American Water Heater 40 Gallon 42000 BTU UltraLow Nox Power Vent Natural Gas Water Heater PVUG6240T42NV User Manual

							1
Power Vented
Ultra Low Nox
Gas Water Heater
All technical and warranty questions should be directed to the 
local dealer from whom the water heater was purchased. If you 
are unsuccessful, contact the company listed on the rating plate 
on the water heater.
When calling for assistance, please have the 
following information ready:
1. Model number
2. Product number
3. Serial number
4. Date of installation
5. Place of purchase
Table of Contents     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
322730-001 May 2013
Flammable Vapor Ignition Resistant Compliant
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.
  •  If you cannot reach your gas 
    supplier, call the fire department.
Installation and service must be performed 
by a qualified installer, service agency or 
the gas supplier.
WARNING:  If the information in these
instructions is not followed exactly, a fire 
or explosion may result causing property 
damage, personal injury or death.
INSTALLER:
•  AFFIX THESE INSTRUCTIONS TO OR ADJACENT   TO THE WATER HEATER.
OWNER:
•  RETAIN THESE INSTRUCTIONS AND WARRANTY  FOR FUTURE REFERENCE. RETAIN THE ORIGINAL 
RECEIPT AS PROOF OF PURCHASE.
Installation 
Instructions and 
Use & Care Guide
LOW LEAD CONTENT 
						

							2
Table Of Contents
Water Heater Safety   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . 2
Installing Your Gas Water Heater   . . . . . . . . . . . . . . . . . . . . . . . . . . .  3-17
  Unpacking the Water Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
  Location Requirements  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5-6
  Gas Supply  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . 7
  Combustion Air Supply/Vent Pipe System . . . . . . . . . . . . . . . . . .  8-12
  Outlet Terminations  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . 13
  Water System Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14-16
  Electrical Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
  Special Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . \
. 17
  Installation Checklist  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 18
Operating Your Water Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  19-21
  Lighting Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . \
. 19
  Operational Conditions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Maintenance of Your Water Heater  . . . . . . . . . . . . . . . . . . . . . . . . .  22-24     
Troubleshooting Charts  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25-27
Repair Parts Illustration  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  28-29PAGE
Important Instructions
•  Do not use this appliance if any part has been under water. Immediately call a qualified service technician. Water  heaters subjected to flood conditions or any time the gas controls, main\
 burner or pilot have been submerged in 
water require replacement of the entire water heater.
•  Hydrogen gas can be produced in a hot water system that has not been use\
d for a long period of time (generally  two weeks or more). Hydrogen gas is extremely flammable and can ignite \
when exposed to a spark or flame. To 
prevent the possibility of injury under these conditions, we recommend t\
he hot water faucet be opened for several 
minutes at the kitchen sink before using any electrical appliance which \
is connected to the hot water system. If 
hydrogen is present, there will probably be an unusual sound such as air\
 escaping through the faucet as water 
begins to flow. Do not smoke or have any open flame near the faucet at the time it is \
open.
The California Safe Drinking Water and Toxic Enforcement Act requires the Governor of California to publish a list of 
substances known to the State of California to cause cancer, birth defects, or other reproductive harm, and requires 
businesses to warn of potential exposure to such substances.
•  WARNING:  This product contains a chemical known to the State of California to cau\
se cancer, birth defects, or  other reproductive harm. 
•  This appliance can cause low-level exposure to some of the substances li\
sted in the Act.
This product is certified to comply with a maximum weighted average of 0\
.25% lead content as required in some areas.
WATER HEATER SAFETY
This is the safety alert symbol.  It is used to alert you 
to potential personal injury hazards.  Obey all safety 
messages that follow this symbol to avoid possible 
injury or death.
 DANGER 
 WARNING 
 CAUTION  
DANGER indicates an imminently 
hazardous situation which, if not avoided, 
will result in death or injury.
WARNING indicates a potentially hazardous 
situation which, if not avoided, could result 
in death or injury.
CAUTION  indicates a potentially hazardous 
situation which, if not avoided, could result 
in minor or moderate injury.
CAUTION used without the safety alert 
symbol indicates a potentially hazardous 
situation which, if not avoided, could result 
in property damage.
CAUTION 
						

