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2.
Divide the space volume by 50 cubic feet to determine the maximum BTU/hr the space can support.
Example: 2560 cu. ft. (volume of space) ÷ 50 cu. ft. = 51.2 or 51,200(maximum BTU/hr the space can support)
Add the BTU/hr of all fuel burning appliances in the space.
Vent-free heater
Gas water heater*
Gas furnace
Vented gas heater
Gas heater logs
Other gas appliances* +
Total
*Do not include direct-vent gas appliances. Direct-vent draws combustion air from the outdoors and vents to
the outdoors.
4.
Compare the maximum BTU/hr that the space can support with the actual amount of BTU/hr used.
Example: 51,200 BTU/hr (maximum the space can support)
56,000 BTU/hr (actual amount of Btu/Hr used)
The space in the above example is a confined space because the actual BTU/hr used is more than the
maximum BTU/hr the space can support. You must provide additional fresh air. Your options are as follows:
a) Rework worksheet, adding the space of an adjoining room. If the extra space provides an unconfined
space, remove door to adjoining room or add ventilation grills between rooms. See "Ventilation Air from
Outdoors," page 9.
b) Vent room directly to the outdoors. See "Ventilation Air from Outdoors," page 9.
c) Install a lower BTU/hr heater, if lower BTU/hr size makes room unconfined. If the actual Btu/Hr used is
less than the maximum Btu/Hr the space can support, the space is an unconfined space. You will need no
additional fresh air ventilation.
Warnning: 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, ANS Z223.1/ NFPA, air for combustion and
ventilation or applicable local codes.
WARNING: If the area in which the heater may be operated does not meet the required volume for indoor
combustion air, combustion and ventilation air shall be provided by one of the methods described in the
NATIONAL FUEL GAS CODE, ANSI Z223.1/NFPA 54, the INTERNATIONAL FUEL GAS CODE, or applicable
local codes.
Ventilation Air From lnside Building
This fresh air would come from an adjoining unconfined
space. When ventilating to an adjoining unconfined
space, you must provide two permanent openings:
"
one within 12
of the ceiling and one within 12
floor on the wall connecting the two spaces (see
options 1 and 2, Figure 2). You can also remove door
into adjoining room (see option 3, Figure 2). Follow the
National Fuel Gas Code. NFPA 54/ANSI Z223.1.
Air for Combustion and Ventilation for required
size of ventilation grills or ducts.
(Volume of space) ÷ 50 cu. ft. = (Maximum BTU/hr the space can support)
=___________________ BTU/hr
BTU/hr (maximum the space can support)
BTU/hr (actual amount of Btu/Hr used)
"
of the
BTU/hr
BTU/hr
BTU/hr
Example:
BTU/hr
Gas water heater
BTU/hr
Vent-free heater +
BTU/hr
Total
Figure 2 - Ventilation Air Inside Building
8
30,000
BTU/hr
26,000
BTU/hr
=
56,000
BTU/hr
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