7
Figure 2 - Ventilation Air
from Inside Building
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2. Divide the space volume by 50 cubic feet to determine the maximum Btu/Hr the space can support.
(volume of space)÷50 cu. ft.=(Maximum Btu/Hr the space can support).
3. 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 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:
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
.
Vent room directly to the outdoors. See
Ventilation Air From Outdoors
.
Install a lower Btu/Hr heater if lower Btu/Hr size makes room unconfined.
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, Air for Combustion and Ventilation, 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 inches of the ceiling and one within 12 inches
of the floor on the wall connecting the two spaces (see options 1 and 2, Figure 2). You can also remove the door
into the adjoining room (see option 3, Figure 2). Follow the
National Fuel Gas Code. NFPA 54/ANSI Z223.1,
Section 5.3, Air for Combustion and Ventilation
for required size of ventilation grills or ducts.
a)
b)
c)
Example:
Gas water heater 30,000 Btu/Hr
Vent-free heater + 26,000 Btu/Hr
Total = 56,000 Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Ventilation Air From Outdoors
Provide extra fresh air by using ventilation grills or ducts. You must provide
two permanent openings: one within 12 inches of the ceiling and one within
12 inches of the floor. Connect these items directly to the outdoors or spac
-
es 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 Ventilation
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 ad-
joining unconfined space. The combined spaces must have enough fresh
air to supply all appliances in both spaces.
