lntellihot iQ251 User manual

Operation & Installation Manual
iQ251, Gen II
WARNING
If the information in these instructions is not followed
exactly, a re or explosion could result causing
property damage, personal injury, or death.
— Do not store or use gasoline or other ammable
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.
• If you cannot reach your gas supplier, call the
re department.
— Installation and service must be performed by
a qualied installer, service agency, or the gas
supplier.
— Ne pas entreposer ni utiliser d’essence ou
ni d’autres vapeurs ou liquides inammables
à proximité de cet appareil ou de tout autre
appareil.
QUE FAIRE SI VOUS SENTEZ UNE ODEUR DE GAZ
• Ne pas tenter d’allumer d’appareil.
• Ne touchez à aucun interrupteur; ne pas vous
servir des téléphones se trouvant dans
le bâtiment.
• Appelez immédiatement votre fournisseur de gaz
depuis un voisin. Suivez les instructions
du fournisseur.
• Si vous ne pouvez rejoindre le fournisseur,
appelez le service des incendies.
— L’installation et l’entretien doivent être assurés
par un installateur ou un service d’entretien
qualié ou par le fournisseur de gaz.
AVERTISSEMENT
Assurez-vous de bien suivre les instructions données
dans cette notice pour réduire au minimum le
risque d’incendie ou d’explosion ou pour éviter tout
dommage matériel, toute blessure ou la mort.

Thank you for purchasing this Intellihot unit.
This unit is designed for years of trouble free operation, and I urge you to read and follow the
instructions in this “Operation & Installation Manual.”
Our mission to create a better heating system began back in the winter of 2005 when a tank
water heater broke down and ooded my basement. By combining the principles of a diesel
engine’s robustness, robotics intelligence, and marine environment durability, we set out to
design a unit from the ground up that would outperform and outlast all others.
Quickly, our goal grew from not just making a better water heater, but creating an intelligent
water heating and delivery system. Innovation is our hallmark and simplicity, eciency, and
durability are at the core of every lntellihot product.
Our products are proudly engineered and built in Galesburg, Illinois. lntellihot has helped
commercial customers throughout the nation save thousands of dollars while eliminating
downtime. Our talented team of dedicated professionals is ready to assist you and help your
business succeed.
I thank you for purchasing our lntellihot products.
Sincerely,
Sri Deivasigamani
CEO, lntellihot Inc.

3iQ251
Jan 2021 - Revision 02
Table of Contents
1. General Information
1.1 Items Shipped With Water Heater. . . . . . . . . . 5
1.2 Serial Number Plate Locations . . . . . . . . . . . . 5
2. Safety
2.1 Safety Signal Words. . . . . . . . . . . . . . . . . . . . . 6
2.2 Installation Warnings . . . . . . . . . . . . . . . . . . . . 6
3. Technical Specications
3.1 Specications Chart . . . . . . . . . . . . . . . . . . . . 8
3.2 High Elevation Installations . . . . . . . . . . . . . . . 8
3.3 Clearance Requirements . . . . . . . . . . . . . . . . . 9
3.4 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.5 Exhaust Gas Standards . . . . . . . . . . . . . . . . . . 9
3.6 Dimensional Specications . . . . . . . . . . . . . . 10
4. Preparation Before Installation
4.1 Selecting an Indoor Installation Site . . . . . . . . 11
4.2 Selecting an Outdoor Installation Site . . . . . . 12
5. Wall Mounting
5.1 Mounting the Unit to the Wall . . . . . . . . . . . . 13
6. Gas Connection
6.1 Quick Reference Installation Instructions . . . 14
6.2 Fuel Source . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.3 Gas Pressure Requirements . . . . . . . . . . . . . 14
6.4 Gas Pressure Regulator . . . . . . . . . . . . . . . . . 14
6.4.1 Venting of Gas Supply Regulators . . . 14
6.5 Length of Gas Supply Pipe . . . . . . . . . . . . . . 14
6.6 Gas Piping Material . . . . . . . . . . . . . . . . . . . . 15
6.7 Determine Correct Gas Pipe Diameter . . . . . 15
6.8 Gas Pipe Drip Leg and Shut-oValve . . . . . . 15
6.9 Gas Pipe Sizing Tables . . . . . . . . . . . . . . . . . . 16
7. Air Intake Inlet and Exhaust Gas Outlet Pipe
Connections
7.1 Quick Reference Installation Guide . . . . . . . . 18
7.2 Typical Single Unit Air Intake Inlet and
Exhaust Gas Outlet Pipe Installation . . . . . . . 18
7.3 Two Pipe Vent System (Direct Vent) . . . . . . 19
7.3.1 Single Unit Congurations . . . . . . . . . 19
7.3.2 Multiple Units Congurations . . . . . . . 20
7.3.3 Side Wall Air Intake Inlet and Exhaust
Gas Outlet Pipe Termination. . . . . . . . 20
7.3.4 Roof Air Intake Inlet and Exhaust Gas
Outlet Pipe Termination . . . . . . . . . . . 21
7.4 Single Pipe Venting System (Power Vent) . . 21
7.4.1 Single Unit . . . . . . . . . . . . . . . . . . . . . . 21
7.4.2 Multiple Units . . . . . . . . . . . . . . . . . . . 22
7.4.3 Concentric Venting Termination
(Single Unit) . . . . . . . . . . . . . . . . . . . . 22
7.4.4 Concentric Venting Termination
(Multiple Units) . . . . . . . . . . . . . . . . . . 23
7.5 Intake Air Requirements . . . . . . . . . . . . . . . . 24
7.6 Intake Air Inlet and Exhaust Gas Outlet Pipe
Diameter and Length . . . . . . . . . . . . . . . . . . . 24
7.7 Venting Clearance Specications . . . . . . . . . 25
7.8 Exhaust Gas Outlet Pipe Materials . . . . . . . . 26
7.9 Air Intake Inlet Pipe Vent Materials . . . . . . . . 26
7.10 Recommended Exhaust Gas Outlet Pipe
Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8. Water Connections
8.1 Quick Reference Installation Instructions . . . 28
8.2 Hot Water Connection . . . . . . . . . . . . . . . . . . 28
8.3 Cold Water Connection . . . . . . . . . . . . . . . . . 29
8.4 Condensate Drain Line . . . . . . . . . . . . . . . . . . 29
8.5 External Recirculation Options . . . . . . . . . . . 31
9. Electrical
9.1 Electrical Code Requirements . . . . . . . . . . . . 33
9.2 Electrical Connection and Polarity. . . . . . . . . 33
10. Adjusting CO2Level
10.1 General Information . . . . . . . . . . . . . . . . . . . . 34
10.2 Adjustment Procedure . . . . . . . . . . . . . . . . . . 34
11. Natural Gas to Propane Conversion
11.1 General Information . . . . . . . . . . . . . . . . . . . . 37
11.2 Conversion Procedure . . . . . . . . . . . . . . . . . 37
12. Operation
12.1 Control Panel . . . . . . . . . . . . . . . . . . . . . . . . . 39
12.2 Turning Water Heater ON and OFF . . . . . . . . 39
12.3 Setting the Time . . . . . . . . . . . . . . . . . . . . . . 40
12.4 Adjusting the Water Temperature . . . . . . . . . 40
12.5 Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
12.5.1 Setting Passcode Protection . . . . . . . 41
12.5.2 Forgot Passcode . . . . . . . . . . . . . . . . . 41
12.6 iNTouch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
12.7 Life Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
12.8 Unit Information . . . . . . . . . . . . . . . . . . . . . . . 42
12.9 More Screens. . . . . . . . . . . . . . . . . . . . . . . . . 43
12.9.1 Wi-Fi . . . . . . . . . . . . . . . . . . . . . . . . . . 43
12.9.2 Error History . . . . . . . . . . . . . . . . . . . . 43
12.9.3 telliCare Service (Subscribe at Startup) 44
13. Connecting Multiple Units
13.1 General Information . . . . . . . . . . . . . . . . . . . . 46
13.2 Installation Procedure . . . . . . . . . . . . . . . . . . 46
13.2.1 telliCare for Multiple Units . . . . . . . . . 48
14. Maintenance
14.1 Cleaning the Inlet Water Strainer . . . . . . . . . 49
14.2 Draining the Water Heater . . . . . . . . . . . . . . . 49
14.3 Filling the Water Heater . . . . . . . . . . . . . . . . . 50
15. Wiring Diagrams and Troubleshooting
15.1 Operational Flow Chart . . . . . . . . . . . . . . . . . 51
15.2 Complete Wiring Diagram (all models) . . . . . 52
15.3 Troubleshooting Guide. . . . . . . . . . . . . . . . . . 53
16. Serviceable Parts
16.1 Electrical Components . . . . . . . . . . . . . . . . . 56
16.2 Water Lines and Fittings . . . . . . . . . . . . . . . . 57
16.3 Blower, and Gas Valve. . . .. . . .. . . .. . . . . . . . 58
16.4 Exhaust and Air Intake . . . . . . . . . . . . . . . . . . 59
16.5 Miscellaneous . . . .. . . . . . . . . . . . . . . . . . . . . . 60
17. Requirements for State of Massachusetts
17.1 Notice Before Installation . . . . . . . . . . . . . . . 61
18. Warranty
18.1 Warranty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
19. Product Warranty
19.1 Warranty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

