PEERLESS FLEX-HEAT GM Series User guide

GM™
Boilers
Series
Gas
Design &
Application
Guide

1. INTRODUCTION TO FLEX-HEAT®
MODULAR BOILER SYSTEMS 2
A. MODULAR VS. MULTIPLE..............2
B. PEERLESS®FLEX-HEAT®SYSTEM .......2
2. FLEX-HEAT®SYSTEM COMPONENTS
AND RATINGS 3
A. SERIES GM™ GAS BOILERS ............3
B. FLEX-HEAT®SEQUENCERS ............3
C. DOMESTIC WATER HEATING...........4
D. FLEX-HEAT®MANIFOLDS..............4
E. FLEX-HEAT®SYSTEM RATINGS.........4
3. MECHANICAL ROOM LAYOUT 8
A. CODE COMPLIANCE ..................8
B. GUIDELINES .........................8
4. VENTING 15
A. GENERAL ..........................15
B. SIZING GUIDE RESTRICTIONS .........16
C. VENT TERMINATION.................16
5. PIPING 25
A. PIPING ISSUES .....................25
B. AIR ELIMINATION ...................27
C. PREVENTING CONDENSATION ........29
D. COMMERCIAL SYSTEM TYPES ........31
E. DETERMINING PRESSURE DROP .......33
F. PUMP SELECTION ...................35
G. FREEZE PROTECTION ISSUES .........36
H. EXPANSION TANK SIZING ............36
6. PEERLESS®PARTNER®41
DHW SYSTEMS
A. MODELS...........................41
B. PIPING.............................41
7. GAS PIPING 43
A. CODES & STANDARDS ...............43
B. INSTALLATION GUIDELINES ..........43
C. SUPPORT THE GAS PIPING ...........44
D. GAS PIPE SIZING....................44
E. GAS PIPE SIZING EXAMPLE ...........46
8. ELECTRICAL WIRING & CONTROLS 47
A. CODES & STANDARDS ...............47
B. GENERAL GUIDELINES ...............47
TABLE OF CONTENTS
TABLE OF CONTENTS
1

The FLEX-HEAT®System consists of a wide array of
components designed to provide high energy efficiency,
simple installation, and increased comfort from your
PB Heat, LLC Series GM™ boilers.
A. MODULAR VS MULTIPLE BOILERS
The FLEX-HEAT®System is designed to be installed as a
modular boiler system as defined by ASME1:
1. Modules can be no larger than 400 mbh gas input.
All Series GM™ boilers meet this requirement.
2. No isolation or stop valves can be placed between
modules and the main headers (installation requirement).
Modular boiler systems have the advantage of requiring fewer
limit controls than multiple boiler systems. On a multiple boiler
system, two limit controls are required on each individual boiler
(Figure 1.1). On modular boiler systems, only one limit control
is required on each module and one system limit control is
required (Figure 1.2).
The FLEX-HEAT®System may be installed as either a modular
boiler system or multiple boiler system.
Low Water Cut-off(s) - The Hydrolevel Hydrostat®limit controls
used on Series GM™ boilers meet ASME1low water cut-off
requirements when used in either modular or multiple boiler
installations. The Hydrostat®controls meet ASME CSD-1 low
water cut-off requirements when set to manual reset.
B. PB HEAT, LLC FLEX-HEAT®SYSTEM
1 Modular systems have higher overall boiler plant
efficiency. (Figure 1.3).
a) Higher part load efficiency. Atmospheric gas boilers
operate most efficiently at full gas input rate. The
FLEX-HEAT®system energizes each module at its
full gas input and efficiency and instead controls
the system by modulating the number of energized
modules.
b) Lower Stand-by losses. Since the FLEX-HEAT®
system energizes only the number of modules
needed to meet the heat loss, less heat is dissipated
to the boiler room and less heat escapes up the
chimney. Primary-Secondary inatallations further
reduce stand-by losses by preventing heated water
from flowing through idle modules.
2. Modular systems are redundant. If a single boiler
installation goes down, it’s a no heat situation. On a
modular boiler system, if a single boiler shuts down, the
remaining modules will provide heat until the problem
boiler can be corrected.
3. Modular systems can be faster to maintain.
Disassembling and reassembling a large boiler to
replace a section can take a large amount of time. Since
the FLEX-HEAT®modules are pre-packaged and fit
through a standard doorway, much less time is required
to replace a module.
1. INTRODUCTION TO FLEX-HEAT®
MODULAR BOILER SYSTEMS
INTRODUCTION TO FLEX-HEAT®MODULAR BOILER SYSTEMS
2
LIMIT/
LWCO
LIMIT
MODULAR BOILER SYSTEM
Treated as if a Single Boiler
400 MBH
or Less
Input
400 MBH
or Less
Input
400 MBH
or Less
Input
LIMIT/
LWCO LIMIT/ LWCO
LIMITLIMITLIMIT
2nd Limit Required if Boilers Over 400 MBH
MULTIPLE BOILER SYSTEM
Each Unit Treated as a Separate Boiler
STOP VALVES
LIMIT/
LWCO LIMIT/ LWCO LIMIT/ LWCO
Figure 1.2: Modular Boiler System
Figure 1.1: Multiple Boiler System
1ANSI/ASME Boiler and Pressure Vessel Code, Section IV: Rules for Construction
of Heating Boilers Figure 1.3: Boiler Plant Operating Efficiency

