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8

Use this work sheet 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 

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 22 ft. (length) x 18 ft. 

(width) x 8 ft. (ceiling height) = 3168 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 20 to determine 

the maximum Btu/Hr the space can sup-

port.

 

 ________ (volume of space) x 20 = (Maxi-

mum Btu/Hr the space can support)

 

Example: 3168 cu. ft. (volume of space) x 20 

= 63,360 (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

 

* Do not include direct-vent gas appliances. 

Direct-vent draws combustion air from the 

outdoors and vents to the outdoors.

 

 

Gas water heater 

 _________ Btu/Hr

 

Vent-free fireplace 

+ ________ Btu/Hr

 Total 

= ________ Btu/Hr

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:  63,360  Btu/Hr  (maximum  the 

space can support) 

 

 

79,000 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 sup-

port. 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 9.

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.

the International Fuel Gas Code, 

  40,000
  39,000
  79,000