iQ251 4
May 2018 - Revision 01
DANGER
To avoid product damage, personal injury, or
evenpossible death, carefully read, understand,
and follow all the instructions in this Operation
and Installation Manual before installing this
product. Improper installation, adjustment, alteration,
or maintenance can cause injury, loss of life, and/or
property damage. This water heater should be installed
and serviced by a qualified technician. The lack of
proper service can result in a dangerous condition.
Due to Intellihot’s policy of continuous product improvement
and technology, the design and/or technical specifications in
this manual are subject to change without notice.
This manual contains safety information, installation
instructions, and maintenance procedures. It must be left
with the homeowner or placed near the water heater in a
noncombustible location. The customer should retain this
manual for future reference.
This product complies with ANSIZ21.10.3 (2011) / CSA 4.3 Gas Water Heater. For use as potable water heating.
Certified to
NSF/ANSI 372
Contact Information
Call us, your dealer, first if you have any questions about this
product. We can help answer questions about installation,
operation, or if there are damaged or missing parts when
unpacking this unit from the shipping box.
Dealer Contact Information.
WARNING
If the information in these instructions is not followed
exactly, a re or explosion could result causing
property damage, personal injury, or death.
— Do not store or use gasoline or other ammable
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.
• If you cannot reach your gas supplier, call the
re department.
— Installation and service must be performed by
a qualied installer, service agency, or the gas
supplier.
— Ne pas entreposer ni utiliser d’essence ou
ni d’autres vapeurs ou liquides inammables
à proximité de cet appareil ou de tout autre
appareil.
QUE FAIRE SI VOUS SENTEZ UNE ODEUR DE GAZ
• Ne pas tenter d’allumer d’appareil.
• Ne touchez à aucun interrupteur; ne pas vous
servir des téléphones se trouvant dans
le bâtiment.
• Appelez immédiatement votre fournisseur de gaz
depuis un voisin. Suivez les instructions
du fournisseur.
• Si vous ne pouvez rejoindre le fournisseur,
appelez le service des incendies.
— L’installation et l’entretien doivent être assurés
par un installateur ou un service d’entretien
qualié ou par le fournisseur de gaz.
AVERTISSEMENT
Assurez-vous de bien suivre les instructions données
dans cette notice pour réduire au minimum le
risque d’incendie ou d’explosion ou pour éviter tout
dommage matériel, toute blessure ou la mort.

5 iQ251 General Information
May 2018 - Revision 01
1. General Information
1.1 Items Shipped With Water Heater
The following items are shipped with the water heater.
Temperature and
Pressure Relief Valve
(must be installed)
Condensate
Drain
(see Warning)
Operation & Installation
Manual
Communication Cable
Wall Mounting
Bracket
Operation & Installation Manual
iQ251, Gen II
WARNING
Ifthe information in these instructionsisnotfollowed
exactly, a or explosion couldresult causing
propertydamage, personal injury, or death.
— Donot store or usegasoline or other
vaporsand liquids in the vicinityof this orany
otherappliance.
WHATTO DO IFYOU SMELL GAS
•
Donot tryto light any appliance.
•
Donot touch any electrical switch; do not use
anyphone in your building.
•
Immediately call your gas supplierfrom a
neighbor’s phone. Follow the gassupplier’s
instructions.
•
Ifyoucannot reach your gassupplier,call the
department.
—Installation and service must be performed by
a installer,service agency, or the gas
supplier.
—Ne pas entreposer ni u
tiliser d’essence ou
ni d’autresvapeursou liquides
à proximité de cet appareil ou de toutautre
appareil.
QUEFAIRESIVOUSSENTEZUNEODEUR DE GAZ
•
Nepastenter d’allumer d’appareil.
•
Netouchezà aucun interrupteur;nep
asvous
servir des téléphones se trouvant dans
lebâtiment.
•
Appelezimmédiatement votre fournisseur de gaz
depuisun voisin. Suivez les instructions
dufournisseur.
•
Sivous ne pouvezrejoindre le fournisseur,
appelezle service des incendies.
—
L’installationet l’entretien doiventêtre assurés
parun installateur ou un service d’entretien
oupar le fournisseur de gaz.
AVERTISSEMENT
Assurez-vousdebiensuivreles instructions données
dans cette noticepour réduire auminimum le
risqued’incendie ou d’explosionou pour évitertout
dommagematériel, touteblessureou la mort.
WARNING
The condensate drain line is shipped from the
factory with a loop held together with plastic
ties. Do not remove the ties and/or straighten
the loop. This loop forms an air block (trap)
which prevents carbon monoxide from exiting the water
heater through the drain line. Improper installation of
the drain line can result in excessive levels of carbon
monoxide, which can lead to severe personal injury or
death.
1.2 Serial Number Plate Locations
The unit’s serial number is located on the rating plate on
the side panel of the unit. Please provide this serial number
when inquiring about service or warranty solutions. Each
heat engine also has a serial number located on its ASME
certification tag.
Heat Engine (ASME) Serial Number: ________________
Date of Installation: ___ / ___ / ______