A. SERIES GM™GAS BOILERS
1. The Series GM™ is available in four sizes suitable for
modular boiler (or multiple boiler) installations – 214.5
MBH, 268 MBH, 342 MBH and 399 MBH input
(Figures 2.1 and 2.4).
2. All controls are accessible from the front of the boiler,
and the return piping is connected to the front of the
block. This allows very close spacing of the modules
from side to side.
3. Series GM™ Gas Boilers are atmospheric design, using
a vertical draft hood (Figure 2.1).
4. The rugged design of this boiler provides wide
waterways and generous heating surface.
B. FLEX-HEAT®SEQUENCERS
1. FLEX-HEAT®sequencers are made by tekmar, a
proven leader in control design for hydronic systems,
available in two, four and eight stage versions; each
standard with outdoor reset (Figure 2.2).
tekmar
®
Eight Stage Boiler Control 258
Stage 1
Pump
Power
Stage 2
Comb. Air
WWSD
Stage 3
Setpoint TEMP ROOM OUTSIDE
UNOCC
OVR
AMPM
o o
F C
TIME
PRGM 1
2
USE
S M T W T F S
Heat
Demand
Stage 4
Minimum
Stage 5
Actual
Supply
Stage 6
Stage 7
Target
Supply
Stage 8
Override
ItemMenu Test
0.4 3.6
2.0
80
Off 170
422
120 F
o
22 F
o
Heating Curve Minimum
Boiler
Differential
Date
S/N
Power Supply: 24V 60Hz 5VA
Relay capacities: 24V 10A
Auto
Stage
12378
Stpnt
Reset
56
4
Off Off
Fixed Lead
Rotate
Lo-Hi Fire
Fixed last
Perm.
Demand
External
Demand
Int. timer
Ext. timer
tekmar®is the trade-mark of
Control Systems Ltd.,
used under license by
PB Heat, LLC
tekmar®
2. FLEX-HEAT®SYSTEM
COMPONENTS AND RATINGS
FLEX-HEAT®SYSTEM COMPONENTS AND RATINGS
3
Figure 2.2: FLEX-HEAT®Sequencer, Typical
Figure 2.1: Series GM™ Atmospheric Gas
Boiler
®SmartValve is a registered trademark of Honeywell Corporation.

C. DOMESTIC WATER HEATING
Use FLEX-HEAT®modular boilers with the Peerless®
Partner® indirect-fired water heaters for high recovery
and energy-efficient service water heating. Partner
PP models feature high grade 316L stainless steel
construction. Partner PV models feature seamless, long-life
thermoplastic construction. See Figure 2.3, 2.5, and 2.6.
D. FLEX-HEAT®MANIFOLDS
1. Optional FLEX-HEAT®manifolds provide an easy
to install piping system for parallel piping of
modular boilers.
a) The FLEX-HEAT®system uses self-retaining gaskets
and bolt-on clamps sized to adapt to 3 pipe (Figure
5.2).
b) The kits include the supply and return manifolds (for
either 2 or 3 modules) and the clamps and fittings
needed to connect from the manifolds to the boiler
supply and return connections (Figure 5.4).
E. FLEX-HEAT®SYSTEM RATINGS
FLEX-HEAT®system sizes and ratings are shown in Table 2.1.
FLEX-HEAT®SYSTEM COMPONENTS AND RATINGS
4
Figure 2.3: Peerless®Partner®Indirect-Fired
Water Heaters
(Partner PP models shown)

