Manual 2100-579A
Page 30 of 41
APPLIANCES LOCATED IN CONFINED SPACES
In unconfined spaces in buildings, infiltration may be
adequate to provide air for combustion, ventilation,
and dilution of flue gases. However, in buildings of
unusually tight construction, additional air shall be
provided using the method described under “All Air
From Outdoors” in Figure 14.
An unconfined space (such as an open basement) must
have a minimum volume of 50 cubic feet per 1,000
BTUH of total of
all
appliances in area. Adjoining
rooms may be counted as one area only if there are not
doors between the rooms.
Shown in Table 8 are the required minimum areas
in square feet to qualify as an unconfined space for
various total BTUH input ratings. The table is based
on a room(s) with 8 foot ceiling heights.
If the unconfined space is within a building having
insufficient air because of tight construction, the air
for combustion and ventilation shall be obtained from
outdoors or from spaces freely communicating with the
outdoors. Under these conditions a permanent opening
or openings have a total free area of not less than one
square inch per 5,000 BTU per hour (28 square inches
per hour ) of total input rating of all appliances shall be
provided. For combustion air options see “Combustion
Air Requirements”.
NOTE: Each opening shall have a free area of not
less than one square inch per 1,000 BTU per
hour (140 square inches per gallon per hour)
of the total input rating of all appliances in
the enclosure.
FIGURE 13
APPLIANCES LOCATED
IN CONFINED SPACES
ALL AIR FROM INSIDE THE BUILDING
ALL AIR FROM INSIDE BUILDING
The confined space shall be provided with two
permanent openings, one near the top of the enclosure
and one near the bottom. Each opening shall have a
free area of not less than one square inch per 1,000
BTU per hour (140 square inches per gallon per
hour) of the total input rating of all appliances in the
enclosure freely communicating with interior areas
having in turn adequate infiltration from the outside.
(See Figure 13.) Also see Table 9 on the following
page for specific ventilation opening requirements for
the furnace only.
The flow of combustion and ventilating air must not
be obstructed from reaching the furnace.
TABLE 8
SQUARE FEET REQUIRED TO
QUALIFY AS UNCONFINED SPACE
Total
BTUH
Input
Unconfined Space
Minimum Area in
Square Feet
8' Ceiling Height
60,000
80,000
375
500
85,000
105,000
531
656
115,000
120,000
719
750
140,000
145,000
875
906
160,000
200,000
1000
1250
