torque when attaching gas supply pipe to gas valve gas inlet.
Fittings and unions in the gas line must be metal to metal type.
Apply joint compounds (pipe dope) sparingly and only to the male
threads of pipe joints. Do not apply compound to the first two
threads. Use compounds resistant to the action of liquefied
petroleum gases.
THE BOILER AND ITS GAS CONNECTIONS MUST BE LEAK
TESTED BEFORE PLACING THE BOILER IN OPERATION. Use
soap and water solution or other material acceptable for the
purposeinlocatinggasleaks. DONOTUSE MATCHES,CANDLES,
FLAMEOROTHERSOURCESOFIGNITIONFORTHISPURPOSE.
DISCONNECT THE BOILER AND ITS MAIN MANUAL GAS
SHUTOFF VALVE FROM THE GAS SUPPLY PIPING SYSTEM
DURING ANY PRESSURE TESTING OF THE GAS SUPPLY
SYSTEMOVER 1/2 PSIG(3.5kPa).. THEGASSUPPLYLINEMUST
BE CAPPED WHEN NOT CONNECTED TO THE BOILER.
THE BOILER MUST BE ISOLATED FROM THE GAS SUPPLY
PIPINGSYSTEM BY CLOSING ITSMAINMANUALGASSHUTOFF
VALVEDURINGANYPRESSURETESTING OFTHEGASSUPPLY
PIPING SYSTEM AT TEST PRESSURES EQUAL TO OR LESS
THAN 1/2 PSIG (3.5kPa).
PURGING
Gas line purging is required with new piping or systems in which
air has entered.
CAUTION
PURGING SHOULD BE PERFORMED BY PERSONS
EXPERIENCEDIN THISTYPEGAS SERVICETOAVOID RISKOF
FIREOR EXPLOSION. PURGE DISCHARGEMUSTNOT ENTER
CONFINEDAREASOR SPACESWHEREIGNITIONCANOCCUR.
THEAREAMUSTBEWELLVENTILATEDANDALLSOURCES OF
IGNITIONMUSTBEINACTIVATEDORREMOVED.
1. CORRECTGAS
Make sure the gas on which the boiler will operate is the same as
that specified on the boiler rating plate. Do not install the boiler if
equipped for a different type gas — consult your supplier.

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• In table 6, select the row showing the distance to the most
remote outlet or the next longer distance if the table does not
give the exact length. This is the only distance used in
determining the size of any section of gas piping. If the gravity
factor is to be applied, the values in the selected row of table 6
are multiplied by the appropriate multiplier from table 7.
• Total the gas demands of all appliances on the piping system.
Enter table 6, on the left hand side, at the row equal to or just
exceeding the distance to the most remote outlet. Select the
pipe size in the row with a capacity equal to or just exceeding
the total gas demand. This is the required main gas supply
line size leading away from the gas meter or regulator. To
determine the pipe size required for each branch outlet leading
away from the main supply line, determine the gas demand for
that outlet. Enter table 6 on the same row, and select the branch
pipe size for a capacity equal to or just exceeding the demand
at that outlet. The main line can be resized for a lesser capacity
after each branch outlet, since the gas demand is reduced.
Total the gas demands of all remaining appliances branching
off downstream on the main gas line. Re-enter table 6 in the
same row and select the appropriate pipe size with adequate
capacity. Repeat the branch sizing and main line re-sizing for
any remaining appliances in the system.
EXAMPLE
Job Condition:
Determining the required gas pipe size for a system composed of
two HWB/HW-420 boilers and two HWB/HW-610 boilers to be
installed as a multiple group, 50 lineal feet from meter. Gas to be
used has a .60 specific gravity and heating value of 1,000 Btu per
cubic foot.
Solution:
2 HWB/HW-420 Boilers = 840,000 Btuh
2 HWB/HW-610 Boilers = 1,220,000 Btuh
Total Btuh Input = 2,060,000 Btuh
Total Btuh Input = 2,060,000 Btuh = 2,060 cf/h
Btu per Cubic Foot of Gas 1,000
With a cubic foot per hour demand of 2,060 and with 50 lineal feet
of gas supply line, table 6 shows a pipe size of 3" (76mm) is
required.