							3
INSTALLING YOUR GAS WATER HEATER
Consumer Information
This water heater is design-certified by CSA International 
as a Category IV, non-direct vented water heater which 
takes its combustion air either from the installation area or 
from air ducted to the unit from the outside.
This water heater must be installed according to all local 
and state codes or, in the absence of local and state 
codes, the “National Fuel Gas Code”, ANSI Z223.1(NFPA 
54)-current edition. 
CSA America,  Inc.
8501 East Pleasant Valley Road
Cleveland, OH 44131
National Fire Protection Association
1 Batterymarch Park
Quincy, MA 02269
Check your phone listings for the local authorities 
having jurisdiction over your installation.
Consumer Responsibilities
This manual has been prepared to acquaint you with the 
installation, operation, and maintenance of your gas water 
heater and provide important safety information in these 
areas. 
Read all of the instructions thoroughly before attempting 
the installation or operation of this water heater. 
Do not discard this manual. You or future users of this 
water heater will need it for future reference.
Service to the power vented system should only be 
performed by a qualified person.
Examples of a qualified person include: licensed 
plumbers, authorized gas company personnel, and 
authorized service personnel.
If you lack the necessary skills required to properly install 
this water heater, or you have difficulty following the 
instructions, you should not proceed but have a qualified 
person perform the installation of this water heater. 
Massachusetts code requires this water heater to be 
installed in accordance with Massachusetts Plumbing and 
Fuel Gas Code 248 CMR Section 2.00 and 5.00.  See the 
following section in this manual: Installation Requirements 
for the Commonwealth of Massachusetts . 
A data plate identifying your water heater can be found 
next to the gas control valve/thermostat. When referring to 
your water heater, always have the information listed on 
the data plate readily available. 
Retain your original receipt as proof of purchase.
Unpacking the Water Heater
IMPORTANT: Do not remove any permanent instructions, 
labels, or the data label from either the outside of the water 
heater or on the inside of water heater panels.
•  Remove exterior packaging and place installation com- ponents aside.
•  Inspect all parts for damage prior to installation and  start-up.
•  Completely read all instructions before attempting to  assemble and install this product.
•  After installation, dispose of/recycle all packaging  materials.
WARNING
Excessive Weight Hazard
Use two or more people to move and install 
water heater.
Failure to do can result in back or 
other injury. 
						

							4
For all side wall terminated, horizontally vented power vent, direct ven\
t, and power direct vent gas fueled water heaters installed 
in every dwelling, building or structure used in whole or in part for re\
sidential purposes, including those owned or operated b y 
the Commonwealth and where the side wall exhaust vent termination is les\
s than seven (7) feet above  ¿ nished grade in the 
area of the venting, including but not limited to decks and porches, the\
 following requirements shall be satis ¿ ed: 
INSTALLATION OF CARBON MONOXIDE DETECTORS   At the time of installation of the side wall horizontal vented gas 
fueled equipment, the installing plumber or gas ¿ tter shall observe that a hard wired carbon monoxide detector with an al\
arm 
and battery back-up is installed on the  À oor level where the gas equipment is to be installed. In addition, the i\
nstalling plumber 
or gas ¿ tter shall observe that a battery operated or hard wired carbon monoxide\
 detector with an alarm is installed on each 
additional level of the dwelling, building or structure served by the si\
dewall horizontal vented gas fueled equipment. It shall  
be the responsibility of the property owner to secure the services of qu\
ali ¿ ed licensed professionals for the installation of hard 
wired carbon monoxide detectors.
In the event that the side wall horizontally vented gas fueled equipment\
 is installed in a crawl space or an attic, the hard wi red 
carbon monoxide detector with alarm and battery back-up may be installed\
 on the next adjacent  À oor level.
In the event that the requirements of this subdivision can not be met at\
 the time of completion of installation, the owner shal l 
have a period of thirty (30) days to comply with the above requirement\
s provided that during said thirty (30) day period, a bat -
tery operated carbon monoxide detector with an alarm shall be installed.\
APPROVED CARBON MONOXIDE DETECTORS   Each carbon monoxide detector as required in accordance with the above\
 
