AIR FOR COMBUSTION
AND VENTIlATION
Continued
DETERMINING FRESH-AIR FLOW
FOR HEATER LOCATION
Determining if you Have a Confi ned or
Unconfi ned Space
Use this work sheet to determine if you have
a confi ned or unconfi ned 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 20 ft. (6.1 m) (length)
x 16 ft. (4.88 m) (width) x 8 ft. ( .44 m)
(ceiling height) = 560 cu. ft. (7 .49 m3)
(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 support.
________ (volume of space) x 20 = (Maxi-
mum Btu/Hr the space can support)
Example: 560 cu. ft. (72.49 m3) (volume of
space) x 20 = 51,200 (maximum Btu/Hr the
space can support)
3. Add the Btu/Hr of all fuel burning appliances
in the space.
Vent-free heater ____________Btu/Hr
Gas water heater* ____________Btu/Hr
Gas furnace ____________Btu/Hr
Vented gas heater ___________ Btu/Hr
Gas fi replace logs ____________Btu/Hr
Other gas appl ___________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.
Example:
Gas water heater ___40,000____Btu/Hr
Vent-free heater + ___20,000____Btu/Hr
Total = ___60,000____ Btu/Hr
4. Compare the maximum Btu/Hr the space can
support with the actual amount of Btu/Hr used.
_______ Btu/Hr (maximum can support)
_______ Btu/Hr (actual amount)Example:
51,200 Btu/Hr (maximum the
space can support)
60,000 Btu/Hr (actual amount of
Btu/Hr used)
The space in the above example is a confi ned
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 unconfi ned space, remove door to
adjoining room or add ventilation grills
between rooms. See Ventilation Air From
Inside Building, page 7.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors, page 7.
C. Install a lower Btu/Hr heater, if lower Btu/Hr
size makes room unconfi ned.
If the actual Btu/Hr used is less than the maxi-
mum Btu/Hr the space can support, the space
is an unconfined space. You will need no
additional fresh air ventilation.
6
WARNING: If the area in which
the heater may be operated is small-
er than that defi ned as an unconfi ned
space or if the building is of unusua-
lly tight construction, provide adequ-
ate 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.
VENTILATION AIR
Ventilation Air From Inside Building. This fresh
air would come from an adjoining unconfined
space. When ventilating to an adjoining
unconfined space, you must provide two
permanent openings: one within 12" (30.5
cm) of the ceiling and one within 12" (30.5 cm)
of the fl oor on the wall connecting the two
spaces (see options 1 and 2, Figure 2). You
can also remove door into adjoining room (see
option 3, Figure 2). Follow the National Fuel
Gas Code, ANSI Z223.1/NFPA 54, Section
5.3, Air for Combustion and Ventilation for
required size of ventilation grills or ducts.
