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105509
OWNER’S MANUAL
DETERMINING FRESH-AIR FLOW FOR FIREBOX LOCATION
Determining if You Have a Confined or Unconfined Space
Use this work sheet to determine if you have a confined or unconfined space.
Space
: Includes the room in which you will install firebox 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 size22 ft. (length) x 18 ft. (width) x 8 ft. (ceiling height) = 3168 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:
3168 cu. ft. (volume of space)
÷
50 cu. ft. = 63.3 or 63,300 (maximum Btu/Hr the space can support)
3.
Add the Btu/Hr of all fuel burning appliances in the space.
Gas water heater*
_____________________ Btu/Hr
Gas furnace
_____________________ Btu/Hr
Vented gas heater
_____________________ Btu/Hr
Gas firebox 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:
63,300 Btu/Hr (maximum the space can support)
79,000 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, page 6.
B. Vent room directly to the outdoors. See Ventilation Air from Outdoors, page 6.
C. Install a lower Btu/Hr firebox, 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.
AIR FOR
COMBUSTION
AND VENTILATION
Continued
WARNING: If the area in which the firebox and gas log 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, 1992, Section 5.3 or
applicable local codes.
Continued
Example:
Gas water heater
40,000
Btu/Hr
Vent-free firebox
with log heater
+
39,000
Btu/Hr
Total
=
79,000
Btu/Hr
