www.desatech.com
123721-01E
7
air For ComBUsTioN aNd VeNTilaTioN
Continued
Example:
Space size 16 ft. (length) x 14 ft.
(width) x 8 ft. (ceiling height) = 1792 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 support.
________ (volume of space) x 20 = (Maxi
-
mum Btu/Hr the space can support)
Example:
1792 cu. ft. (volume of space) x
20 = 35,840 (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.
Example:
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 space can support)
______ Btu/Hr (actual amount used)
Example:
35,840 Btu/Hr (maximum the
space can support)
56,000 Btu/Hr (actual amount of
Btu/Hr used)
The space in the previous 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 adjoin
-
ing room or add ventilation grills between
rooms. See
Ventilation Air From Inside
Building.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors
, page 8
.
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 maxi
-
mum Btu/Hr the space can support,
the space is
an unconfined space. You will need no additional
fresh air ventilation.
WARNING: If the area in which
the heater may be operated does
not meet the required volume for
indoor combustion air, combus-
tion and ventilation air shall be
provided by one of the methods
described in the
National Fuel
Gas Code, ANSI Z223.1/NFPA 54,
the
International Fuel Gas Code,
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" of the
ceiling and one within 12" of the floor 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, Air for Combustion and
Ventilation
for required size of ventilation
grills or ducts.
30,000
+ 26,000
= 56,000
Figure 2 - Ventilation Air from Inside
Building
Or
Remove
Door into
Adjoining
Room,
Option
3
Ventilation Grills
Into Adjoining Room,
Option 2
Ventilation
Grills Into
Adjoining
Room,
Option 1
12"
12"
