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COMBUSTION AND VENTILATION AIR
REQUIREMENT WORKSHEET
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
.
LENGTH x WIDTH x HEIGHT = ___________________________ Ft
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 then 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 one of 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.
