Raypak 399B-2339B Operations Instructions download pdf (Page 13)

space shall be considered in making this determina-

tion. Each opening shall have a minimum free area of

1 in.

per 1,000 BTUH (2,225 mm

per kW) of the total

input rating of all gas utilization equipment in the con-

fined space, but not less than 100 in.

(645 cm

). One

opening shall commence within 12 in. (305 mm) of the

top, and one opening shall commence within 12 in.

(305 mm) of the bottom of the enclosure. The mini-

mum dimension of air openings shall be not less than

3 in. (76 mm) in any direction.

All Air from Outdoors

The confined space shall communicate with the out-

doors in accordance with one of the methods below.

The minimum dimension of air openings shall not be

less than 3 in. (76 mm) in any direction. Where ducts

are used, they shall be of the same cross-sectional

area as the net free area of the openings to which they

connect.

1. Two permanent openings, one commencing

within 12 in. (305 mm) of the top, and one com-

mencing within 12 in. (305 mm) of the bottom of

the enclosure, shall be provided. The openings

shall communicate directly, or by ducts, with the

outdoors or spaces (crawl or attic) that freely com-

municate with the outdoors.

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.

per

4,000 BTUH (550 mm

per kW) of total input

rating 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.

per 2,000

BTUH (1,100 mm

per kW) of total input rat-

ing of all equipment in the enclosure.

2. One permanent opening, commencing within 12

in. (305 mm) of the top of the enclosure, shall be

permitted where the equipment has clearances of

at least 1 in. (25 mm) from the sides and back and

6 in. (152 mm) 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 that

freely communicate with the outdoors, and shall

have a minimum free area of:

a. 1 in.

per 3,000 BTUH (740 mm

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 gas-fired appliances.

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 the outdoors. The total cross-sectional area of

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

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

shall the cross-sectional area be less than 10 in.

(65 cm

2. For heaters using a barometric damper in the vent

system there shall be a permanent air supply

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

than 1 in.

per 7,000 BTUH (320 mm

per kW) up

to and including 1 million BTUH, plus 1 in.

per

14,000 BTUH (160 mm

per kW) in excess of 1

million BTUH. This opening(s) shall be either

located at or ducted to a point not more than 18 in.

(450 mm) nor less than 6 in. (152 mm) above the

floor level. The duct can also “goose neck” through

the roof. The duct is preferred to be straight down

and terminated 18 in. (450 mm) from the floor, but

not near piping. This air supply opening require-

ment shall be in addition to the air opening for

ventilation air required in 1. (above).

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 cross-sectional area

CAUTION: All combustion air must be drawn from

the air outside of the building; the mechanical equip-

ment room must communicate directly with the

outdoors.

Canadian Installations

WARNING: Care must be taken to ensure that the

equipment room is not under negative pressure

conditions or that the equipment is not common-

vented with other gas-fired appliances.

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Raypak 399B-2339B Operations Instructions Page 13

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