iQ251 Safety 6
May 2018 - Revision 01
2. Safety
2.1 Safety Signal Words
DANGER
Indicates an imminently hazardous situation which, if
not avoided, will result in death or serious injury. This
signal word is limited to the most extreme situations.
WARNING
Indicates a potentially hazardous situation which, if not
avoided, could result in death or serious injury.
CAUTION
Indicates a potentially hazardous situation which, if not
avoided, may result in minor or moderate injury.
NOTICE
Indicates that equipment or property damage can result if
instructions are not followed.
SAFETY
INSTRUCTIONS
Safety instructions (or equivalent) signs indicate
specific safety-related instructions or procedures.
Note: Contains additional information important to a
procedure.
2.2 Installation Warnings
WARNING
DO NOT use this water heater for any purpose other
than water heating.
Read, understand, and follow the Installation and Operation
Manual, including all warnings and precautions, before
operating this water heater. If you do not follow these
instructions exactly, a fire or explosion may result, causing
property damage, personal injury, or loss of life.
Follow all local codes and the most recent edition of the
National Fuel Gas Code (ANSI Z223.1/NFPA 54) in the USA
or the Natural Gas and Propane Installation Code in Canada
(CSA B149.1).
This water heater must be installed by a licensed plumber,
gas fitter, and/or professional service technician. Installation
by unqualified person(s) voids the warranty.
DANGER
A. This water heater does not have a pilot. It is equipped
with an ignition device which automatically lights the
burner. Do not try to light the burner manually.
B. BEFORE OPERATING, smell all around the water
heater area for gas. Be sure to smell next to the floor
because some gas is heavier than air and will settle
on the floor.
WHAT TO DO IF YOU SMELL GAS:
• Do not try to light any appliance.
• Donot touch any electricswitch; do not use any phone in
your building.
• Immediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
• If you cannot reach your gas supplier, call the fire or
police department.
C. Use only your hand to turn the manual gas shut-off
valve. Never use tools. If manual gas shut-off valve will
not turn by hand, don’t try to repair it. Call a qualified
service technician. Force or attempted repair may
result in a fire or explosion.
WARNING
DO NOT use or store flammable liquids around the water
heater, including gasoline, oils, spray paints, etc.
DO NOT operate this water heater unless it is properly
vented to the outside (the exhaust vent piping must be
connected from the unit directly to the outside). Improper
venting can cause a build-up of carbon monoxide, which
can result in brain damage or death. Exhaust gases must
be completely expelled out of the building.
This water heater is factory preset for NATURAL GAS
but may be field converted for use with propane.
For propane conversion, refer to the Propane (LPG)
Conversion section of this manual. Connecting the
water heater to any other gas supply can result in
property damage, serious injury, or even death.
This water heater is suitable for use in potable water
heating applications. The cold and hot water fittings on
the top of the water heater MUST NOT be connected to
any heating system.
The water heater temperature is factory set to 120°F
(49°C). Hot water temperatures above 125°F can cause
severe burns instantly or death from scalds. If the
proposed water heater outlet temperature is to be set
above 125°F, installation of a thermostatically controlled
(or temperature limiting) mixing valve is recommended
for all hot water going to faucets to avoid the risk
of scalding. Examples include commercial applications
where 140°F (60°C) is often needed or if the space
heating temperature required is higher than the domestic
hot water. Always check the temperature of the hot
water before bathing, showering, washing, etc.

7 iQ251 Safety
May 2018 - Revision 01
Protect against snow and debris accumulation around
the vent terminations. Regularly inspect the exhaust
vent pipe and the air intake pipe to ensure they remain
clear from obstructions at all times.
CAUTION
Make sure you know the location of the gas shut-off
valve and how to operate it. Immediately close the
gas shut-off valve if the water heater is subjected to
fire, overheating, flood, physical damage, or any other
damaging condition that might affect the operation of
the unit. Have the water heater checked by a qualified
technician before resuming operation.
If the water quality is known to have high acidity and/
or high hardness, water treatment is recommended.
Consult the local water authority.
SAFETY
INSTRUCTIONS
DO NOT use this appliance if any part has been under
water.
DO NOT reverse the cold water and gas connections as
this will damage the gas valve.
DO NOT over-tighten fittings as damage may occur,
causing internal leakage.
The appliance should be located in an area where leakage
within the unit or at its connections will not result in
damage to the surrounding area. The manufacturer
will not be responsible for any damage resulting from
leaking if adequate drainage is not provided.