FLEX-HEAT®SYSTEM COMPONENTS AND RATINGS
5
Table 2.1: FLEX-HEAT®System Ratings
System
Number
Module
Quantity & Size
Input
(MBH)
Gross Output
(MBH)
Gross Output
(H.P.)
Net Output
(MBH)
FH-429 2-5 429 364 10.9 316
FH-482 1-5, 1-6 482 408 12.2 355
FH-536 2-6 536 452 13.5 394
FH-610 1-6, 1-7 610 501 15.0 436
FH-684 2-7 684 550 16.4 478
FH-741 1-7, 1-8 741 595 17.8 517
FH-798 2-8 798 640 19.1 556
FH-804 3-6 804 678 20.3 591
FH-878 2-6,1-7 878 727 21.7 633
FH-952 1-6, 2-7 952 776 23.2 675
FH-1026 3-7 1026 825 24.6 717
FH-1140 1-7, 2-8 1140 915 27.3 795
FH-1197 3-8 1197 960 28.7 834
FH-1220 2-6, 2-7 1220 1002 29.9 872
FH-1368 4-7 1368 1100 32.9 956
FH-1482 2-7, 2-8 1482 1190 35.6 1034
FH-1539 1-7, 3-8 1539 1235 36.9 1073
FH-1596 4-8 1596 1280 38.2 1112
FH-1710 5-7 1710 1375 41.1 1195
FH-1824 3-7, 2-8 1824 1465 43.8 1273
FH-1881 2-7, 3-8 1881 1510 45.1 1312
FH-1938 1-7, 4-8 1938 1555 46.5 1351
FH-1995 5-8 1995 1600 47.8 1390
FH-2052 6-7 2052 1650 49.3 1434
FH-2166 4-7, 2-8 2166 1740 52.0 1512
FH-2280 2-7, 4-8 2280 1830 54.7 1590
FH-2394 6-8 2394 1920 57.4 1668
FH-2508 5-7, 2-8 2508 2015 60.2 1751
FH-2622 3-7, 4-8 2622 2105 62.9 1829
FH-2736 1-7, 6-8 2736 2195 65.6 1907
FH-2793 7-8 2793 2240 66.9 1946
FH-2850 6-7, 2-8 2850 2290 68.4 1990
FH-2964 4-7, 4-8 2964 2380 71.1 2068
FH-3021 3-7, 5-8 3021 2425 72.4 2107
FH-3078 2-7, 6-8 3078 2470 73.8 2146
FH-3192 8-8 3192 2560 76.5 2224
FH-3306 5-7, 4-8 3306 2655 79.3 2307
FH-3363 4-7, 5-8 3363 2700 80.7 2346
FH-3420 3-7, 6-8 3420 2745 82.0 2385
FH-3534 1-7, 8-8 3534 2835 84.7 2463
FH-3591 9-8 3591 2880 86.0 2502
FH-3648 6-7, 4-8 3648 2930 87.5 2546
FH-3762 4-7, 6-8 3762 3020 90.2 2624
FH-3876 2-7, 8-8 3876 3110 92.9 2702
FH-3990 10-8 3990 3200 95.6 2780
TYPICAL FLEX-HEATbMODULAR BOILER SYSTEMS

Figure 2.4: Series GM™ Dimensions and Ratings
SERIES GM™ DIMENSIONS AND RATINGS
6
SERIES GMTM BOILER DIMENSIONS
Boiler
Model
Number
Width
“A”
Distance From Left
“B”
Height Less Vent Damper
“C”
Height With Vent Damper
“C”
Outlet Diameter
“D” *
GM-e-05 19-1/4” 9-3/4” 29” 35-7/8” 7” *
GM-e-06 22-3/4” 11-1/2” 30” 38-7/8” 8” *
GM-07 26-1/4” 13-1/4” 31” 41-7/8” 10”
GM-08 29-3/4” 15” 31” 41-7/8” 10”
* Vent Diameter is determined by outlet diameter of vent reducer (provided) installed on outlet of vent damper.
8” to 7” reducer on GM-e-05, 9” to 8” reducer on GM-e-06.
SERIES GMTM RATINGS
Boiler
Model
Number
Input,
MBH
Output1,2
MBH
Net Ratings
Water3,4,
MBH
Intermittent
Ignition
AFUE1,
%
Water
Content
(Gallons)
GM-e-05 214.5 182 158 84.2 6.15
GM-e-06 268 226 197 84.0 7.2
GM-07 342 275 239 _8.25
GM-08 399 320 278 _9.3
(1) Output is Heating Capacity for models with inputs <300 MBH and Gross Output for models with inputs ≥300 MBH. Heating Capacity and
Annual Fuel Utilization Efficiency (AFUE) ratings are based on U.S. Government test.
(2) Gross Output Rating determined in accordance with AHRI requirements.
(3) Net water ratings based on an allowance of 1.15.
(4) Consult factory before selecting a boiler for installations having unusual piping and pickup requirements, such as intermittent system operation,
extensive piping systems, etc.
*

