Vanguard Heating VMH10TN - Manual (Page 7)

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AIR FOR
COMBUSTION
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VENTILATION
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DETERMINING FRESH-AIR FLOW FOR FIREPLACE 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 fireplace 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 16 ft. (length) x 14 ft. (width) x 8 ft. (ceiling height) =
1792 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. Multiply the space volume by 1000 Btu/Hr per 50 cubic feet to determine the maximum
Btu/Hr the space can support.
______________ (volume of space) x 1000 Btu/Hr = (Maximum Btu/Hr the space can support)
50 Cubic Feet
Example: 1792 Cubic Feet (volume of space) x 1000 Btu/Hr = 35,840 Btu/Hr
50 Cubic Feet
This is the maximum Btu/Hr the space can support.
3. Add the Btu/Hr of all fuel burning appliances in the space.
Vent-free fireplace ___________________ Btu/Hr
Gas water heater* ___________________ Btu/Hr
Gas furnace ___________________ Btu/Hr
Vented gas heater ___________________ Btu/Hr
Gas fireplace logs ___________________ Btu/Hr
Other gas appliances* + ___________________ Btu/Hr
Total = ___________________ Btu/Hr
Example: Gas water heater 30,000 Btu/Hr
Vent-free fireplace + 10,000 Btu/Hr
Total = 40,000 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: 35,840 Btu/Hr (maximum the space can support)
40,000 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 8.
B. Vent room directly to the outdoors. See Ventilation Air From Outdoors, page 9.
C. Install a lower Btu/Hr fireplace, 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.
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