NOTE: For other than .60 specific gravity, apply multiplier factor
as shown in table 7.
TABLE7
MULTIPLIERS TOBE USEDWITH TABLE6 WHENAPPLYING
THEGRAVITYFACTORTOOTHERTHAN.60SPECIFICGRAVITY
Specific Specific
Gravity Multiplier Gravity Multiplier
.35 1.31 1.00 .78
.40 1.23 1.10 .74
.45 1.16 1.20 .71
.50 1.10 1.30 .68
.55 1.04 1.40 .66
*.60(Nat.) 1.00 *1.50(Prop.) .63
.65 .96 1.60 .61
.70 .93 1.70 .59
.75 .90 1.80 .58
.80 .87 1.90 .56
.85 .84 *2.00 (Butane) .55
.90 .82 2.10 .54
*Use these correction factors if exact specific gravity of the gas is not
known.
GAS PRESSUREREGULATORS
The gas pressure regulator is included in the combination gas
valve, fig. 6, and is set to operate on the gas specified on the boiler
model and rating plate.
Periodically check main burner, fig. 41, and pilot flame, fig. 42, for
proper operation. This should be checked every six months.
Do not subject the gas valve to inlet gas pressures of more than
14" W.C. (1/2 P.S.I.). If higher gas pressures are encountered, a
service regulator is necessary.
TABLE8
CORRECTMANIFOLDPRESSUREFORFULL
BOILERINPUT(IN INCHESOFWATERCOLUMN)
Model Rated Manifold Pressure
Number Input Natural Propane
HWB/HW-300 300,000 3.5 10.0
HWB/HW-399 399,000 3.2 9.5
HWB/HW-420 420,000 3.5 10.0
HWB/HW-520 520,000 3.5 10.0
HWB/HW-610 610,000 3.5 10.0
HW-670 Nat. 660,000 3.5
HW-670 Prop. 670,000 10.0
Adjustment, if required, is performed as follows:
1. Set primary system temperature control dial (thermostat) at
lowest setting so that boiler will not call for heat.
2. Attach a pressure gauge to the tapping in the control string
elbow.
3. Reset primary system temperature control dial (thermostat)
to highest setting. Main burner will now ignite.
4. With main burnerfiring, adjustpressure, ifnecessary,byturning
pressure regulator adjusting screw with a screwdriver.
• Clockwise to increase pressure.
• Counterclockwise to decrease pressure.
5. Set primary system temperature control dial (thermostat) to
lowest setting.
6. Remove pressure gauge and replace sealing plug.

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7. Set primary system temperature control dial (thermostat) to
desired setting.
WARNING
DO NOT INCREASE GAS PRESSUREABOVE THAT SPECIFIED
ON THE RATING PLATE, AS OVERFIRING WILL RESULT IN
DAMAGE TO THE BOILER, AS WELL AS INCREASED RISK OF
FIRE,SOOTINGANDASPHYXIATION.
If gas pressure regulator cannot be adjusted to correct pressure
with sufficient gas pressure at the valve, replace with new gas
valve.
VENTINGTHE BOILER- STANDARD VENTING
WARNING
THE INSTRUCTIONS IN THIS SECTION ON VENTING THE
BOILERMUSTBEFOLLOWEDTOAVOID CHOKEDCOMBUSTION
OR RECIRCULATION OF FLUE GASES. SUCH CONDITIONS
CAUSESOOTINGOR RISKS OF FIREANDASPHYXIATION.
TYPE B VENTING MAY BE USED WITH THESE BOILERS. ALL
LOCAL UTILITY REGULATIONS ON VENTING SHOULD BE
FOLLOWED.
ROBERTSHAW®7000DERHC
HWB/HW-300, 399,-420, -520, -610, -670 NATURAL GAS WITH I.I.D.
