If the installation area meets the definition of
"Unconfined Space" and does not have additional air
requirements as described, the furnace may be installed
without making special provisions for combustion and
ventilation air.
Whenever this furnace is installed in an area along
with one or more gas appliances, the total Btu/hr
input of all appliances must be included when
determining the free area requirements for
combustion and ventilation air openings.
Do not block the combustion or ventilation air
openings in the furnace. Any blockage will result in
improper combustion and may result in a fire
hazard or unsafe condition.
If ventilation and/or combustion air must be supplied to the "Confined Space" from inside the building structure, two
permanent openings to an additional room of sufficient volume as to combine the volumes of the spaces to meet the
criteria for an "Unconfined Space" must be created. Each opening must have a free area of not less than one square
inch per 1000 Btu per hour of total input of all appliances within the "Confined Space" (but not less than 100 square
inches). These openings must be located 12 inches from the top and bottom of the furnace area respectively and must
be at least 3 inches long on the smaller side of the opening (See Figure 2). Neither opening can be blocked at any time.
Figure 2
CONFINED SPACE / INDOOR AIR
TOTAL INPUT
(Btuh)
MIN. FREE AREA
(Sq. In.)
ROUND DUCT
(Dia. In.)
40,000
60,000
80,000
100,000
120,000
140,000
160,000
100
100
100
100
120
140
160
12
12
12
12
13
14
15
EXAMPLE:
50,000 Btuh Furnace & 10,000 Btuh Water
Heater = 60,000 Btuh Total Input = 12"
Dia. Round Duct.
If ventilation and/or combustion air must be supplied to the "Confined Space" from outside the building structure,
two permanent openings to the outdoors must be created. Each opening must have a free area of not less than one
square inch per 4000 Btu per hour of total input of all appliances within the "Confined Space". These openings must
be located 12 inches from the top and bottom of the furnace area respectively (See Figures 3, 4, and 5). Neither
opening can be blocked at any time.
Figure 3
CONFINED SPACE / OUTDOOR AIR
TOTAL INPUT
(Btuh)
MIN. FREE AREA
(Sq. In.)
ROUND DUCT
(Dia. In.)
40,000
60,000
80,000
100,000
120,000
140,000
160,000
10
15
20
25
30
35
40
4
5
5
6
6
7
8
EXAMPLE:
50,000 Btuh Furnace & 10,000 Btuh Water
Heater = 60,000 Btuh Total Input = 5" Dia.
Round Duct.
20571201
Issue 0527
Page 9 of 28