provisions shall comply with NFPA 720 and be ANSI/UL 2034 listed and CSA certi ¿ ed. 
SIGNAGE  A metal or plastic identi ¿ cation plate shall be permanently mounted to the exterior of the buildin\
g at a minimum height 
of eight (8) feet above grade directly in line with the exhaust vent t\
erminal for the horizontally vented gas fueled heating ap pli-
ance or equipment. The sign shall read, in print size no less than one-half (1/2) inch in\
 size,  “GAS VENT DIRECTLY BELOW. 
KEEP CLEAR OF ALL OBSTRUCTIONS.”
INSPECTION   The state or local gas inspector of the side wall horizontally vented ga\
s fueled equipment shall not approve the 
installation unless, upon inspection, the inspector observes carbon mono\
xide detectors and signage installed in accordance 
with the provisions of 248 CMR 5.08(2)(a) 1 through 4. 
EXEMPTIONS: The following equipment is exempt from 248 CMR 5.08(2)(a)1 through 4\
: 
1. The equipment listed in Chapter 10 entitled “Equipment Not Required To Be Vented” in the most current edition of NFPA 54 
as adopted by the Board; and 
2. Product Approved side wall horizontally vented gas fueled equipment installed in\
 a room or structure separate from the 
dwelling, building, or structure used in whole or in part for residentia\
l purposes. 
MANUFACTURER REQUIREMENTS - GAS EQUIPMENT VENTING SYSTEM PROVIDED  When the manufacturer of Product 
 Approved side wall horizontally vented gas equipment provides a venting \
system design or venting system components with 
the equipment, the instructions provided by the manufacturer for install\
ation of the equipment and the venting system shall 
include:
1. Detailed instructions for the installation of the venting system desi\
gn or the venting system components; and
2. A complete parts list for the venting system design or venting system. 
MANUFACTURER REQUIREMENTS - GAS EQUIPMENT VENTING SYSTEM NOT PROVIDED   When the manufacturer of 
a Product Approved side wall horizontally vented gas fueled equipment does not pro\
vide the parts for venting the  À ue gases, 
but identi ¿ es “special venting systems,” the following requirements shall be \
satis ¿ ed by the manufacturer:
1. The referenced “special venting system” instructions shall be incl\
uded with the appliance or equipment installation
 instructions; and 
2. The “special venting systems” shall be Product Approved by the Board, and the instructions for that system shall includ\
e a 
parts list and detailed installation instructions. 
A copy of all installation instructions for all Product Approved side wall horizontally vented gas fueled equipment, all ventin g 
instructions, all parts lists for venting instructions, and/or all venti\
ng design instructions shall remain with the appliance  or 
equipment at the completion of the installation. 
INSTALLATION REQUIREMENTS FOR THE COMMONWEALTH OF MASSACHUSETTS 
						

							5
FIRE AND EXPLOSION HAZARD
Can result in serious injury or death
        Do not store or use gasoline or other 
flammable vapors and liquids in the 
vicinity of this or any other appliance. 
Storage of or use of gasoline or other 
flammable vapors or liquids in the vicinity 
of this or any other appliance can result in 
serious injury or death.
Fl ammable VaporsFLAMMABLES
Read and follow water heater warnings and 
instructions.
WARNING
Do not use or store flammable products such as gasoline, 
solvents, or adhesives in the same room or area near the 
water heater. If such flammables must be used, all gas 
burning appliances in the vicinity must be shut off and their 
pilot lights extinguished. Open the doors and windows for 
ventilation while flammable substances are in use. 
If flammable liquids or vapors have spilled or leaked in 
the area of the water heater, leave the area immediately 
and call the fire department from a neighbor’s home. Do 
not attempt to clean the spill until all ignition sources have 
been extinguished.
WARNING
 
