A. O. Smith GPVH-40 Installation Manual
Instruction Manual
RESIDENTIAL GAS WATER HEATERS
POWER VENTED GAS MODELS WITH HOT SURFACE IGNITION
NOT FOR USE IN MANUFACTURED (MOBILE) HOMES
GAMA certification applies
to all residential gas water
heaters with capacities of 20
to 100 gallons with input rating
of 75,000 BTU/Hr. or less.
• For Your Safety •
AN ODORANT IS ADDED TO THE GAS USED
BY THIS 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, PLEASE WRITE TO THE COMPANY LISTED ON THE RATING PLATE ON THE WATER HEATER.
KEEP THIS MANUAL IN THE POCKET ON HEATER FOR FUTURE REFERENCE
PRINTED 1208 315465-000
WHENEVER MAINTENANCE ADJUSTMENT OR SERVICE IS REQUIRED.
1
SAFE INSTALLATION, USE AND SERVICE
Your safety and the safety of others is extremely important in the installation, use and servicing of this water heater.
Many safety-related messages and instructions have been provided in this manual and on your own water heater to warn you and
others of a potential injury hazard. Read and obey all safety messages and instructions throughout this manual. It is very important
that the meaning of each safety message is understood by you and others who install, use or service this water heater.
All safety messages will generally tell you about the type of hazard, what can happen if you do not follow the safety message and
how to avoid the risk of injury.
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 cause cancer, birth defects, or other reproductive
harm. This appliance can cause low-level exposure to some of the substances included in the Act.
IMPORTANT DEFINITIONS
• Qualifi ed Installer: A qualifi ed installer must have ability equivalent to a licensed tradesman in the fi elds of plumbing,
air supply, venting and gas supply, including a thorough understanding of the requirements of the National Fuel Gas
Code as it relates to the installation of gas fi red water heaters. The qualifi ed installer must also be familiar with the
design features and use of fl ammable vapor ignition resistant water heaters, and have a thorough understanding of this
instruction manual.
• Service Agency: A service agency also must have ability equivalent to a licensed tradesman in the fi elds of plumbing,
air supply, venting and gas supply, including a thorough understanding of the requirements of the National Fuel Gas
Code as it relates to the installation of gas fi red water heaters. The service agency must also have a thorough
understanding of this instruction manual, and be able to perform repairs strictly in accordance with the service guidelines
provided by the manufacturer.
• Gas Supplier: The Natural Gas or Propane Utility or service who supplies gas for utilization by the gas burning
appliances within this application. The gas supplier typically has responsibility for the inspection and code approval of
gas piping up to and including the Natural Gas meter or Propane storage tank of a building. Many gas suppliers also
offer service and inspection of appliances within the building.
2
GENERAL SAFETY
3
TABLE OF CONTENTS
SAFE INSTALLATION, USE AND SERVICE............................2
GENERAL SAFETY..................................................................3
TABLE OF CONTENTS ............................................................4
INTRODUCTION ......................................................................4
Preparing for the New Installation .....................................4
INSTALLATION REQUIREMENTS FOR THE
COMMONWEALTH OF MASSACHUSETTS ...........................5
TYPICAL INSTALLATION ..................................................... 6-7
LOCATING THE NEW WATER HEATER ............................. 8-9
Facts to Consider About Location ................................. 8-9
Insulation Blankets ............................................................9
Combustion Air and Ventilation for Appliances
Located in Unconfi ned Spaces .........................................9
Combustion Air and Ventilation for Appliances
Located in Confi ned Spaces ....................................... 9-10
INSTALLING THE WATER HEATER ................................ 10-21
Water Piping ..............................................................11-12
Temperature-Pressure Relief Valve ................................12
Gas Piping ......................................................................13
Sediment Traps ...............................................................14
Blower Assembly Installation ..........................................14
Vent Pipe Connection to Blower Assembly .....................15
Venting and Installation ............................................. 15-16
LIGHTING & OPERATING LABEL .........................................21
TEMPERATURE REGULATION ............................................22
FOR YOUR INFORMATION ...................................................23
Start Up Conditions .........................................................23
Condensate.....................................................................23
Smoke/Odor ....................................................................23
Thermal Expansion .........................................................23
Strange Sounds ..............................................................23
Operational Conditions ...................................................23
Smelly Water ...................................................................23
“Air” in Hot Water Faucets ..............................................23
High Temperature Shut Off System ................................23
PERIODIC MAINTENANCE ...................................................24
Venting System Inspection..............................................24
Burner Inspection ............................................................24
Burner Cleaning ..............................................................24
Housekeeping ........................................................... 24-25
Anode Rod Inspection.....................................................25
Temperature-Pressure Relief Valve Operation ...............25
Draining...........................................................................25
Drain Valve Washer Replacement ............................ 25-26
Service ............................................................................26
LEAKAGE CHECKPOINTS ....................................................26
REPAIR PARTS ......................................................................27
TROUBLESHOOTING ..................................................... 28-30
WARRANTY ...........................................................................31
INTRODUCTION
Thank You for purchasing this water heater. Properly installed and
maintained, it should give you years of trouble free service.