PEERLESS®PARTNER®PP DIMENSIONS AND RATINGS
7
Figure 2.5: Peerless®Partner®PP Dimensions and Ratings
PEERLESS®PARTNER®PP DIMENSIONS
Model
Number
Dimensions Pressures (psig)
Tank Capacity
(U.S. Gallons)
Diameter Height Floor to
“Boiler In’
Floor to
“Boiler Out’
Floor to
“Cold-Drain’
Floor to
“Hot-T&P’ Test Working
PP-30-LB 23-1/4” 28-1/2” 9-3/4” 5-1/4” 5-1/4” 22” 300 150 30
PP-40 19-1/4” 52-1/2” 9-3/4” 5-1/4” 5-1/4” 46” 300 150 45
PP-60 23-1/4” 52-1/2” 9-3/4” 5-1/4” 5-1/4” 46” 300 150 60
PP-80 23-1/4” 72” 29” 6” 6” 64” 300 150 80
PP-120 27” 73-1/2” 30-1/4” 7-1/4” 7-1/4” 66” 300 150 119
PEERLESS®PARTNER®PP RATINGS AND FLOW SPECIFICATIONS
Model
Number
Peerless®Partner®Ratings Peerless®Partner®Flow Specifications
First
Hour Rating1
(Gallons)
Minimum Boiler
Output2to
Achieve First
Hour Rating
(Btu per hour)
Heat
Exchanger
Surface Area
(ft2)
Recommended
Flow Rate
Heat
Exchanger
Pressure
Drop
Domestic
Water
Connection
Sizes
140oF 115oF
PP-30-LB 169 234 114,000 15 8 gpm 6.0 ft. 3/4 NPT
PP-40 212 292 141,000 20 10 gpm 7.9 ft. 3/4 NPT
PP-60 266 370 174,000 20 10 gpm 7.9 ft. 1 NPT
PP-80 330 440 212,000 34 12 gpm 9.1 ft. 1-1/2 NPT
PP-120 423 564 269,000 34 14 gpm 11.3 ft. 1-1/2 NPT
(1) First hour rating based on heating water frim 50oF to 140/115oF with 180oF boiler water temperature. Gas- and Oil-fired and electric
water heater first hour ratings based on DOE test procedure using 90oF temperature rise (55oF to 145oF).
(2) Net I=B=R Output, Water.

Figure 2.6: Peerless®Partner®PV Dimensions and Ratings
PEERLESS®PARTNER®PV TANK DIMENSIONS
Water Heater
Model Number
Domestic Water
Connection Sizes, NPT
Boiler Connection
Sizes, NPT
Height
(to connections), Inch
Tank Diameter,
Inch
PV-40 3/4” 3/4” 40.5” 22.75”
PV-60 3/4” 3/4” 41” 28”
PV-80 1-1/2” 1” 53.5” 28”
PV-120 1-1/2” 1” 74” 28”
PEERLESS®PARTNER®PV DIMENSIONS AND RATINGS
TOP VIEW
45.00°
FRONT
HX IN
COLD IN
HOT OUT
HX OUT
PARTNER
PEERLESS®PARTNER®PV RATINGS
Water
Heater
Model
Number
Potable
Water
Volume,
gallons
Standby
Loss,
oF/h
Continuous
Draw,
gal/h
First Hour
Rating,
gal/h
Min Heat
Source
output,
MBH
Min Heat
Source
Flow,
gpm
Heat Source
Friction
Loss,
Feet w.c.
PV-40 30.0 0.8 177 199 115000 8.0 18.7
PV-60 55.0 0.6 177 217 115000 8.0 18.7
PV-80 80.0 0.4 315 381 199000 14.0 16.0
PV-120 119.0 0.4 381 477 244000 14.0 20.0
These ratings were obtained with a heat source output and heat source flow rate as listed in the chart using the
parameters of the Domestic Cold Water inlet at 58oF , Domestic Temperature Rise of 77oF and Boiler Temperature
Output of 180oF. Other results will be obtained under differenct conditions.
8