Fire or Explosion Hazard
Read instruction manual before installing, 
using or servicing water heater.
Improper use may result in fire or explosion.
Maintain required clearances to combustibles.
Keep combustibles such as boxes, magazines, clothes, 
etc. away from the water heater area. 
Site Location
•  Select a location near the center of the water piping   system. The water heater must be installed indoors  
and in a vertical position on a level surface. 
•  Consider the exhaust vent system piping  and combus- tion air supply requirements when selecting the water 
heater location. The venting system must be able to 
run from the water heater to the termination with a 
minimal length and number of elbows. The venting 
system must comply with the requirements set forth in 
the venting section of this manual.  
•  Locate the water heater near the existing gas  piping. If installing a new gas line, locate the water  
heater to minimize the pipe length and elbows. 
NOTE:  This water heater must be installed according to all 
local and state codes or, in the absence of local and state 
codes, the “National Fuel Gas Code”, ANSI Z223.1(NFPA 
54)-current edition. 
Location Requirements
Carbon Monoxide Poisoning Hazard
Do not install in a mobile home.
Doing so can result in death or 
carbon monoxide poisoning.
WARNING
IMPORTANT: Do not install the water heater or venting system 
in a location that will exceed 140°F ambient temperature.
The FVIR System is designed to reduce the risk of 
flammable vapor-related fires. Flammable liquids (such as 
gasoline, solvents, propane, etc,) emit flammable vapors 
which can be ignited by a gas water heater’s hot surface 
igniter or main burner. The resulting flashback and fire can 
cause death or serious burns to anyone in the area.
This heater is equipped with an FV sensor for detecting 
the presence of flammable vapors (Figure 1A). When 
the sensor detects those vapors, the unit will shut down 
and not operate.  Should this happen, please refer to the 
troubleshooting guide.  Even though this water heater is 
a flammable vapors ignition resistant water heater and 
is designed to reduce the chances of flammable vapors 
being ignited, gasoline and other flammable substances 
should never be stored or used in the same vicinity or area 
containing a gas water heater or other open flame or spark 
producing appliance.
FV Sensor
Figure 1A:
FV Sensor 
						

							6
•  The water heater should be located in an area not  
  subject to freezing temperatures. Water heaters 
  located in unconditioned spaces (i.e., attics, 
  basements, etc.) may require insulation of the    
  water piping and drain piping to protect against    
  freezing. The drain and controls must be easily    
  accessible for operation and service. Maintain    
  proper clearances as specified on the data plate.
•  Do not locate the water heater near an air-moving device. The operation of air-moving devices such as 
exhaust fans, ventilation systems, clothes dryers, 
fireplaces, etc., can affect the proper operation of 
the water heater. Special attention must be given to 
conditions these devices may create. Flow reversal 
of flue gases may cause an increase of carbon 
monoxide inside of the dwelling.  
Clearances and Accessibility
NOTE: Minimum clearances from combustible surfaces are 
stated on the data plate adjacent to the gas control valve/
thermostat of the water heater.
The water heater is certified for installation on a               
combustible floor. 
•  IMPORTANT: If installing over carpeting, the carpeting 
must be protected by a metal or wood panel beneath 
the water heater. The protective panel must extend 
beyond the full width and depth of the water heater 
by at least 3 inches (76.2mm) in any direction or if in 
a alcove or closet installation, the entire floor must be 
covered by the panel. 
WARNING
 
Fire Hazard
For continued protection 
against the risk of fire: 
Do not install water heater 
on carpeted floor.
Do not operate water heater 
if flood damaged.
•  Figure 1C may be used as a reference guide to locate  the specific clearance locations. A minimum of 24 
inches of front clearance and 4 inches on each side 
should be provided for inspection and service.
State of California
NOTE:  For California installation, this water heater must 
be braced, anchored, or strapped to avoid falling or moving 
during an earthquake. Correct installation procedure 
instructions may be obtained from California’s Office of the 
State Architect, 1102 Q street, Suite 5100, Sacramento, 
CA 95811. Instructions can also be downloaded to your 
computer at www.dsa.dgs.ca.gov/Pubs.
CAUTION - PROPERTY DAMAGE HAZARD
The water heater should be located in an area where 
leakage of the tank or connections will not result in 
damage to the area adjacent to the water heater or 
to lower floors of the structure. Due to the normal 
corrosive action of the water, the tank will eventually 
leak after an extended period of time. Also any 
external plumbing leak, including those from improper 
installation, may cause early failure of the tank due 
to corrosion if not repaired.  If the owner/operator 
is uncomfortable with making the repair, a qualified 
person should be contacted.  A suitable metal drain 
pan should be installed under the water heater as 
shown below to help protect the property from damage 
which may occur from condensate formation or leaks 
in the piping connections or tank. The pan must limit 
the water level to a maximum depth of 1-3/4” and 
be two inches wider than the heater and piped to an 
adequate drain. NOTE: The pan must not restrict 
combustion air flow.  Locate the water heater near a 
suitable indoor drain. Outside drains are subject to 
freezing temperatures which can obstruct the drain 
line. The piping should be at least 3/4” ID and pitched 
for proper drainage. 
1-3/4” max.
At least 2” greater 
than the water heater and the inlet air pipe. Pipe to an
adequate drain
Metal 
Drain 
Pan
FIGURE 1B FIGURE 1C
Minimum Clearance 
Locations
Front
24” min.
for service
Sides
Top to 
ceiling
Vent
Sides
Back
Top View 
						