HW-300, -399, -420, -520, -670 LP GAS WITH I.I.D. U.S. ONLY
ROBERTSHAW®7000ERHC (LP)
HWB/HW-300, 399,-420, -520, -610 SINGLE STAGE
STANDING PILOT, CANADIAN ONLY
FIGURE6
For boilers for connection to gas vents or chimneys, vent sizing,
installation and termination shall be in accordance with Part 7,
Venting ofEquipment, of theNational Fuel GasCode,ANSI Z223.1,
or Section 7, Venting Systems andAir Supply forAppliances, of the
CAN/CSA B149.1-00, Installation Codes, or applicable provisions
of the local building codes.
Vent connectors serving appliances vented by natural draft shall
not be connected into any portion of mechanical draft systems
operating under positive pressure.
The minimum distance from adjacent public walkways, adjacent
buildings, openable windows and building openings shall not be
less than those values specified in the National Fuel Gas Code,
ANSI Z223.1 and/or CAN/CSA B149.1-00, Installation Codes;
Stack or chimney must be a minimum height of 12" (305mm)
above the annual snow fall to prevent blockage.
Building materials must not come in contact with combustion
products from stack or chimney, due to the degradating properties
of flue products.
Flue products must have a minimum clearance of 4 feet (1.22m)
horizontally from, and in no case above or below, unless a 4-foot
(1.22m) horizontal distance is maintained, from electric meters,
gas meters, regulators and relief equipment.
The Canadian B149.1-00, Installation Code specifies a 6 foot
horizontal vent terminal clearance to gas and electric meters and
relief devices (this clearance is specified as 4 feet in the U.S.
under the National Fuel Gas Code, ANSI/Z223.1). Therefore
instruction provision 134.1-b19(d), which specifies compliance
with the 4 foot clearance, as applies in the U.S. only, and the
B149.1-00 Installation Code applies in Canada.
1. DRAFTHOOD
The draft hood furnished with this boiler must be installed without
alteration. Provision must be made if the boiler is installed in
confined space or a small boiler room to accommodate draft hood
spillage and avoid risks described above. The upper air opening
called for in the AIR REQUIREMENTS section of this manual is for
this purpose.
2. VENTCONNECTION
Size and install proper size vent pipe. Do not reduce pipe size to
less than that of the draft hood outlet.
Horizontal runs of vent pipe shall be securely supported by
adequately placed (approximately every 4 feet or 1 meter),
noncombustible hangers and/or slip joints suitable for the weight
and design of the materials employed to prevent sagging and to
maintain a minimum upward slope of 1/4" (21mm/m) per foot
from the boiler to the vent terminals, fig. 7. Dampers or other
obstructions must not be installed in the vent. Be sure that the vent
pipe does not extend beyond the inside wall of the chimney.
VENTPIPEINSTALLATION
FIGURE7
® Robertshaw is a registered trademark of Fulton Controls Corp.

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After it has been determined that each appliance remaining
connected to the common venting system properly vents when
tested as outlined above, return doors, windows, exhaust fans,
fireplace dampers and any other gas burning appliance to their
previous conditions of use.
Any improper operation of the common venting system should be
corrected so the installation conforms with the latest edition of
CAN/CGA B149.1-00 (latest edition). When resizing any portion of
the common venting system, the common venting system should
be resized to approach the minimum size as determined using
the appropriate tables in Appendix G in CAN/CSA B149.1-00.
4.MULTIPLE VENTTABLE
Table 9 has been compiled to show the material sizes in a Type B
doublewall combined vent system. Refer to
CAN/CSA B149 .1-00 (latest edition), or the ASHRAE 1983
Equipment Volume for further information.
A combined vent system is one in which two or more boilers at one
level are attached to a common vent.
In order to use table 9, the connector rise and total vent height
must be known. Connector rise is vertical distance from the draft
hood outlet to the point where the manifold connection is made.
Total vent height is the least vertical distance from a draft hood
outlet to the top of the vent. Local codes or utility requirements
often govern termination height. ULC listed doublewall gas vents,
up through 24" (610mm) diameter, can be installed in heated and
unheated areas and can pass through floors, ceilings, partitions,
walls and roofs, provided the required one inch clearance is
observed. These vents should be installed in accordance with
CAN/CSA B149.1-00 (latest edition).
