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rooms together. Repeat for any other connected rooms which do not have doors. Do not add the volume of two rooms
separated by a door even if that door is "always left open".
3) Divide the volume obtained in Step 2 by the input calculated in Step 1.
4) If the result is at least 50 ft
tration should provide adequate fresh air into the boiler room.
5) If the result is less than 50 ft
near the ceiling. The top edge of the upper opening must be within 12" of the ceiling and the bottom edge of the lower
opening must be within 12" of the floor (Figure 5.1):
•
Each opening must have a free area of 1 square inch per 1000 BTU/hr input of all gas burning appliances in the
boiler room. The minimum opening dimension is 3 inches. Minimum opening free area is 100 square inches per
opening.
•
If the total volume of both the boiler room and the room to which the openings connect is less than 50 cubic feet
per 1000 BTU/hr of total appliance input, install a pair of identical openings into a third room. Connect additional
rooms with openings until the total volume of all rooms is at least 50 cubic feet per 1000 BTU/hr of input.
•
The "free area" of an opening takes into account the blocking effect of mesh, grills, and louvers. Where screens are
used, they must be no finer than ¼" (4 x 4) mesh.
•
If providing openings into adjacent rooms is undesirable, use the Outdoor Combustion Air Method.
6) Do not use the Indoor Combustion Air Method described above if either of the following are true:
a.
The indoor space is so tightly constructed that the number of air changes per hour is known to be 0.4 or less.
b. The boiler room is depressurized relative to the outdoors. This depressurization is possible if the structure is
tightly constructed and/or is equipped with exhaust fans.
Example:
An AWR105EN and a water heater are to be installed in a room measuring 6 ft - 3 in x 7 ft with an 8 ft ceiling. The
water heater has an input of 30000 BTU/hr:
Total input in thousands of BTU/hr = (105000 BTU/hr + 30000 BTU/hr) ÷ 1000 = 135
Volume of room = 6.25 ft x 7 ft x 8 ft = 350 ft
FIGURE 5.1: INDOOR COMBUSTION AIR METHOD
per 1000BTU/hr, and neither of the conditions described in (6) below are met, normal infil-
3
per 1000BTU/hr, provide two openings into the boiler room, one near the floor and one
3
3
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