							7
Gas Requirements
Read the data plate to be sure the water heater is made 
for the type of gas you will be using in your home. This 
information will be found on the data plate located near the 
gas control valve/thermostat. If the information does not 
agree with the type of gas available, do not install or light. 
Call your dealer.
NOTE:  An odorant is added by the gas supplier to the gas 
used by this water heater. This odorant may fade over an 
extended period of time. Do not depend upon this odorant 
as an indication of leaking gas.
Gas Piping
The gas piping must be installed according to all local and 
state codes or, in the absence of local and state codes, the 
“National Fuel Gas Code”, ANSI Z223.1(NFPA 54)-current 
edition.  
Table 1 on the following page provides a sizing reference 
for commonly used gas pipe materials. Consult the 
“National Fuel Gas Code” for the recommended gas pipe 
size of other materials.
Refer to Figure 2
NOTE:  When installing gas piping, apply approved pipe 
joint compound.
1.  Install a readily accessible manual shut-off valve in  the gas supply line as recommended by the local utility. 
Know the location of this valve and how to turn off the 
gas to this unit.
2.  Install a sediment trap (if not already incorporated as part  of the water heater) as shown. The sediment trap must 
be no less than three inches long for the accumulation of 
dirt, foreign material, and water droplets.
3.  Install a ground joint union between the gas control  valve/thermostat and the manual shut-off valve. This is to 
allow easy removal of the gas control valve/thermostat.
4.  Turn the gas supply on and check for leaks. Test all  connections by brushing on an approved noncorrosive 
leak-detection solution. Bubbles will show a leak. Correct 
any leak found.
Gas Pressure
IMPORTANT: The gas supply pressure must not exceed 
the maximum supply pressure as stated on the water 
heater’s data plate. The minimum supply pressure is for 
the purpose of input adjustment.
Gas Pressure Testing
IMPORTANT: This water heater and its gas connection 
must be leak tested before placing the appliance in 
operation.
•  If the code requires the gas lines to be tested at a    
  pressure exceeding 14” W.C., the water heater and   
  its manual shut-off valve must be disconnected from  
  the gas supply piping system and the line capped.
•  If the gas lines are to be tested at a pressure less    
  than 14” W.C., the water heater must be isolated    
  from the gas supply piping system by closing its    
  manual shut-off valve.
U.L. recognized fuel gas and carbon monoxide (CO) 
detectors are recommended in all applications and should 
be installed using the manufacturer’s instructions and local 
codes, rules, or regulations.
NOTE: Air may be present in the gas lines and could 
prevent the burner from lighting on initial start-up. The gas 
lines should be purged of air by a qualified person after 
installation of the gas piping system.
Explosion Hazard
Use a new CSA approved gas supply line.
Install a shut-off valve.
Do not connect a natural gas water heater to 
an L.P. gas supply.
Do not connect an L.P. gas water heater to a 
natural gas supply.
Failure to follow these instructions can 
result in death, explosion, or 
carbon monoxide poisoning.
WARNING
Gas SupplyFigure 2    
Gas Piping 
Manual gas
shut-off valve
Install a readily acces-
sible manual shut-off  valve in the gas supply 
line as recommended  by the local utility.
Sediment Trap 
						

