W415-0809 / A / 05.10.10
In this example, because there is no door to the adjoining room, the volume of the adjoining room may be
added to the volume of the room with the heater to get a total unconﬁ ned space.
The total unconﬁ ned space: 800 + 1200 = 2000 cubic feet.
Maximum BTU/h: 2000x1000 = 40,000 BTU/h
If in this example a solid door separates Room 1 from Room 2, the volume of Room 2 could not be used. In
this case the maximum BTU/h would be:
Maximum BTU/h: 800x1000 = 16,000 BTU/h
If there are no more fuel burning appliances within this space then the 40,000 BTU/h input of the appliance is
suitable to be installed. This also assumes that the construction of this space is not unusually tight.
This would be considered a conﬁ ned space since it can not support the 40,000 BTU/h input of the appliance
and it would be necessary to provide adequate combustion and ventilation air to Room 1.
Unusually tight construction is deﬁ ned as construction where:
A) Walls and ceilings exposed to the outside atmosphere have a continuous water vapour retarder with a
rating of 1 perm (6 x 10-11 kg per pa-sec-m2) or less with openings gasketed or sealed, and
B) Weather stripping has been added on openable windows and doors, and
C) Caulking or sealants are applied to areas such as joints around window and door frames, between sole
plates and ﬂ oors, between wall-ceiling joints, between wall panels, at penetrations for plumbing, electrical,
and gas lines, and at other openings.
n unvented room appliance is recommended for use as a secondary heat source rather than as a primary
source. Gas combustion produces water vapour which could occur at the rate of approximately one ounce of
water for every 1,000 BTU/hr of gas input. During the cold weather season, indoor humidity levels tend to be
low. Consequently, this water vapour can enhance the living space. However if a problem should occur:
A) Ensure sufﬁ cient combustion and circulation air
B) Use a dehumidiﬁ er
C) Do not use the unvented room appliance as a primary heat source
Without sufﬁ cient fresh air for proper operation, poor fuel combustion can result. Carbon Monoxide is a result
of poor combustion.
If additional fresh air is required, use one of the methods described in the National Fuel
Gas Code, ANSI Z223.1, Section 5.3 or the applicable local code.
Room Volume = Length x Width x Height
Max BTU/hr = Room Volume x 1000 / 50
If for example:
The length of the rooms is 10 feet,
The width of Room 1 is 10 feet,
The width of Room 2 is 15 feet,
The height of the rooms is 8 feet.
The volume of Room 1: 10x10x8 = 800 cubic feet
The volume of Room 2: 10x15x8 = 1200 cubic feet