8
103296
DETERMINING 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 size
22 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.
Vent-free firebox
___________________ Btu/Hr
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
Example:
Gas water heater
40,000
Btu/Hr
Vent-free firebox with log heater
+
39,000
Btu/Hr
Total
=
79,000
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 work sheet, adding the space of an adjoining room. If the extra space pro-
vides an unconfined space, remove door to adjoining room or add ventilation grills
between rooms. See Ventilation Air from Inside Building, page 9.
B. Vent room directly to the outdoors. See Ventilation Air from Outdoors, page 9.
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.
WARNING ICON
G 001
WARNING
If the area in which the firebox and gas log heater may be oper-
ated is smaller than that defined as an unconfined space, provide
adequate combustion and ventilation air by one of the methods
described in the
National Fuel Gas Code, ANSI Z223.1, 1992,
Section 5.3.
AIR FOR
COMBUSTION
AND
VENTILATION
Continued