A. CODE COMPLIANCE
1. The suggestions in this Guide are based primarily
on the National Fuel Gas Code, ANSI Z223.1 and
ASHRAE recommendations for piping, etc.
2. The guidelines for installation and control of the
equipment are consistent with the ASME Code Section
IV. Where ASME CSD-1 compliance is required, be
sure to utilize manual reset limits and low water cut-offs
as required.
3. Make sure that the final design and execution of the
modular boiler installation complies with all applicable
local codes and jurisdictions.
B. GUIDELINES
1. Air Openings: Provide air openings for combustion
and ventilation as required by ANSI Z223.1 and local
requirements (Figures 3.1, 3.6 and 3.7).
a) Required Combustion Air Volume: The total
required volume of indoor air is to be the sum of the
required volumes for all appliances located within
the space. Rooms communicating directly with the
space in which the appliances are installed and
through combustion air openings sized as indicated
in this section are considered part of the required
volume. The required volume of indoor air is to be
determined by one of two methods.
1. Standard Method: The minimum required
volume of indoor air (room volume) shall be 50
cubic feet per 1000 BTU/Hr (4.8 m³|kW). This
method is to be used if the air infiltration rate is
unknown or if the rate of air infiltration is known
to be greater than 0.6 air changes per hour. As
an option, this method may be used if the air
infiltration rate is known to be between 0.6 and
0.4 air changes per hour. If the air infiltration
rate is known to be below 0.4 then the Known
Air Infiltration Rate Method must be used. If the
building in which this appliance is to be installed
is unusually tight, PB Heat, LLC recommends
that the air infiltration rate be determined.
2. Known Air Infiltration Rate Method: here
the air infiltration rate of a structure is known,
the minimum required volume of indoor air for
appliances other than fan assisted and for the
Series GM™ Boiler shall be determined as follows:
21 ft3 Iother
Required Volumeother =
( )
ACH 1000
Btu|hr
where:
Iother = Input of appliances other than fan
assisted in Btu/hr
ACH= air change per hour (percent of the
volume of the space exchanged per
hour, expressed as a decimal)
3. MECHANICAL ROOM LAYOUT
MECHANICAL ROOM LAYOUT
9
Figure 3.1: Provide Air Openings for
Combustion and Ventilation Air
Figure 3.2: Consider Minimum Centers for
Vent System when Laying Out
Boiler Plan

MECHANICAL ROOM LAYOUT
10
For fan assisted appliances, calculate the required
volume of air using the following equation:
15 ft3 Ifan
Required Volumefan =
( )
ACH 1000
Btu|hr
Ifan = Input of the fan assisted appliances in
Btu/hr
Note: These calculations are not to be used for
infiltration rates greater than 0.60 ACH.
b) Combination Indoor and Outdoor Combustion Air:
If the required volume of indoor air exceeds the
available indoor air volume, outdoor air openings
or ducts may be used to supplement the available
indoor air provided:
1. The size and location of the indoor openings
comply with Figure 3.6.
2. The outdoor openings are to be located in
accordance with Figure 3.7.
3. The size of the outdoor openings are to be sized
as follows:
where:
Areq = minimum area of outdoor openings.
Afull = full size of outdoor openings calculated
in accordance with Figure 3.7.
Vavail= available indoor air volume
Vreq = required indoor air volume
2. Boiler Room Pressure: The boiler room must at all
times be neutral or slightly positive pressure relative to
the outside. Otherwise the vent system will not work
and flue gas will spill into the building.
3. Wiring: DO NOT run electrical wiring conduits under
the boiler slab area. The temperature will be too high,
likely to cause wiring failures.
4. Vent System Spacing
a) Consider the minimum required spacing between
tees for the vent system when laying out the boiler
plan (Figure 3.2).
b) Note that FLEX-HEAT®manifolds position modules
on 32” centers. When the modules are vented with a
combined vent larger than 20 inch diameter it may
not be possible to use FLEX-HEAT®manifolds
because the spacing may be too close for B vent
(Venting Section Table 4.1).
5. Combustible Flooring: The Series GM™ boiler is NOT
suitable for mounting on combustible flooring. If it is
necessary to build a non-combustible floor pad over
top of an existing combustible floor, construct pad as
stated in the National Fuel Gas Code Handbook Part 6,
Installation of Specific Equipment.
6. See Figures 3.3 and 3.4 for typical mechanical
room lay-out.
7. See Figure 3.5 for clearances to combustible
construction and for accessibility.
Vavail
1 –
Vreq
Areq = Afull
(
(

