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AIR FOR
COMBUSTION AND
VENTILATION
Continued
DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Determining if You Have a Confined or Unconfined Space
Use this worksheet to determine if you have a confined or unconfined space.
Space: Includes the room in which you will install heater plus any adjoining rooms with doorless passageways or ventilation grills between
the rooms.
1.
Determine the volume of the space (length x width x height).
Length x Width x Height = ________________ cu. ft. (volume of space)
Example: Space size 18 ft. (length) x 16 ft. (width) x 8 ft. (ceiling height) = 2304 cu. ft. (volume of space)
If additional ventilation to adjoining room is supplied with grills or openings, add the volume of these rooms to the total volume of
the space.
2. Divide the space volume by 50 cubic feet to determine the maximum Btu/Hr the space can support.
_______________
Example: 2304 cu. ft. (volume of space) 50 cu. ft. = 46.1 or 46,100 (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 fireplace logs
Other gas appliances* + _________________ Btu/Hr
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: 46,100 Btu/Hr (maximum the space can support)
50,000 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 adjoin-
ing room or add ventilation grills between rooms. See Ventilation Air From Inside Building, page 6.
B. Vent room directly to the outdoors. See Ventilation Air From Outdoors, page 6.
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.
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, ANS Z223.1, Section 5.3 or applicable local codes.
104268
(volume of space) 50 cu. ft. = (Maximum Btu/Hr the space can support)
_________________ Btu/Hr
_________________ Btu/Hr
_________________ Btu/Hr
_________________ Btu/Hr
_________________ Btu/Hr
= _________________ Btu/Hr
OWNER'S MANUAL
Example:
Gas water heater
Vent-free heater
+
Total
=
5
40,000
Btu/Hr
10,000
Btu/Hr
50,000
Btu/Hr
Continued
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