Installation Guide

Page 5
AIR FOR
COMBUSTION AND
VENTILATION
Continued
DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Determining if You Have A Unusually Tight Construction or Unconfined Space
Use this work sheet to determine if you have a unusually tight construction 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 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. = 51,200 (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 Example:
Vented gas heater ________________ Btu/Hr Gas water heater 40,000 Btu/Hr
Gas fireplace logs ________________ Btu/Hr Vent-free heater + 30,000 Btu/Hr
Other gas appliances* + ________________ Btu/Hr Total = 70,000 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: 51,200 Btu/Hr (maximum the space can support)
70,000 Btu/Hr (actual amount of Btu/Hr used)
The space in the above example is a unusually tight construction 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 5.
B. Vent room directly to the outdoors. See Ventilation Air From Outdoors, page 5.
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 my be operated does not meet the required volume for indoor
combustion air, combustion and ventilation airs hall be provided by one of the methods described in the
National Fuel Gas Code, ANSI Z223.1/NFPA 54, the International Fuel Gas Code or applicable local
codes.”