							8
Combustion Air Supply
This water heater takes its combustion air either from the 
installation area or from air ducted to the unit from the 
outside and all combustion products are discharged to the 
outdoors.  
IMPORTANT:  Air for combustion and ventilation must not 
come from a corrosive atmosphere. Any failure due to 
corrosive elements in the atmosphere is excluded from 
warranty coverage.The following types of installation (not limited to the 
following) will require outdoor air for combustion due to 
chemical exposure and may reduce but not eliminate the 
presence of corrosive chemicals in the air:
• beauty shops
•  photo processing labs
•  buildings with indoor pools
•  water heaters installed in laundry, hobby, or craft rooms
•  water heaters installed near chemical storage areas
Combustion air must be free of acid-forming chemicals 
such as sulfur, fluorine, and chlorine. These elements are 
found in aerosol sprays, detergents, bleaches, cleaning 
solvents, air fresheners, paint, and varnish removers, 
refrigerants, and many other commercial and household 
products. When burned, vapors from these products form 
highly corrosive acid compounds. These products should 
not be stored or used near the water heater or air inlet.
Combustion and ventilation air requirements are 
determined by the location of the water heater. The water 
heater may be located in either an open (unconfined) area 
or in a confined area or small enclosure such as a closet 
or small room. Confined spaces are areas with less than 
50 cubic feet for each 1,000 BTUH of the total input for all 
gas-using appliances.
Combustion Air Supply and 
Ventilation
Carbon Monoxide Warning
Follow all the local and state codes or, in 
the absence of local and state codes, the 
“National Fuel Gas Code”, ANSI Z223.1 
(NFPA 
vent system.
Failure to do so can result in death, 
explosion, or carbon monoxide poisoning.
WARNING
54)- current edition to properly install 
						

							9
All Air from Outdoors
Outdoor fresh air can be provided to a confined area either 
directly or by the use of vertical and horizontal ducts. The 
fresh air can be taken from the outdoors or from crawl or 
attic spaces that freely communicate with the outdoors. 
Attic or crawl spaces cannot be closed and must be 
properly ventilated to the outside. 
Ductwork must be of the same cross-sectional area as 
the free area of the opening to which they connect. The 
minimum dimension of rectangular air ducts cannot be less 
than three inches. 
Unconfined Space
A water heater in an unconfined space uses indoor air for 
combustion and requires at least 50 cubic feet for each 
1,000 BTUH of the total input for all gas appliances. The 
table below shows a few examples of the minimum square 
footage (area) required for various BTUH inputs.
IMPORTANT: 
•  The area must be open and be able to provide the proper air requirements to the water heater. Areas that 
are being used for storage or contain large objects may 
not be suitable for water heater installation. 
•  Water heaters installed in open spaces in buildings with  unusually tight construction may still require outdoor air 
to function properly. In this situation, outside air open-
ings should be sized the same as for a confined space. 
•  Modern home construction usually requires supplying 
outside air into the water heater area. 
Confined Space 
For the correct and proper operation of this water heater, 
ample air must be supplied for the combustion, ventilation, 
and dilution of flue gases. Small enclosures and confined 
areas must have two permanent openings so that sufficient 
fresh air can be drawn from outside of the enclosure. One 
opening shall be within 12 inches of the top and one within 12 
inches of the bottom of the enclosure as shown in Figure 3.
The size of each opening (free area) is determined by the 
total BTUH input of all gas utilization equipment (i.e., water 
heaters, furnaces, clothes dryers, etc.) and the method by 
which the air is provided. The BTUH input can be found on 
the water heater data plate. Additional air can be provided 
by two methods:
  1.    All air from inside the building.
  2.    All air from outdoors.
Table 2
BTUHInput Min. Sq. Feet 
with 8’ Ceiling Typical Room
with 8’ Ceiling
30,000 1889 x 21
45,000 28114 x 20
60,000 37515 x 25
75,000 46915 x 31
90,000 56320 x 28
105,000 65720 x 33
120,000 75025 x 30
135,000 84428 x 30
All Air from Inside the Building
When additional air is to be provided to the confined area 
from additional room(s) within the building, the total volume 
of the room(s) must be of sufficient size to properly provide 
the necessary amount of fresh air to the water heater 
and other gas utilization equipment in the area. If you are 
unsure that the structure meets this requirement, contact 
your local gas utility company or other qualified agency for 
a safety inspection. 
Each of the two openings shall have a minimum free area 
of 1 square inch per 1,000 BTUH of the total input rating of 
all gas utilization equipment in the confined area, but not 
less than 100 square inches (Figure 4).
Figure 3 
Opening Locations 
Confined Spaces 
12” Max. 
Permanent 
openings to  
the outside or 
additional  
rooms within  
the building  Closet 
or other 
confined  space 
12” Max. 
     