EXAMPLESHOWINGUSEOFTHEHWB/HW-610 COMBINEDVENT
SIZINGTABLE9
FIGURE8
Where a continuous or intermittent back draft is found to exist the
cause must be determined and corrected. A special vent cap may
be required. If the back draft cannot be corrected by the normal
methods or if a suitable draft cannot be obtained, a blower type
flue gas exhauster may be employed to ensure proper venting and
correct combustion if permitted by local codes.
WARNING
FAILURE TO CORRECT BACK DRAFTS WILL CAUSE AIR
CONTAMINATIONANDUNSAFECONDITIONS.
Vent connectors serving appliances vented by natural draft shall
not be connected into any portion of mechanical draft systems
operating under positive pressure.
3.CONNECTING BOILER TO ACOMMON VENT
Do not connect the boiler to a common vent or chimney with solid
fuel burning equipment. This practice is prohibited by many local
building codes as is the practice of venting gas fired equipment to
the duct work of ventilation systems.
Where a separate vent connection is not available and the vent
pipe from the boiler must be connected to a common vent with oil
burning equipment, the vent pipe should enter the common vent
or chimney at a point ABOVE the flue pipe from the oil fired unit.
Where two or more appliances vent into a common vent connector
or manifold, the area of the common vent or vent connector should
at least equal the area of the largest vent connector plus 50% of
the areas of the additional draft hood outlets.
When removing a boiler from a system with a common vent, use
the following steps:
Be sure the other appliances connected to the common vent are
not in operation.
Seal any unused openings in the common venting system.
Visually inspect the venting system for proper size and horizontal
pitch and determine there is no blockage or restriction, leakage,
corrosion and other deficiencies which could cause an unsafe
condition.
WARNING
Ensuresufficient supply andventilation air. Undernocircumstances
should the equipment room where the boiler is installed ever be
under negative pressure. Insufficient air supply can interfere with
combustion and ventilation of this boiler resulting in unsafe
conditions.
Insofar as is practical, close all building doors and windows and
all doors between the space in which the appliances remaining
connected to the common venting system are located and other
spaces of the building. Turn on clothes dryers and any appliance
not connected to the common venting system. Turn on any exhaust
fans, such as range hoods and bathroom exhausts, so they will
operate at maximum speed. Close fireplace dampers.
Place in operation the appliance being inspected. Follow the
lighting instructions. Adjust thermostat so appliance will operate
continuously.
Test for spillage at the draft hood relief opening after five minutes
of main burner operation. Use the flame of a match or candle.

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MODELHW/HWB-610 BOILER
Input: 610,000 Btuh Draft Hood Outlet 12"
Required Connector or Smoke Pipe Diameter
Connector Total Vent Height(Measured in Feet Above Draft Hood)
Rise in 10 15 20 30 40 50 60 80 100
Feet Connector Diameter (in Inches)
1 161414141414141414
2 141414141412121212
3 141412121212121212
4 or more 12 12 12 12 12 12 12 12 12
Number Total Total Vent Height(Measured in Feet Above Draft Hood)
if Units Input 10 15 20 30 40 50 60 80 100
Combined Btuh x 1000 Manifold and Common Vent Diameter (in Inches)*
2 1220 18 18 16 16 14 14 14 14 14
