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DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Determining if You Have a Conned or Unconned Space
Use this worksheet to determine if you have a conned or unconned 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 20 ft. (length) × 16 ft. (width)×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)
3. Add the BTU/hr of all fuel burning appliances in the space.
*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)
56,000 BTU/hr (actual amount of BTU/hr used)
The space in the above example is a conned 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:
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 ”
on next page.
Vent room directly to the outdoors. See “ Ventilation Air From Outdoors ” on next page.
c) Install a lower BTU/hr heater if lower BTU/hr size makes room unconned. If the actual BTU/hr used is less
than the maximum BTU/hr the space can support, the space is an unconned space. You will need no
additional fresh air ventilation.
a)
b)
Example:
Gas water heater 30,000 BTU/hr
Vent-free heater + 26,000 BTU/hr
Total = 56,000 BTU/hr
BTU/hr
BTU/hr
BTU/hr
BTU/hr
BTU/hr
BTU/hr
BTU/hr
Vent-free heater
Gas water heater*
Gas furnace
Vented gas heater
Gas heater logs
Other gas appliances* +
Total =