9
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
door-less 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 cu. ft. 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. = 51.2 or 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
Vented gas heater _______BTU/hr
Example:
Gas heater logs ________ BTU/hr
Gas water heater 30,000 BTU/hr
Other gas appl ___BTU/hr
Vent-free 26,000 BTU/hr
Total =________________ BTU/hr
Total
= 56,000 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 : 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 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, remove door to adjoining room or add ventilation
grills between rooms. See “Ventilation Air From Inside Building,” page 10.
b) Vent room directly to the outdoors. See “Ventilation Air From Outdoors”, page 10.
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.
