a.Where directly communicating with the out- doors or where communicating to the outdoors through vertical ducts, each opening shall have a minimum free area of 1 in.2 per 4000 BTUH (5.5 cm2 per kW) of total input rat- ing of all equipment in the enclosure.
b.Where communicating with the outdoors through horizontal ducts, each opening shall have a minimum free area of 1 in.2 per 2000 BTUH (11 cm2 per kW) of total input rating of all equipment in the enclosure.
2.One permanent opening, commencing within 12 in. (30 cm) of the top of the enclosure, shall be permitted where the equipment has clearances of at least 1 in. (2.5 cm) from the sides and back and 6 in. (16 cm) from the front of the appliance. The opening shall directly communicate with the out- doors or shall communicate through a vertical or horizontal duct to the outdoors or spaces (crawl or attic) that freely communicate with the outdoors, and shall have a minimum free area of:
a.1 in.2 per 3000 BTUH (7 cm2 per kW) of the total input rating of all equipment located in the enclosure, and
b.Not less than the sum of the areas of all vent connectors in the confined space.
WARNING: Do not use one permanent opening method if the equipment room is under negative pressure conditions or the equipment is common vented with other
Installations in Canada
CAUTION: All combustion air must be drawn from the air outside of the building; the mechanical equipment room must communicate directly with the outdoors.
1.Ventilation of the space occupied by the heater shall be provided by an opening(s) for ventilation air at the highest practical point communicating with outdoors. The total
2.For heaters using a barometric damper in the vent system, and when air supply is provided by natu-
ral air flow from the outdoors for natural draft, par- tial fan assisted,
3.For heaters not using a barometric damper in the vent system, and when air supply is provided by natural air flow from outdoors for a power burner and there is no draft regulator, drafthood or similar flue gas dilution device installed in the same space, in addition to the opening for ventilation air required in (1), there shall be a permanent air sup- ply opening(s) having a total
4.Refer to the latest version of the B149 for addition- al information.
Water Piping
General
The heater should be located so that any water leaks will not cause damage to the adjacent area or struc- tures.
CAUTION: This heater requires forced water circulation when the burner is operating. See Table E and Table F for minimum and maximum flow rates and water pump selection. The pump must be interlocked with the heater to prevent heater operation without water circulation.
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