MECHANICAL ROOM LAYOUT
11
Figure 3.3: Typical Mechanical Room Layout with Four Modules and Individual Venting

MECHANICAL ROOM LAYOUT
12
Figure 3.4: Typical Mechanical Room Layout with Four Modules and Manifolded Vent

MECHANICAL ROOM LAYOUT
13
Access Clearance
(24" Recommended)
Access Clearance
(24ì Recommended)
Access Clearance
(24ì Recommended)
Access Clearance
(24" Recommended)
Access Clearance
(24" Recommended)
Access Clearance
(24" Recommended)
Access Clearance
(24" Recommended)
Ceiling height must
provide space for
combined vent
breeching and minimum
connector rise (height
from draft hood outlet
to center of breeching)
Front Front
Rear
Rear
Side
Rear
30"
Front of Jacket to Wall or Other Obstruction
30"
Access Clearance
(24" Recommended)
TYPICAL LAYOUT
10 MODULES SHOWN
When Using FLEX-HEAT Manifolds
32"
CLEARANCE REQUIREMENTS
CLEARANCE TO COMBUSTIBLE CONSTRUCTION:
From SIDES of modules: Minimum 6 inches From REAR of modules: Minimum 6 inches From Draft Hood, Flue Pipe, Hot Water Pipes: Minimum 6 inches Over Top of Jacket: Minimum 36 inches Modules are CSA design certified for alcove
(2 inches between modules)
The clearances shown in the illustrations below and right are general guidelines for access and service. Adhere to local code
requirements.
Figure 3.5: Clearances to Combustible Construction and for Accessibility

MECHANICAL ROOM LAYOUT
14
Boilers located in space with less volume than what is required by 3.B.1.a
Two air openings may be used:
openings must connect spaces on same floor each opening must provide a free area of at least 1 square inch per 1000 Btuh of all appliances in the space one opening must be located within 12 inches of the ceiling; the other within 12 inches of the floor
One or more openings may be used:
openings must connect spaces on different floors total free area of openings must be at least 2 square inches per 1000 Btuh of all appliances in the space
Figure 3.6: Provide Combustion/Ventilation Air Openings as Required by Codes.

MECHANICAL ROOM LAYOUT
15
Air openings must be taken from outside when:
The total volume of the building is less than what is required by 3.B.1.a. The building is under a negative pressure or must be isolated for any reason from the boiler room
Two air openings may be used:
If Direct to outside or through Vertical Ducts: each opening must provide a free area of at least 1 square inch per 4000 Btuh of all appliances in the space If through Horizontal Ducts: each opening must provide free area of at least 1 square inch per 2000 Btuh of all appliances in the space One opening must be located within 12 inches of the ceiling; the other within 12 inches of the floor
One air opening may be used:
Opening in wall, horizontal or vertical duct may be used Opening must provide a free area of at least 1 square inch per 3000 Btuh of all appliances in the space and not less than the cross-sectional area of vent connectors of all appliances in the space All appliances must have clearances of at least 1 inch from the sides and back and 6 inches from the front Opening must begin within 12 inches of the top of the space
Figure 3.7: Provide Combustion/Ventilation Air Openings as Required by Codes. Openings Must
Connect to Outside if the Total Volume of All Interconnected Indoor Spaces is Less
Than What is Required by 3.B.1.a.

