A.O. Smith Residential Power Vent Gas Water Heaters with Hot Surface Ignition instruction manual

Locating the New Water Heater (cont’d)

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 of the aggregate input rating of all appliances installed in that space.

a.ALL AIR FROM INSIDE BUILDINGS: (See Page 8 Figure 1, and Figure 6 below)

The confined space shall 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 shall be considered in making this determination. Each open- ing shall have a minimum free area of one square inch per 1,000 BTU per hour of the total input rating of all gas utiliza- tion equipment in the confined space, but not less than 100 square inches. One opening shall commence within 12 inch- es of the top and one commencing within 12 inches of the bottom of the enclosure.

VENT THROUGH

ROOF

VENT TO

OUTDOORS

OPENINGSWATER

HEATER

Figure 6

b. ALL AIR FROM OUTDOORS: (see Figures 7-9)

The confined space shall be provided with two permanent openings, one commencing within 12 inches of the top and one commencing within 12 inches 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.

VENTILATION LOUVERS		VENT THROUGH
(each end of attic)
			ROOF
			VENT TO
			OUTDOORS
	INLET AIR	WATER
		HEATER
	DUCT

Figure 7

VENTILATION LOUVERS

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 of total input rating of all equip- ment in the enclosure. (See Figure 6.)

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 of total input rating of all equipment in the enclosure. (See Figure 8.)

VENTILATION LOUVERS

(each end of attic)

		VENT THROUGH ROOF
	AIR OUTLET		VENT TO
			OUTDOORS
		WATER
INLET AIR DUCT		HEATER
(ends 1″ above floor)

Figure 8

3.When communicating with the outdoors through horizon- tal ducts, each opening shall have a minimum free area of 1 square inch per 2,000 BTU per hour of total input rating of all equipment in the enclosure. (See Figure 9.)

VENT THROUGH

ROOF

VENT TO

OUTDOORS

OUTLET AIR DUCT

INLET AIR DUCT

Figure 9

4.When ducts are used, they shall be of the same cross-sec- tional 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. (See Figure 9.)

5.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 small- er than 1⁄4 inch mesh. If the free area through a design of lou- ver or grille is known, it should be used in calculating the size opening required to provide the free area specified. 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 fixed in the open position or interlocked with the equipment so that they are opened automatically during equipment operation.

6.Special Conditions Created by Mechanical Exhausting or Fireplaces: Operation of exhaust fans, ventilation systems, clothes dryers or fireplaces may create conditions requiring special attention to avoid unsatisfactory operation of installed gas utilization equipment.

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