iQ251 Technical Specifications 8
May 2018 - Revision 01
3. Technical Specifications
3.1 Specifications Chart
iQ251 Series Gen II Specifications
Technical Data Specification
Type Indoor/Outdoor, Wall Hung, Fully Condensing, On-demand Water Heater
Fuel Preset for natural gas but convertible to propane
Minimum / Maximum Input (BTUs/hour) 30,000 / 251,000
Thermal Efficiency 96%
Dimensions H X W X D (inches) 26.4 X 17.8 X 15 (3.9 cu. ft)
Weight (lbs) 90
Water Inlet / Outlet Connection 3/4” NPT
Gas Inlet Connection 3/4” NPT
Minimum Flow Rate for Activation 0.6 GPM
Ignition Electronic Spark Ignition
Venting Type Direct Vent (2 pipe – air intake and exhaust gas outlet),
Power Vent (1 pipe – exhaust gas only)
Venting Material Options Sch. 40 PVC, Sch. 40 CPVC, Polypropylene, Stainless Steel (AL29-4C)
Max 3” Air Inlet and Exhaust Gas Outlet Pipe Length – Single Pipe / Power
Vent
130 ft; deduct 5 ft per 90° elbow and 2 ft per 45° elbow
Max 3” Air Inlet and Exhaust Gas Outlet Pipe Length – Two Pipe / Direct
Vent
65 ft; deduct 5 ft per 90° elbow and 2 ft per 45° elbow
Common Venting for Multiple Units Yes
Safety Features Flame Rod, Thermal Fuse, Overheat Prevention Device, Fan Speed Monitor,
Flue Temperature Monitor, Blocked Vent Detector, Water Shut-Off Valve,
two 10A Fuses, Dual Flame Sensing, Flue Damper
Water Pressure Min / Max (PSI) 30/160
Natural Gas and Propane – Minimum Static Gas Pressure 1/2” Pipe 6” W.C. (non-corrugated, black iron)
Natural Gas and Propane – Minimum Static Gas Pressure 3/4” Pipe 2.5” W.C. (non-corrugated, black iron)
Natural Gas and Propane – Maximum Static Gas Pressure 14” W.C.
Gas Pressure for Adjustments 8” W.C. for natural gas and 11” W.C. for propane
Electrical Requirements 120V AC, 60 Hz, 15 Amp Circuit Breaker
Power Consumption 500W (Max 4.2 Amps), 8W (Standby)
Features Specification
Certification Organizations ETL (Z21.10.3 / CSA 4.3), ASME HLW
Cascading Masterless, up to 10 units
Heat Engine Expandable, Stainless 316L
Performance Specification
Hot Water Output (35°F Rise) 13.8 GPM (for installations above 2,000 feet see section 3.2)
Hot Water Output (45°F Rise) 10.7 GPM (for installations above 2,000 feet see section 3.2)
Hot Water Output (77°F Rise) 6.3 GPM (for installations above 2,000 feet see section 3.2)
Domestic Mode Water Temperature Settings 100 – 140°F
Commercial Mode Water Temperature Settings 100 – 190°F
Warranty (with recirculation, and unlimited thermal cycles) Heat Engine Coil – 10 years, All Other Parts – 2 years
Note: Due to continuous product improvements, the design and technical specifications are subject to change without notice.
3.2 High Elevation Installations
For operation at elevations above 2,000 feet, the hot water
delivery output should be reduced by 4% for each 1,000 feet
above sea level.

9 iQ251 Technical Specifications
May 2018 - Revision 01
3.3 Clearance Requirements
In order for the water heater to operate properly and
efficiently, the clearances specified in the table are required.
Location
Required Recommended
From
Combustibles
From Non-
Combustibles
Service
Clearance1
Top 6” (15.2 cm) 2” (50.8 cm) 12” (30.4 cm)
Back25/8” (15.8 mm) 5/8” (15.8 mm) 5/8” (15.8 mm)
Sides 1” (25.4 mm) 1/2” (12.7 mm) 1” (25.4 mm)
Front 2” (5.1 cm) 2” (5.1 cm) 30” (76.2 cm)
Bottom 12” (30.4 cm) 12” (30.4 cm) 12” (30.4 cm)
1Service clearances are suggested to allow for normal service.
2Mounting bracket automatically sets this distance.
3.4 Connections
Connections
Item Description Specification1
1 Hot Water Outlet Connection 3/4” Female NPT
2 Exhaust Gas Vent 3” O.D.
3 Gas Supply Inlet Connection 3/4” Female NPT
4 Gas Pressure Analyzer Port 1/8” Female NPT
5 Fresh Air Intake 3” O.D.
6 Access Ports for Blower Mounting
Screws
—
7 Cold Water Inlet Strainer —
8 Cold Water Inlet Connection 3/4” Male NPT
9 Power Supply Cord and Plug 120V AC Power
10 Condensate Drain Connection 3/4” Nipple (3/4” flex
hose)
1Using sizes other than specified can cause damage to the water
heater and will void the warranty.
3.5 Exhaust Gas Standards
CO2and CO Standards
Description CO2Range (%) Max. CO Level (ppm)
Natural Gas
High Fire 9.1% to 9.3% < 200 ppm
Low Fire 9.1% to 9.3% < 60 ppm
Propane Gas
High Fire 10.1% to 10.5% < 200 ppm
Low Fire 10.1% to 10.5% < 60 ppm

iQ251 Technical Specifications 10
May 2018 - Revision 01
3.6 Dimensional Specifications
[380]
15.0

11 iQ251 Preparation Before Installation
May 2018 - Revision 01
4. Preparation Before Installation
4.1 Selecting an Indoor Installation Site
Note: When installing the water heater, follow all local
building codes and the current edition of the National
Fuel Gas Code (ANSI Z223.1/NFPA 54) in the USA,
or National Gas and Propane Installation Code (CAN/
CGA B149.1) in Canada when installing this product.
Note: For water heater installations in Massachusetts,
refer to section “17. Requirements for State of
Massachusetts” on page 61.
1. Select an interior location for the installation. Each
installation is unique; therefore, take the time to find the
best location for the water heater.
a. Install the water heater near locations that use hot
water, such as bathroom, kitchen, or laundry room
faucets.
b. Select a location that minimizes the length of the
water pipe.
c. If the distances are long or if the faucet or appliance
requires “instant” hot water, we recommend running
a recirculation pipe back to the water heater from the
farthest fixture.
d. Insulate the hot water supply and recirculation pipes.
e. Select a location away from foot traffic and away from
areas where dust, debris, chemical agents, or other
combustible materials could accumulate.
f. Allow sufficient space for service and maintenance
access to all gas, water, and drain connections. Refer
to “3.3 Clearance Requirements” on page 9.
g. Make sure the location meets all building code
requirements.
2. Minimize the distance that the exhaust gas outlet and air
intake inlet must travel to an exterior wall.
a. The exhaust gas outlet must not be located next to a
walkway, near soffit vents, crawl space vents, or other
areas where condensate (water vapor) could cause
damage or create a hazard. Refer to “7.7 Venting
Clearance Specifications” on page 25 for additional
information.
b. The air intake inlet vent must be separated from the
exhaust gas outlet per guidelines in section “7. Air
Intake Inlet and Exhaust Gas Outlet Pipe Connections”
on page 18.
c. Contaminated or dirty air drawn into the intake pipe
can damage the water heater. The warranty does not
cover damage caused by airborne contaminants.
3. Locate the unit close to a drain and near gas and water
connections.
The water heater produces a significant amount of
condensate during normal operation and should be
located near a suitable drain where damage from a
possible leak will be minimal. Installing the water heater
in a location, without a drain, will void the warranty
and the manufacturer will not be responsible for any
resulting water damages that may occur. For additional
information, refer to”8.4 Condensate Drain Line” on page
29.
4. Locate the water heater and all the water pipes in an area
where the ambient temperature always remains above
freezing.
a. When the water heater is connected to an electrical
power supply, it will automatically prevent the water
from freezing inside the unit.
b. The unit’s freeze protection system will not prevent
the water in the surrounding pipes from freezing.
NOTICE
In cold climates, if there is a power failure, the unit’s freeze
protection system will not operate and can result in water
freezing inside the heat engine. To prevent damage to the
water heater, turn OFF the gas supply and inlet water valve.
Drain the unit completely as per “14.2 Draining the Water
Heater” on page 49. Damage caused by freezing water is
not covered by the warranty.
5. Select an appropriate location for the intake air inlet and
exhaust gas outlet pipes to exit the building, as shown in
“7.7 Venting Clearance Specifications” on page 25.
6. Check the water quality.
a. Proper operation of the water heater requires that
the water meets EPA quality standards. The table
in section “18. Warranty” on page 62 shows the
maximum contaminant levels allowed, based on the
EPA National Secondary Drinking Water Regulations
(40 CFR Part 143.3).
b. If contaminated water is suspected, discontinue use of
the water heater and contact an authorized technician
or licensed professional.
c. If the incoming water is known to have a high mineral
content or “hardness” (see “18. Warranty” on page
62), treatment is recommended upstream from the
water heater.

