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Provisions for Adequate Combustion and Ventilation Air
This heater shall not be installed in a “ CONFINED SPACE” or unusually tight construction unless provi-
sions are provided for adequate combustion and ventilation air.
The NATIONAL FUEL GAS CODE, ANSI Z223.1/NFPA 54 defines a “CONFINED SPACE” as a space
whose volume is less than 50 cubic feet per 1000 BTU per hour (4.8m
3
per kw) of the aggregate input
rating of all appliances installed in that space, and an “UNCONFINED SPACE” as a space whose volume
is not less than 50 cubic feet per 1000 BTU per hour (4.8m
3
per kw) of the aggregate input rating of all
appliances installed in that space. Rooms communicating directly with the space in which the appliances
are installed, through openings not furnished with doors, are considered a part of the unconfined space.
Determining if You Have Adequate Combustion and Ventilation Air in Your Space
1. Determine the volume of space,
(length x width x height)
. Include adjoining rooms connected by
doorless passageways or ventilation grilles.
Example: A room that is 25’ x 18’ x 8’ has a volume of 3,600 cubic feet. If additional ventilation
to adjoining rooms is supplied with grilles or openings, add the volume of these rooms to the
total volume of the space.
2. Divide the volume of space by 50 cubic feet. The result is the maximum BTU/Hr the unconfined space
can support.
Example: 3,600 cubic feet divided by 50 = 72 or 72,000 BTU/Hr (maximum Btu/Hr the space can
support.)
3. Add the BTU/Hr ratings of all fuel-burning appliances installed in the same space. NOTE: Do not
include direct vent appliances as these utilize outside air for combustion and vent to the outdoors.
Example: Gas range (55,000 BTU/Hr) + Vent Free Heater (39,000 BTU/Hr) = Total 80,000 BTU/Hr.
4. Compare the maximum BTU/Hr rating the space can support with the total BTU/Hr used by the
appliances.
Example: 72,000 BTU/Hr - Max. the space can support. 94,000 BTU/Hr - Total used by the
appliances. In this example, the minimum BTU/Hr the space can support is less than the total
BTU/Hr used by the appliances. The space is considered “CONFINED SPACE”. Additional air
must be provided to meet the requirements of the vent free heater.
If you have no other fuel burning appliances located in the space, then the minimum necessary space you
would need for this 39,000 BTU/Hr maximum heater is 1950 cu. ft. An example of such a room would be
one with a length of 22’, width of 12’, and a standard 8’ ceiling - 22’ x 11.5’ x 8’ = 2,024 cubic feet.
WARNING
If the area in which the heater may be operated is smaller than that defined as an unconfined space or if
the building is of unusually tight construction, provide adequate combustion and ventilation air by one of the
methods described in the National Fuel Gas Code, ANSI Z223.1/NFPA 54.