VENTING
16
A. GENERAL
1. Vent construction - National Fuel Gas Code
Requirements
a) The National Fuel Gas Code requirements for
venting have changed significantly. National
laboratories and research groups have concentrated
for some time on problems of condensation and
poor draft in over-sized vent systems.
b) The most noticeable changes are in the restriction on
size of the vent versus the size of the smallest
connected appliance draft hood. The National Fuel
Gas Code, ANSI Z223.1, restricts the vent cross
sectional area to no more than 7 times the area of
the smallest appliance draft hood outlet connected
to the vent (paragraph 13.2.17, “Vertical Vent Size
Limitation”).
c) Exterior masonry chimneys must be lined with a
metal chimney liner. Without a lining these chimneys
will condense (causing mortar deterioration) and
possibly not develop a draft (causing spillage).
d) Single wall vent is more prone to condensation than
B vent, so the new vent tables are more restrictive
in the application of single wall vent. The vent sizing
information in this Guide is based on type B vent.
Consult the factory or apply the National Fuel Gas
Code tables where single wall vent is to be used.
e) The suggestions for venting in this Guide are based
on the vent tables and notes in the 2006 edition of
the National Fuel Gas Code, ANSI Z223.1. As
allowed in the Code, other vent system designs
may be specially engineered using accepted
engineering practices.
f) Because of the limitations of single wall vent, this
Guide focuses mostly on type B vent applications.
For use of single wall vent or masonry construction
refer to local codes and/or the National Fuel Gas
Code, ANSI Z223.1.
2. Boiler Spacing - Vent Considerations
a) See Table 4.1 for typical limitations on spacing of
adjacent modules when using B vent. This table
is based on data taken from one manufacturers
vent instructions.
b) Note that FLEX-HEAT®manifolds are only available
for 32-inch centers. When the modules are vented
with a combined vent larger than 20 inch diameter it
may not be possible to use FLEX-HEAT®manifolds
because the spacing would be too close for B vent (if
the dimensions of fittings are as shown here).
3. Vent Priming - Consider Sequence
a) We recommend always beginning the sequence with
the module(s) closest to the vertical vent. This will
assure better priming of the vent system.
b) If using a sequencer which rotates the sequence, set
the module closest to the vent to always come on
first and rotate the rest.
4. VENTING
Table 4.1: Minimum Module Center to Center Spacing Based on One Manufacturer’s
Vent Tee Data

VENTING
17
B. SIZING GUIDE RESTRICTIONS
1. No other appliances can be connected to the vent when
using the sizing information in this Guide.
2. Where the mechanical room does not have enough
height for manifolded venting as suggested in this
Guide the vent system may need to be custom
engineered for application of a draft inducer sized and
applied for the application by others.
3. The boiler room must be under a neutral or slightly
positive pressure – never negative.
a) The boiler room MUST meet this criteria in order to
use atmospheric gas boilers.
b) If the negative pressure is due to the pressure in the
building, isolate the boiler room securely so proper
conditions can be maintained.
c) Do not use exhaust fans in the building or boiler
room which could operate while the boilers are in
operation unless the application is custom
engineered and the air openings are enlarged
adequately to eliminate the possibility of negative
pressure in the room.
4. The vent sizing information in the manual does not
allow for offsets in the vertical vent section. If the
vertical vent is offset, reduce the vent capacity by 20%
for each set of 90 degree elbows in the offset or 10%
for each set of 45 degree elbows in the offset
(Figure 4.1).
5. The vent tables in this guide apply to interior chimneys.
See National Fuel Gas Code for sizing guidelines when
using exterior chimney(s).
6. The National Fuel Gas Code states that the vent tables
do not apply when vent dampers are used. When
using vent dampers and a tile-lined masonry chimney,
close attention must be paid to the potential for
condensation. Exterior masonry chimneys must have
an approved metal liner when using vent dampers.
7. Corrugated chimney liners:
a) When using corrugated metal lining in the chimney
reduce vent capacity shown in these tables by 20%.
b) If offset, use an additional reduction of 10%
per 90 degree elbow, 5% per 45 degree
elbow equivalent.
8. High altitude applications: Use sea level input ratings
to determine maximum capacity for high altitude
installation. Use actual input (derated for altitude)
to determine minimum capacity for high altitude
installation. See National Fuel Gas Code for minimum
capacity requirements.
C. VENT TERMINATION
1. Always use a vent cap to reduce wind effects and
downdrafts (Figure 4.2).
Figure 4.2: Vent Termination
Figure 4.1: Reduce Vent Capacity if Vertical
is Offset Rather Than Straight Up

VENTING
18
Figure 4.3: Individual Venting – See Table for Vent Sizing

Table 4.2: Individual Vent Sizing Using Type B Vent or Single Wall Metal Pipe
VENTING
19
VENT SIZING TABLE - GMTM MODULAR
Individual Venting
GM-e-05 GM-e-06
214.5 268
78