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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.
3. Add the Btu/Hr of all fuel burning appliances in the space.
Vent-free heater Btu/Hr
Gas water heater* Btu/Hr
Gas furnace Btu/Hr
Vented gas heater Btu/Hr
Gas heater logs Btu/Hr
Other gas appliances* + Btu/Hr
Total = Btu/Hr
*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 the space can support with the actual amount of Btu/Hr used.
Btu/Hr (maximum the space can support)
Btu/Hr (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 Inside Building.
B. Vent room directly to the outdoors. See Ventilation Air From Outdoors .
C. Install a lower Btu/Hr heater, if lower Btu/Hr size makes room unconfined.
Figure 2 -Ventilation Air from Inside Building
Example:
Gas water heater 30,000 Btu/Hr
Vent-free heater + 26,000 Btu/Hr
Total = 56,000 Btu/Hr
NOTE: 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, Section 5.3 or applicable local codes.
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" of the 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, Section 5.3, Air for Com-
bustion and Ventilation for required size of ventilation grills
or ducts.
Ventilation Air From lnside Building
Ventilation Air From Outdoors
Provide extra fresh air by using ventilation grills or ducts.
You must provide two permanent openings: one within
12" of the ceiling and one within 12" of the floor. Connect
these items directly to the outdoors or spaces open to
the outdoors. These spaces include attics and crawl
spaces. Follow the National Fuel Gas Code, NFPA 54/
ANSI Z223.1, Section 5.3, Air for Combustion and Ven-
tilation for required size of ventilation grills or ducts.
IMPORTANT: Do not provide openings for inlet or outlet
air into attic if attic has a thermostat-controlled power
vent. Heated air entering the attic will activate the power
vent.
Rework worksheet, adding the space of the adjoining
unconfined space. The combined spaces must have
enough fresh air to supply all appliances in both spaces.
Figure 3 -Ventilation Air from Outdoors