4
OWNER
MANUAL
AIR FOR
COMBUSTION AND
VENTILATION
Continued
DETERMINING FRESH-AIR FLOW FOR FIREBOX LOCATION
Determining if You Have a Confined or Unconfined Location
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 odorless 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) divide by 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
EXAMPLE:
Vented gas heater
__________________ Btu/Hr
Gas water heater 40,000 Btu/Hr
Gas firebox heater
__________________ Btu/Hr
Gas firebox
Other gas appliances*
+ ________________ Btu/Hr
Logs
+ 39,000 Btu/Hr
Total
= ________________ Btu/Hr
Total
= 79,000 Btu/Hr
*Do not include the 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 of Btu-Hr 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 that 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 provides an unconfined space, remove the
door to adjoining room or add ventilation grills between rooms. See
Ventilation Air from Inside Building
, page 5.
B. Vent room directly to the outdoors. See
Ventilation Air from Outdoo
rs, page 5.
C. Install a lower Btu/Hr gas log heater, if lower Btu/Hr size makes room unconfined.
If the actual Btu/Hr used is less that 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 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 constructions, 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.