Abbreviations Found In This Instruction Manual:
• CSA - Canadian Standards Association
• ANSI - American National Standards Institute
• NFPA - National Fire Protection Association
• ASME - American Society of Mechanical Engineers
• GAMA - Gas Appliance Manufacturer’s Association
• UL - Underwriters Laboratories Inc.
This gas-fi red water heater is design certifi ed by Underwriters Laboratories
Inc. under American National Standard/CSA Standard for Gas Water
Heaters ANSI Z21.10.1 • CSA 4.1 (current edition).
PREPARING FOR THE INSTALLATION
1. Read the “General Safety” section, page 3 of this manual fi rst and
then the entire manual carefully. If you don’t follow the safety rules,
the water heater will not operate properly. It could cause DEATH,
SERIOUS BODILY INJURY AND/OR PROPERTY DAMAGE.
This manual contains instructions for the installation, operation,
and maintenance of the gas-fi red water heater. It also contains
warnings throughout the manual that you must read and be aware
of. All warnings and all instructions are essential to the proper
operation of the water heater and your safety. Since we cannot put
everything on the fi rst few pages, READ THE ENTIRE MANUAL
BEFORE ATTEMPTING TO INSTALL OR OPERATE THE WATER
HEATER.
2. The installation must conform with these instructions and the local code
authority having jurisdiction. In the absence of local codes, installations
shall comply with the National Fuel Gas Code ANSI Z223.1/NFPA
54 and the National Electrical Code, NFPA 70. These publications
are available from The National Fire Protection Association, 1
Batterymarch Park, Quincy, MA 02269.
3. The water heater when installed must be grounded in accordance
with the local codes, or in the absence of local codes: In the United
States, the National Electrical Code. ANSI/NFPA 70.
4. If after reading this manual you have any questions or do not
understand any portion of the instructions, call the local gas utility or
the manufacturer whose name appears on the rating plate.
5. Carefully plan the place where you are going to put the water heater.
Correct combustion, vent action, and vent pipe installation are
very important in preventing death from possible carbon monoxide
poisoning and fi res, see Figures 1 and 2.
Examine the location to ensure the water heater complies with the
“Locating the New Water Heater” section in this manual.
6. For California installation this water heater must be braced, anchored,
or strapped to avoid falling or moving during an earthquake. See
instructions for correct installation procedures. Instructions may be
obtained from California Offi ce of the State Architect, 400 P Street,
Sacramento, CA 95814.
7. Massachusetts Code requires this water heater to be installed in
accordance with Massachusetts 248-CMR 2.00: State Plumbing Code
and 248-CMR 5.00. For more information see next page.
8. Complies with SCAQMD rule #1121 and districts having equivalent
NOx requirements.
