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MECHANICAL EXHAUSTING OF ROOM AIR
1. Where an exhaust fan is installed in the same room with this water heater and combustion air is drawn from
inside the room, sufficient openings for air must be provided in the walls. UNDERSIZED OPENINGS WILL
CAUSE AIR TO BE DRAWN INTO THE ROOM THROUGH THE WATER HEATER’S VENTING SYSTEM,
CAUSING POOR COMBUSTION THAT MAY BE HAZARDOUS TO LIFE. SOOTING MAY RESULT IN
SERIOUS DAMAGE TO THE WATER HEATER AND RISK OF FIRE OR EXPLOSION, WHICH CAN ALSO
CREATE A RISK OF ASPHYXIATION. Refer to local codes and /or National Fuel Gas Code for proper air
opening sizing.
UNCONFINED SPACE
1. In buildings of conventional frame, brick or stone construction, unconfined spaces may provide adequate air
for combustion and ventilation.
2. If the unconfined space is within a building of tight construction (buildings using the following construction:
weather stripping, heavy insulation, caulking, vapor barrier, etc.), air for combustion and ventilation must be
obtained from outdoors. This may be accomplished by piping air directly to the water heater from outside or
providing opening or ducts in the wall. The installation instructions for confined spaces in tightly constructed
buildings must be followed to ensure adequate air supply.
CONFINED SPACE
1. When drawing combustion air from inside a conventionally constructed building to a confined space, such a
space must be provided with two permanent openings.
The top opening is to be located within 12 inches (30.5 cm) of the enclosure top and the bottom
opening within 12 inches (30.5 cm) of the enclosure bottom.
Each opening must have a free area of at least 1 inch² (6.5 cm²) per 1000 Btu/h (.3 kw) of the total input
of all appliances in the enclosure, but not less than 100 inches² (645.2 cm²).
2. If the confined space is within a building of tight construction, air for combustion and ventilation must be
obtained from outdoors. This may be accomplished by piping air directly to the water heater from outside or
providing opening or ducts in the wall. When directly communicating with the outdoors through vertical ducts,
two permanent openings, located in the above manner, must be provided.
Each opening must have a free area of not less than 1 inch² (6.5 cm²) per 4000 Btu/h (1.2 kw) of the
total input of all appliances in the enclosure.
If horizontal ducts are used, each opening must have a free area of not less than 1 inch² (6.5 cm²) per
2000 Btu/h (.6 kw) of the total input of all appliances in the enclosure.
3. If the water heater is installed as a direct vent (outside air piped directly to the water heater), then additional
opening, other than the opening for the air intake, are not required. However, adequate ventilation air must be
provided in all cases to prevent increased room temperature.
CHEMICAL VAPOR CORROSION
Corrosion of the flue ways and vent system will occur if air for combustion contains certain chemical vapors. Such
corrosion may result in poor combustion and create a risk of asphyxiation, as well as reducing the life of the water
heater. Spray can propellants, cleaning solvents, refrigerator and air conditioning refrigerants, swimming pool
chemicals, calcium and sodium chloride, waxes and process chemicals are corrosive. Products of this sort should
not be stored near the water heater or outside by the air intake (if applicable).
TYPICAL INSTALLATION ILLUSTRATION
CAUTION
If the building cold water supply has a back-flow preventer, check valve, or water meter with check valve,
provisions for thermal expansion of water in the hot water system must be provided.