25783-5-1011
Page 7
Figure 1
WARNING
Rework worksheet, adding the space of the adjoining
unconfined space. The combined spaces must have enough
fresh air to supply all appliances in both spaces.
Ventilation Air From Outdoors
Provide extra fresh air by using ventilation grills or ducts. You must
provide two permanent openings: one within 12" of the ceiling and
one with 12" of the floor. Connect these items directly to the outdoors
or spaces open to the outdoors. These spaces include attics and
crawl spaces. In most cases for direct communication with the
outdoors or direct communication through a vertical duct a free
area opening of one square inch per 4,000 BTU/HR of heater input
rating for each grill. If a horizontal duct is used, a grill free area or
duct opening shall have a free area opening of one square inch per
2,000 BTU/HR for each grill. Follow the
National Fuel Code NFPA
54/ANSI Z223.1, Section 5.3 Air for Combustion and Ventilation
for
required size of ventilation grills or ducts.
IMPORTANT:
Do not provide openings for inlet or outlet air into attic
if attic has a thermostat-controlled power vent. Heated air entering
the attic will activate the power vent.
Figure 2
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 fireplace logs
BTU/Hr
Other gas appliances* +
BTU/Hr
Total
=
BTU/Hr
Example: Vented gas heater
20,000
BTU/Hr
Vent-free heater
+
18,000
BTU/Hr
Total
=
38,000
BTU/Hr
*Do not include direct-vent gas appliances. Direct vent draws
combustion air from the outdoors and vents to the outdoors.
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:
25,600
BTU/Hr (maximum the space can support)
38,000
BTU/Hr (actual amount of BTU/Hr used)
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, Section 5.3 or applicable local codes.
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 support. 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.
B. Vent room directly to the outdoors. See
Ventilation Air From
Outdoors.
C. Install a lower BTU/Hr heater, 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.
WARNING
You must provide additional ventilation air in a confined
space.
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 1). You can also remove door into adjoining room
(see option 3, Figure 1). Each ventilation grill or opening shall have
a minimum free area of one square inch per 1,000 BTU/HR of the
total input rating of the gas equipment in the confined space.