iQ251 Preparation Before Installation 12
May 2018 - Revision 01
4.2 Selecting an Outdoor Installation Site
Note: When installing the water heater, follow all local
building codes and the current edition of the National
Fuel Gas Code (ANSI Z223.1/NFPA 54) in the USA,
or National Gas and Propane Installation Code (CAN/
CGA B149.1) in Canada when installing this product.
Note: For water heater installations in Massachusetts,
refer to section “17. Requirements for State of
Massachusetts” on page 61.
1. Select a location for the installation. Each installation is
unique; therefore, take the time to find the best location
for the water heater.
a. Install the water heater near locations that use hot
water, such as bathroom, kitchen, or laundry room
faucets.
b. Select a location that minimizes the length of the
water pipe.
c. If the distances are long or if the faucet or appliance
requires “instant” hot water, we recommend running
a recirculation pipe back to the water heater from the
farthest fixture.
d. Insulate the hot and cold water supply and
recirculation pipes to prevent freezing or burns due to
hot surfaces.
e. Select a location away from foot traffic and away from
areas where dust, debris, chemical agents, or other
combustible materials could accumulate.
f. Allow sufficient space for service and maintenance
access to all gas, water, and drain connections. Refer
to “3.3 Clearance Requirements” on page 9.
g. Make sure the location meets all building code
requirements.
h. Contaminated or dirty air drawn into the intake pipe
can damage the water heater. The warranty does not
cover damage caused by airborne contaminants.
i. Ensure that the air intake is free (and remains free)
from grass clippings, wood chips, landscaping, and
other debris. The exhaust gas outlet must be above
the minimum code height of the defined snow line for
the surrounding area.
j. Install Intellihot outdoor kit IGT-SPR0063. For
installation instructions and details, see manual
IGT-MNL0019
2. Locate the unit close to a drain and near gas and water
connections.
The water heater produces a significant amount of
condensate during normal operation and should be located
near a suitable drain where damage from a possible leak
will be minimal. If installing on a roof, installing the water
heater in a location, without a drain, will void the warranty
and the manufacturer will not be responsible for any
resulting water damages that may occur. For additional
information, refer to “8.4 Condensate Drain Line” on page
29.
3. Locate the water heater and all the water pipes in an area
where they can be properly insulated.
a. When the water heater is connected to an electrical
power supply, it will automatically prevent the water
from freezing inside the unit.
b. The unit’s freeze protection system will not prevent
the water in surrounding pipes from freezing.
NOTICE
If there is a power failure, the unit’s freeze protection system
will not operate and can result in water freezing inside the
heat engine. To prevent damage to the water heater, turn
OFF the gas supply and inlet water valve. Completely drain
the unit as per “14.2 Draining the Water Heater” on page
49. Damage caused by freezing water is not covered by
the warranty.

13 iQ251 Wall Mounting
May 2018 - Revision 01
5. Wall Mounting
5.1 Mounting the Unit to the Wall
All water heaters come with an upper mounting bracket with
predrilled holes spaced on 16 inch centers to facilitate easy
installation on standard wall studs.
If the strength of the wall is insufficient or if the framing is
nonstandard or uneven, reinforce the area using a sheet of
plywood before installing the water heater.
Avoid installation on inside walls that can transmit operational
noises to occupants while the unit is operating.
To mount the water heater to the wall:
1. Place the upper mounting bracket on the wall and ensure
that it is level. Use two appropriately sized wood screws
to mount the bracket securely to the studs. Ensure that
it is affixed securely and can support the weight of the 90
pound unit.
SAFETY
INSTRUCTIONS
Only the brackets included with the water heater
should be used to mount the unit. Water heaters weigh
approximately 90 lbs. and must be securely attached to
the wall.
CAUTION
According to the National Institute for
Occupational Safety and Health, the
recommended maximum safe lifting weight is
51 lbs., with all lifting conditions perfect;
minimal forward reach, steady load close to the body,
straight back, load between knees and shoulders, and
good grips. To avoid personal injury, always use these
proper lifting techniques and use two people to move
the water heater, which weighs 90 lbs.
2. With assistance, hang the unit’s interlocking bracket (1)
onto wall bracket (2).
3. Loosen the four mounting screws in the lower bracket,
and slide it against the wall to create a 5/8” air space.
3
4. Retighten the four mounting screws and install two
appropriately sized wood screws in lower bracket (3) to
secure the unit to the wall.
5. Make sure the unit is plumb and level, and tighten the
four sheet metal screws on bottom bracket (3). When
properly installed, there should be a 5/8” air space
between the back of the water heater and the wall.