3 1830 22 20 20 18 18 16 16 16 14
4 2440 26 24 22 20 20 18 18 18 16
5 3050 28 26 26 24 22 22 20 20 18
6 3660 32 28 28 26 24 24 22 22 20
7 4270 34 32 30 28 26 24 24 22 22
8 4880 36 34 32 30 28 26 26 24 24
9 5490 38 36 34 30 30 28 28 26 24
10 6100 40 38 36 32 30 30 28 26 26
11 6710 42 38 38 34 32 30 28 28 26
12 7320 44 42 38 36 34 32 32 30 28
MODELHW/HWB-300 BOILER
Input: 300,000 Btuh Draft Hood Outlet 8"
Required Connector or Smoke Pipe Diameter
Connector Total Vent Height(Measured in Feet Above Draft Hood)
Rise in 10 15 20 30 40 50 60 80 100
Feet Connector Diameter (in Inches)
1 101010101010101010
2 101010101010101010
3 101010101010101010
4 or more
Number Total Total Vent Height(Measured in Feet Above Draft Hood)
if Units Input 10 15 20 30 40 50 60 80 100
Combined Btuh x 1000 Manifold and Common Vent Diameter (in Inches)*
2 600 14 12 12 12 10 10 10 10 10
3 900 16 14 14 14 12 12 12 12 12
4 1200 18 16 16 14 14 14 14 12 12
MODELHW/HWB-399 BOILER
Input: 399,000 Btuh Draft Hood Outlet 10"
Required Connector or Smoke Pipe Diameter
Connector Total Vent Height(Measured in Feet Above Draft Hood)
Rise in 10 15 20 30 40 50 60 80 100
Feet Connector Diameter (in Inches)
1 121212121212121212
2 121212101010101010
3 121010101010101010
4 or more 10 10 10 10 10 10 10 10 10
Number Total Total Vent Height(Measured in Feet Above Draft Hood)
if Units Input 10 15 20 30 40 50 60 80 100
Combined Btuh x 1000 Manifold and Common Vent Diameter (in Inches)*
2 798 14 14 14 12 12 12 12 12 12
3 1197 18 16 16 14 14 14 14 14 12
4 1596 20 20 18 16 16 16 14 14 14
MODELHW/HWB-420 BOILER
Input: 420,000 Btuh Draft Hood Outlet 10"
Required Connector or Smoke Pipe Diameter
Connector Total Vent Height(Measured in Feet Above Draft Hood)
Rise in 10 15 20 30 40 50 60 80 100
Feet Connector Diameter (in Inches)
1 121212121212121212
2 121212101010101010
3 121010101010101010
4 or more 10 10 10 10 10 10 10 10 10
Number Total Total Vent Height(Measured in Feet Above Draft Hood)
if Units Input 10 15 20 30 40 50 60 80 100
Combined Btuh x 1000 Manifold and Common Vent Diameter (in Inches)*
2 840 14 14 14 12 12 12 12 12 12
3 1260 18 16 16 14 14 14 14 14 12
4 1680 20 20 18 16 16 16 14 14 14
MODELHW/HWB-520 BOILER
Input: 520,000 Btuh Draft Hood Outlet 10"
Required Connector or Smoke Pipe Diameter
Connector Total Vent Height(Measured in Feet Above Draft Hood)
Rise in 10 15 20 30 40 50 60 80 100
Feet Connector Diameter (in Inches)
1 141414121212121212
2 121212121212121212
3 121212121010101010
4 or more 12 12 12 12 10 10 10 10 10
Number Total Total Vent Height(Measured in Feet Above Draft Hood)
if Units Input 10 15 20 30 40 50 60 80 100
Combined Btuh x 1000 Manifold and Common Vent Diameter (in Inches)*
2 1040 16 16 14 14 14 14 12 12 12
3 1560 20 18 18 16 16 14 14 14 14
4 2080 22 22 20 18 18 18 16 16 14
5 2600 26 24 22 20 20 18 18 18 18
6 3120 28 26 24 22 22 20 20 18 18
7 3640 30 28 26 24 24 22 22 20 20
8 4160 32 30 28 26 24 24 22 22 20
TABLE9,COMBINED VENTSIZINGTABLES
Known: (5) model HWB/HW-610 boilers. (See illustration).
Connector rise - 2' (Note 1' is minimum). Total vent height
30'.
Problem: Determine diameter of connector, manifold and
common vent.
Procedure: EnterthetopoftheHWB/HW-610table(totalventheight)
at30' andthesideat 2'(connectorrise). A14" connector
diameter is indicated for each connector rise.
To determine the manifold and common vent size, enter this table
(total vent height) at 30 and the side at 5 boilers. A manifold
diameter of 24" (610mm) is indicated.
