COMBUSTION AIR
VENTILATION AIR
NOTE: All ducts must have the same cross sec- tional area as the free area of each opening to which they connect. The minimum side dimension of a rec- tangular duct must be no smaller than three (3) inches.
Caution: Operation of exhaust fans, ventiliating sys- tems, power burn- ers, induced draft systems, or fire- places may create conditions that require special attention to avoid unsatisfactory operation of installed equip- ment.
Adequate,
In a confined space with a volume of less than 50 cubic feet per 1000 BTUH, the space must be vented at the floor for combustion air, and at the ceiling for ventilation. The air can be supplied from either inside or outside of the building as conditions allow.
Care must be taken to insure an adequate air supply for the water heater.
A. Install equipment only where the water heater will have satisfactory combustion, proper venting and the maintenance of temperature at safe limits all around the unit under normal operating condi- tions. Free circulation of air around the water heater is essential. If the air supply is inadequate, introduce outside air. Any temperature above 90°F around the heater indicates a need for additional air (see NFPA 31 for air requirements).
B. In addition to air needed for combustion, air may be required for draft control; cooling off; control- ling dew point; heating; drying; oxidation or dilution; safety exhaust; odor control; and compressors.
C. Make sure air around the water heater is adequate for personal comfort and working conditions.
D. Check for proper draft. Place a draft gauge in the chimney above the draft diverter. Drafts should be at least
Unconfined space: No additional combustion and ventilation air is required if the volume of the space is greater than 50 cubic feet per 1,000 BTUH of the combined total input of all equipment installed in that space. Rooms leading directly to the space through openings which cannot be closed are considered part of the unconfined space.
Confined space: When the unit will be installed in a space with a volume of less than 50 cubic feet per 1,000 BTUH, the space must be vented at the floor for combustion air and at the ceiling for venti- lation. This air can be supplied from either inside or outside of the building as conditions allow (refer to NFPA 31 or local codes).
A. Inside air supply: Provide two permanent openings; one within 12” of the top of the enclosure and one within 12” of the bottom, leading directly to room(s) of sufficient volume so that the combined volume of all the space meets the criteria for unconfined space. Each opening required a minimum free area of one (1) square inch (two square inches total) per 1,000 BTUH of the combined total input of all equipment installed in the enclosure, but not less than 100 square inches.
B. Outside air supply: Provide two permanent openings; one within 12” of the top of the enclosure and one within 12” of the bottom. These openings must lead directly to crawl and attic spaces lead- ing directly to the outside of the building.
1.Leading directly to outside or through vertical ducts: Each opening (top and bottom) requires a minimum free area of one (1) square inch (two square inches total) per 4,000 BTUH of the combined total input of all equipment installed in the enclosure.
2.Leading to the outside through horizontal ducts: Each opening (top and bottom) requires a mini- mum free area of one (1) square inch (two square inches total) per 2,000 BTUH of the combined total input of all equipment in the enclosure.
Louvers and grilles: In calculating the “free” area in Equipment Located in Confined Spaces, consider the blocking effects of louvers, grilles, or screens protecting openings. The screens cannot be smaller than one (1) inch of mesh. If the “free” area of a louver 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, assume wood louvers have 20% to 25% “free” area, and metal louvers and grilles 60& to 70%. Fix louvers and grilles in the open position or interlock with the equipment so they are opening automatically during equipment operation.