iQ251 Gas Connection 14
May 2018 - Revision 01
6. Gas Connection
WARNING
FIRE AND/OR EXPLOSION HAZARD
To avoid serious injury or even death, the gas pipe
installation and the gas pipe inlet pressure test must be
done by a licensed professional.
Always match the water heater with the type of gas
supplied to the unit (natural gas or propane). The water
heater is factory preset for natural gas.
Make sure the gas pipe pressures are within normal
limits. Pressures outside normal limits can result in
poor performance and hazardous operating conditions.
6.1 Quick Reference Installation Instructions
1. Determine fuel source; natural gas or propane, as shown
in “6.2 Fuel Source” on page 14.
2. Measure gas pressure, as shown in “6.3 Gas Pressure
Requirements” on page 14.
3. Install a gas pressure regulator and vent pipe if gas
pressure is above maximum recommendations, as shown
in “6.4 Gas Pressure Regulator” on page 14.
4. Measure the length of the supply pipe, as shown in “6.5
Length of Gas Supply Pipe” on page 14”.
5. Select the proper gas piping material, as shown in “6.5
Length of Gas Supply Pipe” on page 14.
6. Select the proper gas piping diameter, as shown in “6.7
Determine Correct Gas Pipe Diameter” on page 15.
7. Install a drip leg on the gas pipe, as shown in “6.8 Gas
Pipe Drip Leg and Shut-off Valve” on page 15.
8. Install a manual shut-off valve, as shown in “6.8 Gas Pipe
Drip Leg and Shut-off Valve” on page 15.
9. Test all gas pipe connections for leaks.
NOTICE
Do not fire (operate) the water heater until all connections
have been completed and the heat engine is filled with water.
6.2 Fuel Source
1. Natural gas is the factory preset.
2. To convert the unit to propane, refer to “11. Natural Gas
to Propane Conversion” on page 37.
6.3 Gas Pressure Requirements
iQ series water heaters are designed to operate at gas
pressures as low as 2.5” W.C. (at maximum firing rate). Gas
inlet pressures to the unit should not exceed 14” W.C. under
any condition (when unit is firing or not firing).
Natural Gas Static Gas Pressure
Parameters Specifications
Minimum Static Gas Pressure 1/2”
(black iron pipe) 6” W.C.
Minimum Static Gas Pressure 3/4”
(black iron pipe) 2.5” W.C.
Recommended Gas Pressure 8” W.C.
Maximum Static Gas Pressure 14” W.C.
6.4 Gas Pressure Regulator
1. If the gas inlet pressure is higher than recommended,
install a gas pressure regulator to lower gas pressure to
an acceptable level.
2. The gas pressure regulator must have the same or higher
minimum to maximum modulation range as the iQ model
it is regulating. For example, an iQ251 gas pressure
regulator should have a modulation range of 30,000
BTU/h to 251,000 BTU/h.
3. When multiple units are connected, use a dedicated gas
pressure regulator for each unit.
4. Regulators should be mounted with a minimum of 12” of
straight length pipe on either side.
6.4.1 Venting of Gas Supply Regulators
Make sure the gas supply regulator is properly vented by
following all local codes and the gas regulator manufacturer’s
recommendations.
1. The vent pipe must be at least the same size as the
regulator vent.
2. When multiple units are connected, each regulator must
have a separate vent pipe.
3. Vent pipes must not be connected together or connected
with any other appliance requiring external venting.
4. When selecting the size, the pipe diameter must be
increased by one size for every 20 feet of pipe.
a. Each 90° elbow is equivalent to approximately:
4.5 feet for nominal pipe sizes of up to 1-1/2”
10.5 feet for nominal pipe sizes of up to 4”.
b. Each 45° elbow is equivalent to approximately:
2 feet for nominal pipe sizes of up to 1-1/2”
5 feet for nominal pipe sizes of up to 4”.
6.5 Length of Gas Supply Pipe
1. Make sure the length of the supply pipe does not exceed
the maximum recommended length as per “6.9 Gas Pipe
Sizing Tables” on page 16.
a. Measure the straight length of the gas supply pipe
from the gas meter to the water heater or other
appliances requiring gas. Include the additional length
for any elbows into the calculation. The diameter of
the pipe must be in relation to the length.

15 iQ251 Gas Connection
May 2018 - Revision 01
b. The total straight length of gas pipe, as well as the
additional length for any elbows, must be considered
when sizing the gas pipe. Total equivalent length should
be calculated from the meter or source location to the
last connected water heater.
c. Gas pipe size should be selected on the total
equivalent length. The gas volume for cubic feet
per hour (CFH) flow will be the input divided by the
calorific value of the fuel to be supplied.
d. Use “6.9 Gas Pipe Sizing Tables” on page 16 or refer
to the gas pipe manufacturers sizing information to
determine the correct diameter for the supply pipe.
e. The diameter of the gas pipe will vary according to the
specific installation requirements.
6.6 Gas Piping Material
1. All gas pipe and components must comply with NFPA
local codes and utility requirements minimum. Only gas
approved fittings, valves, or pipe should be used.
2. Standard industry practice for gas pipe is Schedule 40
iron pipe and fittings. All high and low gas pressure piping
systems must comply with local utility and building codes.
3. Assembled pipe should be clean of all scale, debris, metal
particles, or foreign material.
4. The piping must be supported from the floor, ceiling, or
walls and not by the water heater itself.
6.7 Determine Correct Gas Pipe Diameter
Note: The water heater should be the first appliance to be
connected to the gas supply pipe.
1. Determine the gas requirement of the water heater(s)
and other appliances requiring gas.
2. Size the pipe diameter according to the COMBINED total
maximum BTUH volume for all the appliances as if they
were all operating at the same time. Use “6.9 Gas Pipe
Sizing Tables” on page 16.
3. Select the proper header pipe according to the number of
units being connected together, as shown in the chart.
Header Sizing for Multiple iQ Units
Number of
Heaters 1234
Sch 40 Iron
Pipe 2” 2” 3” 3”
4. The maximum pressure drop from the source to the final
water heater must not exceed 0.3” W.C.
5. The maximum gas flow rate required is the sum of
the maximum inputs of each unit divided by the heat
of combustion of the fuel supplied at the location,
(approximately 1,030 BTU per cubic foot for natural gas
or 2,520 BTU per cubic foot for propane).
Note: The fuel supplier or utility should be consulted to
confirm that sufficient volume and normal pressure is
provided to the building at the discharge side of the
gas meter or supply pipe.
6.8 Gas Pipe Drip Leg and Shut-off Valve
1. Install a shut-off valve. Local codes may require multiple
units to have a shut-off valve on the main gas supply pipe
and one on each unit.
2. Install a gas pipe drip leg on each water heater to prevent
dirt, condensation, or debris from entering the gas inlet.
a. Local codes may require multiple units to have a full
size drip leg on the main gas supply pipe and one on
each unit.
b. The drip leg should have a removable clean-out cap.
c. The gas pipe must not be supported by the water
heater or the drip leg.
3. If an excess flow valve (EFV) is installed in the gas pipe,
check the manufacturer’s minimum and maximum flow
capacity rating. An improperly sized EFV will not allow
the full flow of gas to the water heater and will cause the
unit to malfunction.
NOMINAL CLOSURE
FLOW RATE (SCFH): 335
MAXIMUM LOAD
CAPACITY (BTU/HR) 275,000
4. Continue installing pipe to reach the main gas supply
connection.
5. Test all gas pipe connections.
a. All the gas pipe connections should be tested as
prescribed in NFPA 54.
b. In multiple unit applications, each unit should be
isolated before testing any piping system that may
exceed the allowable pressure of 14.0” W.C.
NOTICE
Do not fire (operate) the water heater until all connections
have been completed and the heat engine is filled with water.