MODELHW/HWB-670 BOILER
Input: 660,000 or 670,000 Btuh Draft Hood Outlet 12"
Required Connector or Smoke Pipe Diameter
Connector Total Vent Height(Measured in Feet Above Draft Hood)
Rise in 10 15 20 30 40 50 60 80 100
Feet Connector Diameter (in Inches)
1 161414141414141414
2 141414141412121212
3 141412121212121212
4 or more 12 12 12 12 12 12 12 12 12
Number Total Total Vent Height(Measured in Feet Above Draft Hood)
if Units Input 10 15 20 30 40 50 60 80 100
Combined Btuh x 1000 Manifold and Common Vent Diameter (in Inches)*
2 1340 18 18 16 16 14 14 14 14 14
3 2010 22 20 20 18 18 16 16 16 14
4 2680 26 24 22 20 20 18 18 18 16
5 3350 28 26 26 24 22 22 20 20 18
6 4020 32 28 28 26 24 24 22 22 20
7 4690 34 32 30 28 26 24 24 22 22
8 5360 36 34 32 30 28 26 26 24 24
9 6030 38 36 34 30 30 28 28 26 24
10 6700 40 38 36 32 30 30 28 26 26
11 7370 42 38 38 34 32 30 28 28 26
12 8040 46 44 40 38 36 34 34 32 30

1515
1515
15
VENTINGMAINTENANCE - STANDARD VENTING
It is recommended that the heating surfaces and vent piping of
the appliance be checked every six months for dust, deterioration
and carbon deposits. Remove all soot or other obstructions from
chimney and flue which will retard free draft. Replace any
damaged or deteriorated parts of the venting system.
Qualified servicers should follow this procedure when the boiler’s
external heating surfaces and vent pipe need cleaning.
CAUTION
DO NOT USEANYLON BRUSH OR OTHER STATIC CREATING
MATERIAL TO CLEAN DUST AND CARBON DEPOSITS FROM
HEATINGSURFACESANDVENT.
SUCH DEPOSITS ARE FLAMMABLE AND MAY BE IGNITED BY
STATIC ELECTRICITY. USEAMETALBRUSHTOMINIMIZE THE
DANGEROFEXPLOSION.
1. Turn off the electrical power (main manual gas shutoff and
pilot valves, if applicable).
Allow boiler parts and vent to cool before disassembly.
2. Remove the boiler draft diverter and vent pipe running to the
chimney.
• Check parts and chimney for obstructions and clean as
necessary.
3. Remove burner from boiler and other metal parts as required
to clean and vacuum the heat exchanger and combustion
coils.
• Refer to parts list supplied with this manual for
disassembly aid.
4. Reinstall the parts removed in steps 2 and 3.
• Be sure the vent pipe has a minimum upward pitch of one
quarter inch per foot of length (21mm/m) and is sealed as
necessary.
5. Restore electrical power and gas supply to boiler.
• Place boiler in operation by following the lighting
instructions in this manual.
• Check for gas leaks and proper boiler and vent operation.
VENTING- SIDEWALL
(OPTIONAL)POWER VENTSYSTEM
If you are installing the optional Power Vent Kit, refer to your
HWB/HW Power Vent Kit Installation Instructions for proper wiring
and installation procedures. Contact your local A.O. Smith
representative for details.
VENTINGSYSTEM
HAVEVENTING SYSTEM CHECKEDEVERYSIX MONTHS FOR
OBSTRUCTIONSAND/ORDETERIORATION INVENT PIPING.
A. Insofar as is practical, close all doors, windows and air inlets
to the building. Turn on all exhaust fans (range hood,
bathroom exhaust, etc.) so they will operate at their maximum
speed. Close fireplace dampers.
B. After allowing appliance to operate for five minutes, test for
spillage at the draft hood relief opening.