4
INSTALLATION REQUIREMENTS FOR THE COMMONWEALTH OF MASSACHUSETTS
For all side wall terminated, horizontally vented power vent, direct vent, and power direct vent gas fueled water heaters installed
in every dwelling, building or structure used in whole or in part for residential purposes, including those owned or operated by
the Commonwealth and where the side wall exhaust vent termination is less than seven (7) feet above fi nished grade in the
area of the venting, including but not limited to decks and porches, the following requirements shall be satisfi ed:
INSTALLATION OF CARBON MONOXIDE DETECTORS At the time of installation of the side wall horizontal vented gas
fueled equipment, the installing plumber or gasfi tter shall observe that a hard wired carbon monoxide detector with an alarm
and battery back-up is installed on the fl oor level where the gas equipment is to be installed. In addition, the installing plumber
or gasfi 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 sidewall horizontal vented gas fueled equipment. It shall
be the responsibility of the property owner to secure the services of qualifi 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 wired
carbon monoxide detector with alarm and battery back-up may be installed on the next adjacent fl oor level.
In the event that the requirements of this subdivision can not be met at the time of completion of installation, the owner shall
have a period of thirty (30) days to comply with the above requirements provided that during said thirty (30) day period, a battery 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 certifi ed.
SIGNAGE A metal or plastic identifi cation plate shall be permanently mounted to the exterior of the building at a minimum height
of eight (8) feet above grade directly in line with the exhaust vent terminal for the horizontally vented gas fueled heating appliance 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 gas fueled equipment shall not approve the
installation unless, upon inspection, the inspector observes carbon monoxide 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 residential 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 installation of the equipment and the venting system shall
include:
1. Detailed instructions for the installation of the venting system design 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 provide the parts for venting the fl ue gases,
but identifi es “special venting systems,” the following requirements shall be satisfi ed by the manufacturer:
1. The referenced “special venting system” instructions shall be included 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 include 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 venting
instructions, all parts lists for venting instructions, and/or all venting design instructions shall remain with the appliance or
equipment at the completion of the installation.
5
GET TO KNOW YOUR WATER HEATER - GAS MODELS
A Vent Pipe–Exhaust
B Vent Terminal
C Vent Adapter-Rubber Boot
D Blower Assembly
E Cold Water Inlet
F Inlet Water Shut-off Valve
G Union
H Inlet Dip Tube
J Anode**
K Hot Water Outlet
L Outlet Receptacle (115 VAC)
M Temperature-Pressure Relief Valve
* ALL PIPING MATERIALS TO BE SUPPLIED BY CUSTOMERS.
** LOCATED UNDER THE BLOWER ASSEMBLY.
TYPICAL INSTALLATION
N Flue
O Flue Baffl e Assembly**
P Insulation
Q Control Harness
R Rating Plate
S Gas Supply
T Manual Gas Shut-off Valve
U Ground Joint Union
V Drip Leg (Sediment Trap)
W Drain Valve
X Gas Control Valve
Y Drain Pan
NATURAL HOT SURFACE IGNITER & MAIN BURNER
HOT
SURFACE
IGNITOR
Z Air Intake Screen - Base Pan
AA Inner Door
B B Outer Door
CC HSI Burner Assembly
D D Air Intake Screen Blower Assembly
E E FV Sensor/Bracket Assembly
(40K & 50K Models Only)
F F FV Sensor/Bracket Assembly
(55K & 62.5K Models Only)
SENSOR
*CAUTION: 115 VAC IN CONTROL HARNESS
AND INSIDE OUTER DOOR
PROPANE HOT SURFACE IGNITER & MAIN BURNER
HOT
SURFACE
IGNITOR
SENSOR
GAS CONTROL VALVE-THERMOSTAT
TEMPERATURE INDICATORS
TEMPERATURE ADJUSTMENT BUTTONS
GAS MODELS
WITH HOT SURFACE IGNITION
& 2", 3" OR 4" PVC VENT CAPABILITY
FIGURE 1.
6
TYPICAL INSTALLATION
MIXING VALVE USAGE
FIGURE 2.
This appliance has been design certifi ed as complying with American
National Standard/CSA Standard for water heaters and is considered
suitable for:
Water (Potable) Heating and Space Heating: All models are
considered suitable for water (potable) heating and space heating.
