Combustion Air And Ventilation

A gas water heater cannot operate properly without the correct amount of air for combustion. Do not install in a conﬁned area such as a closet, unless you provide air as shown in the “Facts to Consider About Location” section. Never obstruct the ﬂow 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 ﬁre or explosion and cause death, serious bodily injury, or property damage.

FIGURE 10

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(s) be installed so that all air for combustion and ventilation is taken from outdoors.

Note: Vent length should be long enough that the outside air will not freeze the water heater.

Propellants of aerosol sprays and volatile compounds, (cleaners, chlorine based chemicals, refrigerants, etc.) in addition to being highly ﬂammable 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.

APPLIANCES 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 unconﬁned space.

In unconﬁned spaces in buildings, inﬁltration may be adequate to provide air for combustion, ventilation and dilution of flue 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 “Appliances in Conﬁned Space” that follows.”

APPLIANCES IN CONFINED SPACES

CONFINED SPACE is a space whose volume is less than 50 cubic feet per 1,000 Btu per hour (4.8cm per kW) of the aggregate input rating of all appliances installed in that space.

When drawing combustion air from inside a building to a conﬁned space, such a space should be provided with two permanent openings. ONE WITHIN 12 in. (30cm) OF THE ENCLOSURE TOP AND ONE WITHIN 12 in. (30cm) OF THE ENCLOSURE BOTTOM. Each opening should have a free area of 1 square inch per 1000 Btu/hr (22 cm2/kW) of the total input of all appliances in the enclosure, but not less than 100 square in. (645 cm2).

If the conﬁned space is within a building, air for combustion and ventilation must be obtained from outdoors. When directly communicating with the outdoors or communicating through vertical ducts, two permanent openings, located in the above manner, should be provided. Each opening should have a free area of not less than 1 square inch per 4000 Btu/hr (5.5 cm2/kW) of total input of all appliances in the enclosure. If horizontal ducts are used, each opening should have a free area of not less than 1 square inch per 2000 Btu/hr (11 cm2/kW) of the total input of all appliances in the enclosure.

A.ALL AIR FROM INSIDE BUILDINGS: (See Figures 10 & 11)

The conﬁned space should be provided with two permanent openings communicating directly with an additional room(s) of sufﬁcient volume so that the combined volume of all spaces meets the criteria for an unconﬁned space. The total input of all gas utilization equipment installed in the combined space should be considered in making this determination. Each opening should have a minimum free area of 1 square inch per 1,000 Btu per hour (22 cm2/kW) of the total input rating of all gas utilization equipment in the conﬁned space, but not less than 100 square in. (645 cm2). One opening should commence within 12 in. (30cm) of the top and one commencing within 12 in. (30cm) of the bottom of the enclosures.

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