C. “CHECKING THE DRAFT. Operate vent connected gas
utilization equipment for several minutes and check to see
that the combustion products are going up the chimney or
gas vent properly by passing a lighted match or taper around
the edge of the relief opening of the draft hood. If the chimney or
gas vent is drawing properly, the match flame will be drawn into
the draft hood. If not, the combustion products will tend to
extinguish this flame. IF THE COMBUSTION PRODUCTS ARE
ESCAPING FROM THE RELIEF OPENING OF THE DRAFT
HOOD,DO NOT OPERATETHEEQUIPMENT UNTILPROPER
ADJUSTMENT OR REPAIRS ARE MADE TO PROVIDE
ADEQUATE DRAFTTHROUGHTHECHIMNEYORGASVENT.”
D. Next, turn on all other fuel burning appliances within the same
room so they will operate at their full input.
Repeat step C above, checking the draft on each appliance.
FIGURE9
SAFETYRELIEF VALVES
Your local code authority may have other specific relief valve
requirements not covered below.
WARNING
THE PURPOSE OF A SAFETY RELIEF VALVE IS TO AVOID
EXCESSIVE PRESSURE OR TEMPERATURE INTO THE STEAM
RANGE WHICH MAY CAUSE SCALDING AT FIXTURES, TANK
EXPLOSION,SYSTEM OR BOILER DAMAGE.
TOAVOID SCALDING OR WATER DAMAGEADRAIN LINE MUST
BE CONNECTED TO A RELIEF VALVE TO DIRECT DISCHARGE
TOASAFE LOCATION. ADRAIN LINE MUST NOT BE REDUCED
FROM THE SIZE OF THE VALVE OUTLET AND IT MUST NOT
CONTAINANYVALVES BETWEENTHE BOILERANDTHE RELIEF
VALVEORTHERELIEFVALVEANDTHEDRAINEXIT. INADDITION,
THERE SHOULD NOT BE ANY RESTRICTIONS IN A DRAIN LINE
NOR SHOULD IT BE ROUTED THROUGH AREAS WHERE
FREEZING CONDITIONS MIGHT OCCUR. DO NOT THREAD OR
CAPTHEDRAINLINEEXIT. RESTRICTINGOR BLOCKINGADRAIN
LINE WILL DEFEAT THE PURPOSE OF THE RELIEF VALVE AND
MAY CREATE AN UNSAFE CONDITION. INSTALLA DRAIN LINE
WITHADOWNWARDSLOPESUCHTHATITNATURALLYDRAINS
ITSELF.
If any safety relief valve is replaced, the replacement valve must
comply with the latest version of the ASME Boiler and Pressure
Vessel Code, Section IV or CSA B51, as applicable. Select a relief
valvewith a dischargeNOT lessthan the boiler input,and a pressure
rating NOT exceeding the working pressure of any component in
the system.
A. O. Smith supplies Canadian HW boilers for hot water supply
systems with a 125 psi pressure relief valve. This valve must be
installed in the water outlet as near to the boiler as possible.
A. O. Smith United States HW and Canadian HWB boilers for space
heating are shipped with a 50 psi pressure relief valve. This valve
must be installed in the water outlet as near to the boiler as possible.
An ASME rated temperature and pressure relief valve must be
installed on each and every water storage tank in a hot water supply
system.

1616
1616
16
The storage tank temperature and pressure (T & P) relief valve
must comply with the applicable construction provisions of the
Standard for Relief Valves and Automatic Gas Shutoff Devices for
Hot Water Supply Systems, Z21.22 and/or CAN1-4.4. The T & P
valve must be of the automatic reset type and not embody a
single-use type fusible plug, cartridge or linkage.
The T & P relief valve should have a maximum temperature rating
of 1000C (2100F), a pressure rating NOT exceeding the lowest
rated working pressure of any system component, and a discharge
capacity exceeding the total input of the water boilers supplying
water to the storage tank.
Locate the T & P relief valve (a) in the top of the storage tank, or (b)
in the side of the tank on centerline within the upper 6 inches from
the top of the tank. See figures 20 to 31. Tapping shall be threaded
in accordance with the latest version of the Standard for Pipe
Threads, General Purpose (inch), ANSI/ASME B1.20.1
Mark location with a Class lll label.
See ANSI Z21.10.1, Part 1, MARKING, See CAN/CSA B149.1-00.
