Raypak 751 Operations Instructions download pdf (Page 11)

Conventional Combustion Air

Supply

U.S. Installations

All Air from Inside the Building

If all combustion air is drawn from the air inside the

building (the mechanical equipment room does not

receive air from outside):

1. The mechanical equipment room must be provid-

ed with two permanent openings communicating

directly with additional room(s) of sufficient volume

so that the combined volume of all spaces meets

the criteria for an unconfined space. (An uncon-

fined space is defined as a space whose volume

is more than 50 cubic feet per 1,000 BTUH of the

aggregate input rating of all appliances installed in

that space.)

2. Each opening must have a minimum free area of

one (1) square inch per 1,000 BTUH of the total

input rating of all gas utilization equipment in the

mechanical equipment room.

3. One opening must commence within twelve (12)

inches of the top, and one opening must com-

mence within twelve (12) inches of the bottom of

the room.

4. Refer to NFGC, Part 5, for additional information.

All Air from Outdoors

If all combustion air is drawn from the air outside the

building (the mechanical equipment room directly

communicates with the outdoors), either of the follow-

ing two methods can be used:

Method 1:

1. The mechanical equipment room must be provid-

ed with two permanent openings, one

commencing within (twelve) 12 inches of the top,

and one commencing within twelve (12) inches of

the bottom of the room.

2. The openings must communicate directly, or by

ducts, with the outdoors.

3. Each opening must have a minimum free area of

one (1) square inch per 4,000 BTUH of total input

rating of all equipment in the room when the open-

ing is communicating directly with the outdoors or

through vertical ducts. The minimum free area

required for horizontal ducts is one (1) square inch

per 2,000 BTUH of total input rating to all the

equipment in the room.

4. Refer to NFGC, Part 5, for additional information.

Refer to Appendix A for additional information

about combustion air quality.

Method 2 (normally applied in cold climate regions):

1. The mechanical equipment room must be provid-

ed with at least one permanent opening,

commencing within 12 inches of the top of the

enclosure.

2. The opening must communicate directly or by

ducts with outdoors.

3. The opening must have a minimum free area of 1

sq. in per 3000 BTUH of the total input rating of all

equipment in the room, or no less than the sum of

the areas of all vent connectors in the confined

space. Refer to the latest version of NFGC, part 5

for additional information.

1. Ventilation of the space occupied by the boiler

shall be provided by an opening(s) for ventilation

air at the highest practical point communicating

with outdoors. The total cross-sectional area of

such an opening(s) shall be at least 10% of the

area required in (2) and (3), but in no case shall

the cross-sectional area be less than 10 square

inches (6500 square mm).

2. When air supply is provided by natural air flow

from the outdoors for natural draft, partial fan

assisted, fan-assisted or power draft-assisted

burners, there shall be a permanent air supply

opening(s) having a cross section area of not less

than 1 sq. in. per 7000 BTUH (310 sq. mm per kW)

up to and including 1 million BTUH, plus 1 sq. in.

per 14000 BTUH (155 sq. mm per kW) in excess

WARNING: Do not use one permanent opening

method (Method 2) if the equipment room is under

negative pressure condition or the equipment is

common vented with other gas-fired appliances.

Canadian Installations

CAUTION: All combustion air has to be drawn from

the air outside the building (the mechanical

equipment room directly communicates with the

outdoors).

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Raypak 751 Operations Instructions Page 11

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