HOTTER WATER CAN SCALD:
Water heaters are intended to produce hot water. Water heated to a
temperature which will satisfy space heating, clothes washing, dish
washing, and other sanitizing needs can scald and permanently injure
you upon contact. Some people are more likely to be permanently
injured by hot water than others. These include the elderly, children,
the infi rm, or physically/mentally handicapped. If anyone using hot
water in your home fi ts into one of these groups or if there is a local
code or state law requiring a certain temperature water at the hot water
tap, then you must take special precautions. In addition to using the
lowest possible temperature setting that satisfi es your hot water needs,
a means such as a *Mixing Valve, should be used at the hot water taps
used by these people or at the water heater. Mixing valves are available
at plumbing supply or hardware stores. Consult a Qualifi ed Installer or
Service Agency. Follow mixing valve manufacturer’s instructions for
installation of the valves. Before changing the factory setting on the
thermostat, read the “Temperature Regulation” section in this manual,
see Figure 19.
7
LOCATING THE NEW WATER HEATER
FACTS TO CONSIDER ABOUT THE LOCATION
Carefully choose an indoor location for the new water heater, because
the placement is a very important consideration for the safety of
the occupants in the building and for the most economical use of
the appliance. This water heater is not for use in manufactured
(mobile) homes or outdoor installation.
Whether replacing an old water heater or putting the water heater in
a new location, the following critical points must be observed:
1. Select a location indoors as close as practical to the vent terminal
or location to which the water heater vent piping is going to be
connected, and as centralized with the water piping system as
possible.
2. Selected location must provide adequate clearances for servicing
and proper operation of the water heater.
Installation of the water heater must be accomplished in such a manner
that if the tank or any connections should leak, the fl ow will not cause
damage to the structure. For this reason, it is not advisable to install
the water heater in an attic or upper fl oor. When such locations cannot
be avoided, a suitable drain pan should be installed under the water
heater. Drain pans are available at your local hardware store. Such
a drain pan must have a minimum length and width of at least 2" (5.1
cm) greater that the water heater dimensions and must be piped to an
adequate drain. The pan must not restrict combustion air fl ow.
FIGURE 3.
Also, the water heater must be located and/or protected so it is not
subject to physical damage by a moving vehicle.
Water heater life depends upon water quality, water pressure and the
environment in which the water heater is installed. Water heaters are
sometimes installed in locations where leakage may result in property
damage, even with the use of a drain pan piped to a drain. However,
unanticipated damage can be reduced or prevented by a leak detector
or water shut-off device used in conjunction with a piped drain pan.
These devices are available from some plumbing supply wholesalers
and retailers, and detect and react to leakage in various ways:
• Sensors mounted in the drain pan that trigger an alarm or turn off
the incoming water to the water heater when leakage is detected.
• Sensors mounted in the drain pan that turn off the water supply to
the entire home when water is detected in the drain pan.
• Water supply shut-off devices that activate based on the water
pressure differential between the cold water and hot water pipes
connected to the water heater.
• Devices that will turn off the gas supply to a gas water heater while
at the same time shutting off its water supply.
INSTALLATIONS IN AREAS WHERE FLAMMABLE LIQUIDS
(VAPORS) ARE LIKELY TO BE PRESENT OR STORED (GARAGES,
STORAGE AND UTILITY AREAS, ETC.): Flammable liquids (such as
gasoline, solvents, propane (LP or butane, etc.) and other substances
(such as adhesives, etc.) emit fl ammable vapors which can be ignited
by a gas water heater’s hot surface igniter or main burner. The
resulting fl ashback and fi re can cause death or serious burns to anyone
in the area. This water is equipped with a FV sensor for detecting the
presence of fl ammable vapors, see Figure 3. When the sensor detects
those vapors, the unit will shut down and not operate. Should this
happen, please refer to the troubleshooting guide on pages 28-30.
Even though this water heater is a fl ammable vapors ignition resistant
water heater and is designed to reduce the chances of fl ammable
vapors being ignited, gasoline and other fl ammable substances should
never be stored or used in the same vicinity or area containing a gas
water heater or other open fl ame or spark producing appliance.
