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20. The National Fuel Gas Code defines a confined
space as a space whose volume is less than 50
ft
3
per 1,000 Btu/hr (4.8 m
3
/kw) of the aggregate
input rating of all appliances installed in that
space and an unconfined space as a space
whose volume is not less than 50 ft
3
per 1,000
Btu/hr (4.8 m
3
/kw) of the aggregate input rating
of all appliances installed in that space. Rooms
communicating directly with the space in which
the appliances are installed, through openings
not furnished with doors, are considered a part
of the space.
21.
WARNING:
If the area in which the
heater may be operated is smaller than that
defined as an unconfined space,or if the building
is of unusually tight construction, provide
adequate combustion and ventilation air by one
of the methods described in the National Fuel
Gas Code, ANSI Z223.1/NFPA 54, Section
5.3 or applicable local codes.
The purpose of this worksheet is to help you determine if you are planning to install this heater in an “unconfined”
or a “confined” space. An “unconfined” space is one that is large enough to meet all the combustion and
ventilation air requirements of all the fuel burning appliances to be in operation in this space. No additional
air requirements are needed. A “confined” space is one that
is not
large enough to meet the combustion
and ventilation air requirements for all the fuel burning appliances in that space. As a result, additional air
is required in this space to meet the appliance needs. Check with your installer on ways to accomplish this,
or use a smaller Btu/hr input heater.
STEP 1:
Determine the volume of the space in which the heater is to be installed. Include adjoining
rooms with doorless passageways. Example: 24' (long) x 16' (wide) x 8' (high) = 3072 ft
3
.
L E N GT H x W I DT H x H E I G H T = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ F t
3
STEP 2:
Multiply the volume of the space (calculated in Step 1) by 20 BTU/hr to determine the
maximum BTU/hr that the space can support without additional combustion and ventilation
air provided.
Result from Step 1 ____________________ x 20 BTU/hr = ____________________ BTU/hr
STEP 3:
Add the BTU/hr inputs of all
fuel burning
appliances in this space.
NOTE: DO NOT include
Direct-Vent gas appliances because these have sealed combustion systems that draw
combustion air from outdoors.
Examples of appliances to consider include: gas ranges,
gas water heaters, gas logs, kerosene heaters, etc.
Proposed Vent-Free Heater
______________________________ BTU/hr
Fuel Burning Appliance #1
______________________________ BTU/hr
Fuel Burning Appliance #2
______________________________ BTU/hr
TOTAL
______________________________ BTU/hr
STEP 4:
Compare the results from Step 2 and Step 3.
If the result from Step 2 is
greater
than the result from Step 3, the area where the heater is to be installed
can be classified as an “unconfined space.” This means that the space is capable of handling the combustion
and ventilation air requirements of the existing fuel burning appliance(s) and the proposed heater.
If the result from Step 2 is
less
than the result from Step 3, the area where the heater is to be installed is
classified as a “confined space.”
This means that either additional combustion and ventilation air must
be provided into this space (use the methods described in the National Fuel Gas Code, ANSI Z223.1-
latest edition) or the size of the proposed heater must be reduced so that the above calculations show
the space to be an unconfined space.
