OWNER'S OPERATION AND INSTALLATION MANUAL VENT-FREE HEARTH HEATER BTU/Hr
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FRESH AIR FOR COMBUSTION AND VENTILATION
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 conned or unconned space.
Space: Includes the room in which you will install heater plus any adjoining rooms with doorless passageways or ventila-
tion 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 20 ft. (length) x 16 ft. (width) x 8 ft. (ceiling height) = 2560 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.
_____________________(volume of space) ¸ 50 cu. ft. = (Maximum Btu/Hr the space can support)
Example: 2560 cu. ft. (volume of space)¸ 50 cu. ft. = 51.2 x 1000 = 51,200 (maximum Btu/Hr the space can support)
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 replace 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 out-doors.
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)
60,000 Btu/Hr (actual amount of Btu/Hr used)
The space in the above example is a conned 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 unconned space, remove
door to adjoining room or add ventilation grills between rooms. See “Ventilation Air From Outdoors,” page 10.
B. Vent room directly to the outdoors. See “Ventilation Air From Outdoors,” page 10.
C. Install a lower Btu/Hr heater, if lower Btu/Hr size makes room unconned.
If the actual Btu/Hr used is less than the maximum Btu/Hr the space can support, the space is an unconned space. You will
need no additional fresh air ventilation.
Example:
Gas water heater 30,000 Btu/Hr
Vent-free heater + 30,000 Btu/Hr
Total = 60,000 Btu/Hr
If the area in which the heater may be operated is smaller than that defined as an
unconfined space or if 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, Section 5.3 or applicable local codes.
WARNING