WIRINGCONNECTIONS
CAUTION
LABEL ALL WIRES PRIOR TO DISCONNECTION WHEN
SERVICING CONTROLS. WIRING ERRORS CAN CAUSE
IMPROPERANDDANGEROUS OPERATION.
VERIFYPROPER OPERATIONAFTER SERVICING.
1. CONVENTIONALINSTALLATIONS
ALLELECTRICALWORKMUSTBE INSTALLEDINACCORDANCE
WITHNATIONALELECTRICALCODE,ANSI/NFPA70AND/ORTHE
CANADIANELECTRICALCODE,PART1,CSAC22.1,ELECTRICAL
CODEAND MUST CONFORMTO LOCALREGULATIONS.
The boiler, when installed, must be electrically bonded to ground
in accordance with the requirements of the authority having
jurisdiction or, in the absence of such requirements, with the
National Electrical Code, ANSI/NFPA 70 and/or the Canadian
Electrical Code Part 1, CSA C22.1, Electrical Code.
STRICT ADHERENCE TO PIPING AND WIRING DIAGRAMS IS
REQUIREDTOPREVENTCONSTANTPUMPOPERATIONWHEN
SYSTEMTEMPERATURE CONTROLISSATISFIED. OTHERWISE
THE WARRANTY IS VOID AS STIPULATED IN THE LIMITED
WARRANTYONTHEINSTRUCTIONS MANUAL.
The electrical connections must be made so that the circulator will
operate before the gas valve opens. At no time may the controlling
system allow the burner to fire when there is no water flow through
the boilers.
Refer to the diagrams in fig’s. 10 thru 11C for proper wiring
sequence with conventional single boiler installations.
The THERMAL BALANCER shown is factory included by
A. O. Smith as part no. 98190. This device serves as a pump
shutdown delay switch to balance the rising boiler water
temperature to system temperature before the pump stops.
Overshooting of boiler temperature is prevented and stack loss
after shutdown is negligible.
WARNING
AN ELECTRICAL GROUND IS REQUIRED TO REDUCE RISK OF
ELECTRIC SHOCK OR POSSIBLE ELECTROCUTION. Make the
ground connection to the screw provided in the electrical supply
junction box on the boiler.
IF ANY OF THE ORIGINAL WIRE, AS SUPPLIED WITH THE
APPLIANCE,MUSTBEREPLACED,ITMUSTBEREPLACEDWITH
TYPE1050CWIREORITSEQUIVALENT,EXCEPTFORTHEFLAME
SENSOR AND IGNITION CABLE WHICH ARE 2500C AND WIRES
CONNECTED TO THE COIL PROTECTOR WHICH ARE 2000C.

1717
1717
17
CONNECTIONDIAGRAM
HWB & HW-300, -399, -420, -500 & -610
(NATURALGAS)
SINGLESTAGEI.I.D.-ROBERTSHAW®GASVALVE
HWB & HW-300, -399, -420, -520, -610 (NATURAL GAS ONLY) - CANADIAN MODELS
FIGURE10
® Robertshaw is a registered trademark of Fulton Controls Corp.

1818
1818
18
CONNECTIONDIAGRAM
HWB, HW-420,-520, -610
(PROPANEGAS)
SINGLESTAGEPROPANE -ROBERTSHAWGASVALVE
24 VOLT -HW, HWB-420, -520, -610 CANADIAN MODELS
FIGURE11

1919
1919
19
SINGLESTAGEPROPANE ROBERTSHAWGASVALVE
24 VOLT - HWB, HW-300, 399 CANADIAN MODELS
FIGURE11A
CONNECTIONDIAGRAM HWB & HW 300, 399
(PROPANEGAS)
FIGURE13

2020
2020
20
HW-300, HW-399, HW-420, HW-500 & HW-670
(NATURALGAS)
SINGLESTAGEI.I.D.-ROBERTSHAWGASVALVE
HW-300, -399, -420, -520 & 670 (NATURAL GAS ONLY) - U.S. MODELS
FIGURE11B