This water heater must not be installed directly on carpeting. Carpeting
must be protected by metal or wood panel beneath the appliance
extending beyond the full width and depth of the appliance by at least
3" (7.6 cm) in any direction, or if the appliance is installed in an alcove
or closet, the entire fl oor must be covered by the panel. Failure to
heed this warning may result in a fi re hazard.
Minimum clearances between the water heater and combustible
construction are 0 inch at the sides and rear, 5" (12.7 cm) from the front
8
and 12" (30.5 cm) from the top. (Standard clearance.) If clearances
stated on the heater differ from standard clearances, install water
heater according to clearances stated on the heater.
Adequate clearance for servicing this appliance should be considered
before installation, such as changing the anodes, etc.
chlorine based chemicals, refrigerants, etc.) in addition to being highly
fl ammable in many cases, will also react to form corrosive hydrochloric
acid when exposed to the combustion products of the water heater.
The results can be hazardous, and also cause product failure.
INSULATION BLANKETS
A minimum clearance of 5" (12.7 cm) must be allowed for access
to replaceable parts such as the thermostats, drain valve and relief
valve.
When installing the heater, consideration must be given to proper
location. Location selected should be as close to the wall as practicable
and as centralized with the water piping system as possible.
FIGURE 4.
A gas water heater cannot operate properly without the correct amount
of air for combustion. Do not install in a confi ned area such as a closet,
unless you provide air as shown in the “Locating The New Water
Heater” section. Never obstruct the fl ow of ventilation air. If you have
any doubts or questions at all, call your gas supplier. Failure to provide
the proper amount of combustion air can result in a fi re or explosion
and cause death, serious bodily injury, or property damage.
Insulation blankets are available to the general public for external use
on gas water heaters but are not necessary with these products. The
purpose of an insulation blanket is to reduce the standby heat loss
encountered with storage tank heaters. Your water heater meets or
exceeds the National Appliance Energy Conversation Act standards
with respect to insulation and standby loss requirements, making an
insulation blanket unnecessary.
Should you choose to apply an insulation blanket to this heater, you
should follow these instructions (For identifi cation of components
mentioned below, see Figure 1). Failure to follow these instructions
can restrict the air fl ow required for proper combustion, potentially
resulting in fi re, asphyxiation, serious personal injury or death.
FIGURE 5.
If this water heater will be used in beauty shops, barber shops, cleaning
establishments, or self-service laundries with dry cleaning equipment, it
is imperative that the water heater or water heaters be installed so that
combustion and ventilation air be taken from outside these areas.
Propellants of aerosol sprays and volatile compounds, (cleaners,
• Do not apply insulation to the top of the water heater, as this will
interfere with safe operation of the draft hood.
• Do not cover the outer door, thermostat or temperature & pressure
relief valve.
• Do not allow insulation to come within 2" (5.1 cm) of the fl oor to
prevent blockage of combustion air fl ow to the burner.
• Do not cover the instruction manual. Keep it on the side of the
water heater or nearby for future reference.
• Do obtain new warning and instruction labels from the manufacturer
for placement on the blanket directly over the existing labels.
• Do inspect the insulation blanket frequently to make certain it
does not sag, thereby obstructing combustion air fl ow.
COMBUSTION AIR AND VENTILATION FOR
APPLIANCES LOCATED IN UNCONFINED SPACES
UNCONFINED SPACE is space whose volume is not less than
50 cubic feet per 1,000 Btu per hour (4.8 cubic meters per kW) of the
aggregate input rating of all appliances installed in that space. Rooms
communicating directly with the space in which the appliances are
installed, through openings not furnished with doors, are considered
a part of the unconfi ned space.
In unconfi ned spaces in buildings, infi ltration may be adequate to
provide air for combustion, ventilation and dilution of fl ue gases.