iQ251 Gas Connection 16
May 2018 - Revision 01
6.9 Gas Pipe Sizing Tables
This information is for reference only. Refer to gas pipe manufacturer specifications for actual delivery capacity. Contact the
local gas supplier for actual BTU/ft3rating. This data has been copied from the National Fire Protection Association Article 54
(NFPA 54).
Pipe Sizes and BTU/h Capacity (NATURAL GAS). Use this table for static gas pressure
LESS THAN 5” W.C.
Length
including
fittings (feet)
3⁄4" 1" 1-1/4" 1-1/2" 2" 2-1/2" 3" 4"
10 360,000 678,000 1,390,000 2,090,000 4,020,000 6,400,000 11,300,000 23,100,000
20 247,000 466,000 957,000 1,430,000 2,760,000 4,400,000 7,780,000 15,900,000
30 199,000 374,000 768,000 1,150,000 2,220,000 3,530,000 6,250,000 12,700,000
40 - 320,000 657,000 985,000 1,900,000 3,020,000 5,350,000 10,900,000
50 - 284,000 583,000 873,000 1,680,000 2,680,000 4,740,000 9,660,000
60 - 257,000 528,000 791,000 1,520,000 2,430,000 4,290,000 8,760,000
70 - 237,000 486,000 728,000 1,400,000 2,230,000 3,950,000 8,050,000
80 - 220,000 452,000 677,000 1,300,000 2,080,000 3,670,000 7,490,000
90 - 207,000 424,000 635,000 1,220,000 1,950,000 3,450,000 7,030,000
100 - - 400,000 600,000 1,160,000 1,840,000 3,260,000 6,640,000
125 - - 355,000 532,000 1,020,000 1,630,000 2,890,000 5,890,000
150 - - 322,000 482,000 928,000 1,480,000 2,610,000 5,330,000
175 - - 296,000 443,000 854,000 1,360,000 2,410,000 4,910,000
200 - - 275,000 412,000 794,000 1,270,000 2,240,000 4,560,000
Note: BTU/h capacities are based on specific gravity of 0.6, pressure drop of 0.5” W.C.
Pipe Sizes and BTU/h Capacity (NATURAL GAS). Use this table for static gas pressure
GREATER THAN 5” W.C.
Length
including
fittings (feet)
1/2" 3⁄4" 1" 1-1/4" 1-1/2" 2" 2-1/2" 3" 4"
10 404,000 949,000 1,787,000 3,669,000 5,497,000 10,588,000 16,875,000 29,832,000 43,678,000
20 286,000 652,000 1,228,000 2,522,000 3,778,000 7,277,000 11,598,000 20,503,000 30,020,000
30 233,000 524,000 986,000 2,025,000 3,034,000 5,844,000 9,314,000 16,465,000 24,107,000
40 202,000 448,000 844,000 1,733,000 2,597,000 5,001,000 7,971,000 14,092,000 20,632,000
50 - 397,000 748,000 1,536,000 2,302,000 4,433,000 7,065,000 12,489,000 18,286,000
60 - 360,000 678,000 1,392,000 2,085,000 4,016,000 6,401,000 11,316,000 16,569,000
70 - 331,000 624,000 1,280,000 1,919,000 3,695,000 5,889,000 10,411,000 15,243,000
80 - 308,000 580,000 1,191,000 1,785,000 3,437,000 5,479,000 9,685,000 14,181,000
90 - 289,000 544,000 1,118,000 1,675,000 3,225,000 5,140,000 9,087,000 13,305,000
100 - 273,000 514,000 1,056,000 1,582,000 3,046,000 4,856,000 8,584,000 12,568,000
125 - 242,000 456,000 936,000 1,402,000 2,700,000 4,303,000 7,608,000 11,139,000
150 - 219,000 413,000 848,000 1,270,000 2,446,000 3,899,000 6,893,000 10,093,000
175 - 202,000 380,000 780,000 1,169,000 2,251,000 3,587,000 6,342,000 9,285,000
200 - - 353,000 726,000 1,087,000 2,094,000 3,337,000 5,900,000 8,638,000
Note: For 1/2” pipe BTU/h capacities are based on specific gravity of 0.6, pressure drop of 4.6” W.C. For all other pipe sizes, capacities are based on
specific gravity of 0.6, pressure drop of 3.0” W.C.

17 iQ251 Gas Connection
May 2018 - Revision 01
Pipe sizes and BTU/h capacity (PROPANE). Use this table for static gas pressure
GREATER THAN 5” W.C.
Length
including
fittings (feet)
1/2" 3⁄4" 1" 1-1/4" 1-1/2" 2" 2-1/2" 3" 4"
10 409,000 608,000 1,150,000 2,350,000 3,520,000 6,790,000 10,800,000 19,100,000 39,000,000
20 289,000 418,000 787,000 1,620,000 2,420,000 4,660,000 7,430,000 13,100,000 26,800,000
30 236,000 336,000 632,000 1,300,000 1,940,000 3,750,000 5,970,000 10,600,000 21,500,000
40 204,000 287,000 541,000 1,110,000 1,660,000 3,210,000 5,110,000 9,030,000 18,400,000
50 - 255,000 480,000 985,000 1,480,000 2,840,000 4,530,000 8,000,000 16,300,000
60 - 231,000 434,000 892,000 1,340,000 2,570,000 4,100,000 7,250,000 14,800,000
80 - 212,000 400,000 821,000 1,230,000 2,370,000 3,770,000 6,670,000 13,600,000
100 - - 372,000 763,000 1,140,000 2,200,000 3,510,000 6,210,000 12,700,000
125 - - 349,000 716,000 1,070,000 2,070,000 3,290,000 5,820,000 11,900,000
150 - - 330,000 677,000 1,010,000 1,950,000 3,110,000 5,500,000 11,200,000
175 - - 292,000 600,000 899,000 1,730,000 2,760,000 4,880,000 9,950,000
200 - - 265,000 543,000 814,000 1,570,000 2,500,000 4,420,000 9,010,000
Note: The pipe BTU/h capacities are based on specific gravity of 1.5, pressure drop of 0.5” W.C.