  
Figure 4 
All Air From Inside Building 
Confined Space Installation 
Confined 
Space 
Permanent 
Openings 
1 Square  
inch/1000 
BTUH 
(min. 100 
sq. in.)  
						

							10 The size of each of the two openings is determined by the 
method in which the air is to be provided. Refer to Table 
3 to calculate the minimum free area for each opening. 
Figures 5, 6, and 7 are typical examples of each method. 
Louvers and Grilles
In calculating free area for ventilation and combustion 
air supply openings, consideration must be given to the 
blocking effect of protection louvers, grilles, and screens. 
These devices can reduce airflow, which in turn may 
require larger openings to achieve the required minimum 
free area. Screens must not be smaller than 1/4” mesh. If 
the free area through a particular design of louver or grille 
is known, it should be used in calculating the specified 
free area of the opening. If the design and free area are 
not known, it can be assumed that most wood louvers will 
allow 20 - 25% of free area while metal louvers and grilles 
will allow 60 - 75% of free area. 
Louvers and grilles must be locked open or interconnected 
with the equipment so that they are opened automatically 
during equipment operation. 
Keep louvers and grilles clean and free of debris or other 
obstructions.
Table 3Minimum Free Area of Permanent Openings for  Ventilation and Combustion Air Supply - 
All Air from Outdoors Only
Based on the total BTUH input rating for all gas utilizing equipment 
within the confined space.
Opening Source Minimum Free 
Area Per Opening  (Sq. In.) Reference 
Drawing
Directed to Outdoors* 1  sq. in. per 4000 BTUH Figure 5
Vertical Ducts 1  sq. in. per 4000 BTUH Figure 6
Horizontal Ducts 1  sq. in. per 2000 BTUH Figure 7
Single Opening 1  sq. in. per 3000 BTUH Figure 7A
Example: A water heater with an input rating of 50,000 BTUH using 
horizontal ducts would require each opening to have a minimum free 
area of 25 square inches.
Minimum free area = 50,000 BTUH x 1 sq. in. / 2000 BTUH = 25 sq. in.
*These openings connect directly with the outdoors 
through a ventilated attic, a ventilated crawl space, or 
through an outside wall.
Consult the local codes of your area for specific ventilation 
and combustion air requirements.
Figure 5
All Air From Outdoors: Inlet Air
From Ventilated Crawl Space/
Outlet Air to Vented Attic Gable Vent
to Outdoors
Install Above
Insulation
Confined Space
Outlet Air
to the Attic
1 sq. in. per
4000 BTUH
Inlet Air
from the
Crawl Space
Alternative
Air Inlet
1 sq. in. per
4000 BTUH Open
Foundation
Vent
Gable Vent
to Outdoors
Install Above
Insulation
Confined Space
Figure 6
All Air from Outdoors
Through Ventilated Attic
Outlet Air
to the Attic
1 sq. in. per
4000 BTUH
Inlet Air Duct
1 sq. in. per
4000 BTUH
12” Max.
Figure 7
All Air From Outdoors
Using Horizontal Ducts
ConfinedSpace
1 sq. in. per
2000 BTUH
Outlet
Outdoor
Air Ducts
Inlet 1 sq. in. per
2000 BTUH
Figure 7A
All Air From Outdoors
Using a Single 
Permanent Opening  
 
 
Confined
Space
1 sq. in. per
3000 BTUH
Alternative 
Opening 
Location