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APPENDIX A – COMBUSTION AIR
PROVIDE ENOUGH AIR to ventilate the
boiler room, dilute the ue gases, and
sustain combustion. Ignition failure, overheating,
re, carbon monoxide, and spillage of ue gases
may result from poor air supply.
If the boiler is a Direct Vent boiler and exchanges
all combustion air and combustion products
directly with the outdoors, there are no special
requirements for providing combustion, ventilation,
and dilution air.
If the boiler is chimney vented, power vented or
induced draft and draws combustion air from within
the building, follow the steps below to determine
how to provide air to the boiler.
Is the boiler located in a conned space?:
1. Calculate the oorspace (in square feet) of
the boiler room and all rooms connected
to the boiler room by passageways not
furnished with doors.
___________ floorspace (sq. ft.)
2. Add up the input rates of all the combustion
appliances installed in the same oorspace.
combined appliance
___________ input (BTU/hr)
3. In the table below, nd the Minimum
Allowable Floorspace based on the
Combined Input Rate from Step 2 and the
ceiling height. If the Combined Input Rate
is between two rates, use the next highest
rate.
minimum allowable
___________ floorspace (sq. ft.)
4. If the Floorspace from Step 1 is less than the
Minimum Floorspace from Step 3, then you
must provide outdoor air to the boiler room.
Proceed to Step 6.
Is the boiler located in a building of unusually tight
construction?
5. If the answer to all of the three questions
below is “yes”, then you must provide
outdoor air to the boiler room.
Do the walls and ceilings exposed to the
outside atmosphere have a continuous
water vapor retarder with a rating of 1 perm
or less, with openings gasket or sealed?
Yes No
Are operable windows and doors
weatherstripped?
Yes No
Are exterior wall joints caulked or sealed?
Yes No
6. If you must provide outdoor air to the boiler
room, the top of the permanent opening
into the boiler room must be within 12” of
the ceiling, and the free area of the opening
(sq. in.) must be no less than the Combined
Appliance Input (from Step 2) divided by
3000 BTU/hr/sq. in.
combined appliance
__________ input (Step 2)
÷ 3000 BTU/hr/sq. in.
Minimum Opening Size
_____ (sq. in.)
7. Duct this opening vertically or horizontally
directly to the outdoors, or directly to a
space that communicates directly with the
outdoors, such as an attic or crawlspace.
Minimum Allowable Floorspace in the Boiler Room
and Freely Connected Rooms (sq. ft.)
Ceiling Height
7’ 8’ 9’ 10’
Combined
Appliance
Input Rate
(see Step 2)
(BTU/hr)
50,000 357 313 278 250
100,000 714 625 556 500
150,000 1071 938 833 750
200,000 1429 1250 1111 1000
250,000 1786 1563 1389 1250
300,000 2143 1875 1667 1500
350,000 2500 2188 1944 1750
400,000 2857 2500 2222 2000
For more details and options, refer to your local
building code, the National Fuel Gas Code (NFPA
54 and ANSI Z223), and the Canadian Natural Gas
Installation Code CAN/CGA-B149.1 or Propane
Installation Code CAN/CGA-B149.2.