iQ251 Air Intake Inlet and Exhaust Gas Outlet Pipe Connections 18
May 2018 - Revision 01
7. Air Intake Inlet and Exhaust Gas Outlet Pipe Connections
DANGER
Improper venting of the water heater
will result in excessive levels of carbon
monoxide, which can lead to severe
personal injury or death. This water
heater must be vented in accordance with the “Venting
of Equipment” section of the latest edition of the ANSI
Z223.1 / NFPA 54 (Natural Fuel Gas Code) in the USA,
or in Canada refer to the “Venting Systems and Air
Supply for Appliances” section in the latest version of
CAN/CGA B149.1 (Natural Gas and Propane Installation
Code), and all applicable local building codes. The
installation of the exhaust gas outlet pipe should be
performed only by a licensed professional.
WARNING
Do not operate flood damaged water heaters.
Install venting system according to the
required codes and material manufacturers
specifications.
Do not obstruct fresh air intakes or exhaust
outlets. Adequately support all vent system
piping.
Do not place vapor emitting products near
water heater or air intake.
Place working carbon monoxide detectors
outside each sleeping area.
Do not operate the water heater before
properly installing the exhaust outlet.
Visually inspect the vent system and
eliminate any possible area where
condensation could create a blockage of
intake or exhaust air.
Breathing concentrated levels of carbon
monoxide, even for a short period of time, will
cause brain damage and can even lead to
death.
BREATHING HAZARD
CARBON MONOXIDE GAS
•
•
•
•
•
•
•
Note: This water heater falls into the Category IV appliance.
7.1 Quick Reference Installation Guide
1. Select the desired type of venting system: Two Pipe Vent
System (Direct) or Single Pipe Vent System (Power).
“7.3 Two Pipe Vent System (Direct Vent)” on page 19.
“7.4 Single Pipe Venting System (Power Vent)” on page
21.
2. Select the desired termination of the air intake inlet and
exhaust gas outlet pipe; outside wall or roof.
“7.3.3 Side Wall Air Intake Inlet and Exhaust Gas Outlet
Pipe Termination” on page 20.
“7.3.4 Roof Air Intake Inlet and Exhaust Gas Outlet Pipe
Termination” on page 21.
3. Determine the straight pipe distance and the number of
elbows required to route the air intake inlet and exhaust
gas outlet pipes to their termination point.
“7.6 Intake Air Inlet and Exhaust Gas Outlet Pipe Diameter
and Length” on page 24.
4. Determine the diameter of pipe required to properly bring
in intake air and vent exhaust gas.
“7.6 Intake Air Inlet and Exhaust Gas Outlet Pipe Diameter
and Length” on page 24.
5. Verify the location of the air intake inlet and exhaust gas
outlet terminations are within state and local codes.
“7.7 Venting Clearance Specifications” on page 25.
6. Select an approved material for the air intake inlet pipe
as per “7.9 Air Intake Inlet Pipe Vent Materials” on page
26.
7. Select an approved material for the exhaust gas outlet
pipe as per “7.8 Exhaust Gas Outlet Pipe Materials” on
page 26.
7.2 Typical Single Unit Air Intake Inlet and
Exhaust Gas Outlet Pipe Installation
1. Select one of the two venting configurations: two pipes
(direct vent) configuration or with one pipe (power vent)
configuration.
2. Select the desired termination location and make sure
each pipe terminates within all local and state codes.
3. Select the desired material for the air intake inlet and
exhaust gas outlet pipes.
CAUTION
This water heater has a factory preset control
to limit the exhaust gas temperature to 149°F
(65°C) when PVC is selected in the “Flue
Type” programming section. As a result, the
water heater can be vented with Schedule 40 PVC. If
the incoming (or recirculation return) water temperature
does not exceed 150°F (66°C), the exhaust gas
temperature will not exceed 149°F (65°C).
WARNING
When the unit is set for CPVC (polypropylene pipe), flue
temperatures can reach 190°F (88°C). PVC pipe will
melt at temperatures above 149°F (65°C) and could,
therefore, result in a fire. Make sure the setting and the
type of material (“7.8 Exhaust Gas Outlet Pipe Materials”
on page 26) being used for the flue are compatible.
For this application use Schedule 80 CPVC or Approved
Polypropylene in the USA or Type BH Special Gas Vent
Class IIB (CPCV) or Class IC (Polypropylene) that
conforms to ULC-S636 in Canada. Also refer to “7.8
Exhaust Gas Outlet Pipe Materials” on page 26.

19 iQ251 Air Intake Inlet and Exhaust Gas Outlet Pipe Connections
May 2018 - Revision 01
SAFETY
INSTRUCTIONS
On multiple unit installations, the air intake inlet and
exhaust gas outlet pipe from each water heater must be
connected into the properly-sized common piping. Use
the table in “7.6 Intake Air Inlet and Exhaust Gas Outlet
Pipe Diameter and Length” on page 24 to determine
the diameter of the common connecting piping between
each individual water heater.
4. Determine the length and corresponding diameter for the
air inlet pipe and route the pipe to the desired termination
location.
a. For termination of the pipe to the outside, continue
installing the required pipe to a suitable outside
location. Glue all connections, making sure the joints
are sealed airtight.
b. Install suitable pipe support hangers every four to five
feet, or as local building codes require.
IH-39
5. Determine the length and corresponding diameter for the
exhaust gas outlet pipe and route it to a suitable outside
location.
a. Glue all connections, making sure the joints are sealed
airtight.
b. Install all horizontal exhaust gas outlet pipe with a
minimum two degree (1/4” per foot) slope back
toward the water heater. This allows any condensate
that accumulates in the exhaust gas outlet pipe to
properly drain back into the unit.
c. Install suitable pipe support hangers every four to five
feet, or as local building codes require.
SAFETY
INSTRUCTIONS
Do not connect any other appliance vents to the water
heater inlet or outlet pipes.
6. If multiple units are installed, make sure the diameter of
the connecting exhaust gas outlet pipe is properly sized
for the number of units being installed.
7.3 Two Pipe Vent System (Direct Vent)
7.3.1 Single Unit Configurations
The water heater can be directly vented without any
modification using a three inch diameter pipe.
The following diagrams represent some typical direct venting
configurations and are included to assist in designing the
vent system. Possible configurations are not limited to the
following diagrams.
Intake
Air
Exhaust
Intake
Air
Exhaust
Intake
Air
Exhaust

iQ251 Air Intake Inlet and Exhaust Gas Outlet Pipe Connections 20
May 2018 - Revision 01
7.3.2 Multiple Units Configurations
When more than one unit is installed, refer to “7.6 Intake Air
Inlet and Exhaust Gas Outlet Pipe Diameter and Length” on
page 24.
Connecting multiple units together requires proper sizing of
the air intake inlet and exhaust gas outlet pipes. Up to ten
water heaters can be connected (cascaded) together.
Units common vented must be cascaded together, refer to
"13. Connecting Multiple Units"
The following diagrams represent some typical direct venting
configurations and are included to assist in designing the
vent system. Possible configurations are not limited to the
following diagrams.
Intake
Air
Intake
Air
Intake
Air
Exhaust
Exhaust
Exhaust
7.3.3 Side Wall Air Intake Inlet and Exhaust Gas
Outlet Pipe Termination
1. Terminate the air intake inlet pipe with a 90° elbow
(angled down). Use a flange and PVC screen (not
supplied).
2. Terminate the exhaust gas outlet pipe on the exterior wall
at least 12” above ground and at least 18” away from the
air intake inlet pipe, or as required by local building codes.
In areas of high snow fall, protect the vent terminations
from blockage. Use a flange and PVC guard to seal the
opening against weather infiltration.
IQ-020
Intake Air
Exhaust
See Note A
Single unit.
IQ-020a
Exhaust
Intake Air
See
Note A
Multiple units.
Note A: The distance between any exhaust gas outlet and
air intake inlet pipe should be between 18 and 36
inches apart. If this minimum specification cannot
be met, the air intake inlet and exhaust gas outlet
pipes should be spaced 72 inches apart or farther.
3. To avoid moisture and frost build-up to openings on
adjacent homes, use 45° elbows, 90° elbows, or tees for
the exhaust gas outlet termination to direct the exhaust
gas fumes away from the building.