However, in buildings of tight construction (for example, weather
stripping, heavily insulated, caulked, vapor barrier, etc.), additional air
may need to be provided using the methods described in “Combustion
Air and Ventilation for Appliances Located in Confi ned Spaces.”
COMBUSTION AIR AND VENTILATION FOR
APPLIANCES LOCATED IN CONFINED SPACES
CONFINED SPACE is a space whose volume is less than 50 cubic
feet per 1,000 Btu per hour (4.8 cm per kW) of the aggregate input
rating of all appliances installed in that space.
9
Chemical vapor corrosion of the fl ue, blower assembly and vent
system may occur if air for combustion contains certain chemical
vapors. Spray can propellants, cleaning solvents, refrigerator and
air conditioner refrigerants, swimming pool chemicals, calcium and
sodium chloride, waxes, bleach and process chemicals are typical
compounds which are potentially corrosive.
A. ALL AIR FROM INSIDE BUILDINGS: (See Figure 5 and 6)
The confi ned space shall be provided with two permanent openings
communicating directly with an additional room(s) of suffi cient volume
so that the combined volume of all spaces meets the criteria for an
unconfi ned space. The total input of all gas utilization equipment
installed in the combined space shall be considered in making this
determination. Each opening shall have a minimum free area of one
square inch per 1,000 Btu per hour (22 cm
all gas utilization equipment in the confi ned space, but not less than 100
square inches (645 cm
2
). One opening shall commence within 12 inches
2
/kW) of the total input rating of
(31 cm) of the top and one commencing within 12 inches (31 cm) of
the bottom of the enclosures.
FIGURE 8.
4. When ducts are used, they shall be of the same cross-sectional
area as the free area of the openings to which they connect. The
minimum short side dimension of rectangular air ducts shall not
be less than 3 inches (7.6 cm), see Figure 9.
FIGURE 6.
B. ALL AIR FROM OUTDOORS: (See Figures 7, 8 and 9)
The confi ned space shall be provided with two permanent openings,
one commencing within 12 inches (31 cm) of the top and one
commencing within 12 inches (31 cm) from the bottom of the
enclosure. The openings shall communicate directly, or by ducts,
with the outdoors or spaces (crawl or attic) that freely communicate
with the outdoors.
1. When directly communicating with the outdoors, each opening shall
have a minimum free area of 1 square inch per 4,000 Btu per hour
2
(5.5 cm
/kW) of total input rating of all equipment in the enclosure,
see Figure 7.
FIGURE 7.
2. When communicating with the outdoors through vertical ducts, each
opening shall have a minimum free area of 1 square inch per 4,000
Btu per hour (5.5 cm
2
/kW) of total input rating of all equipment in
the enclosure, see Figure 8.
FIGURE 9.
5. Alternatively a single permanent opening may be used when
communicating directly with the outdoors, or with spaces that freely
communicate with the outdoors. The opening shall have a minimum
free area of 1 square inch per 3,000 BTU per hour (8.3 cm
2
/kW)
of total input rating of all equipment in enclosure. See Figure 9A.
FIGURE 9A.
6. Louvers and Grilles: In calculating free area, consideration shall be
given to the blocking effect of louvers, grilles or screens protecting
openings. Screens used shall not be smaller than 1/4 inch
(6.4 mm) mesh. If the free area through a design of louver or
grille is known, it should be used in calculating the size opening
required to provide the free area specifi ed. If the design and free
area is not known, it may be assumed that wood louvers will be
20-25 percent free area and metal louvers and grilles will have
60-75 percent free area. Louvers and grilles shall be fi xed in the
open position or interlocked with the equipment so that they are
opened automatically during equipment operation.
3. When communicating with the outdoors through horizontal ducts,
each opening shall have a minimum free area of 1 square inch
per 2,000 Btu per hour (11 cm
2
/kW)) of total input rating of all
equipment in the enclosure, see Figure 9.
7. Special Conditions Created by Mechanical Exhausting or Fireplaces:
operation of exhaust fans, ventilation systems, clothes dryers or
fi replaces may create conditions requiring special attention to avoid
unsatisfactory operation of installed
10
gas utilization equipment.
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