6
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 confined 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×Width×Height= cu.ft. (volume of space)
Example:
Space size 20ft. (length)×16ft.(width)×8ft. (ceiling height)=2560cu. 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)
3. Add the Btu/Hr of all fuel burning appliances in the space.
Vent-free heater
Gas water heater*
Gas furnace
Vented gas heater
Gas heater logs
Other gas appliances* +
Total =
*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)
71,000 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, re
-
move door to adjoining room or add ventilation grills between rooms. See “Ventilation Air From Outdoors”
,
page
7.
b)
Vent room directly to the outdoors. See “Ventilation Air From Outdoors”, page 7.
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 may be operated does not meet the required volume for indoor
combustion air, combustion and ventilation air shall 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.
Example:
Gas water heater 40,000 Btu/Hr
Vent-free heater + 31,500 Btu/Hr
Total = 71,500 Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
Btu/Hr
