Canadian installations must be in accordance with NSCNGPIC
and all authorities having jurisdiction.
Air for combustion must not be contaminated by halogen
compounds which include fluoride, chloride, bromide, and
iodide. These elements are found in aerosol sprays, deter-
gents, bleaches, cleaning solvents, salts, air fresheners, and
other household products.
The operation of exhaust fans, kitchen ventilation fans,
clothes dryers, or fireplaces could create a negative air
pressure condition at the furnace. Make-up air must be
provided for these devices, in addition to that required by the
furnace.
All fuel-burning equipment must be supplied with air for combus-
tion of the fuel. Sufficient air MUST be provided to ensure there
will not be a negative pressure in the equipment room or space. In
addition, a positive seal MUST be made between the furnace
cabinet and the return-air duct to avoid pulling air from the burner
area and draft safeguard opening into the circulating air.
The requirements for combustion and ventilation air depend upon
whether the furnace is located in a CONFINED or UNCONFINED
space.
UNCONFINED SPACE
An unconfined space must have at least 50 cu ft for each 1000
Btuh of input for all the appliances (such as furnaces, clothes
dryer, water heaters, etc.) in the space.
For Example:
58TMA FURNACE
HIGH-FIRE INPUT
BTUH
MINIMUM SQ FT
WITH
7-1/2 FT CEILING
63,000
420
84,000
560
105,000
700
123,000
820
If the unconfined space is constructed unusually tight, air for
combustion and ventilation MUST come from either the outdoors
or spaces freely communicating with the outdoors. Combustion
and ventilation openings must be sized the same as for a confined
space as defined below. Return air must not be taken from the
room unless an equal or greater amount of air is supplied to the
room.
CONFINED SPACE
A confined space is defined as a space whose volume is less than
50 cu ft per 1000 Btuh of the total input ratings of all appliances
installed in that space. A confined space MUST have 2 permanent
openings, 1 within 12 in. of the ceiling, and the other within 12 in.
of the floor which freely communicate with an unconfined space or
the outdoors. (See Fig. 2.)
Fig. 2—Confined Space: Air for Combustion and
Ventilation from an Unconfined Space
A93387
RETURN
AIR
6
″
MIN
(FRONT)
†
SUPPLY AIR
VENT THROUGH ROOF
(CATEGORY I)
1 SQ IN.
PER 1000
BTUH* IN DOOR
OR WALL
12
″
MAX
1 SQ IN.
PER 1000
BTUH* IN DOOR
OR WALL
12
″
MAX
INTERIOR
HEATED
SPACE
* Minimum opening size is 100 square in. with
minimum dimensions of 3-In.
†
Minimum of 3-In. when type B-1 vent is used.
UNCONFINED
SPACE
Fig. 3—Confined Space: Air for Combustion and
Ventilation from Outdoors
A93388
DUCTS TO
OUTDOORS
1 SQ IN.
PER 4000
BTUH
*
RETURN
AIR
VENT
THROUGH
ROOF
(CATEGORY I)
D
B
A
C
E
1 SQ IN.
PER 4000
BTUH
DUCT
TO
OUTDOORS
SUPPLY AIR
1 SQ IN.
PER 2000
BTUH*
DUCTS
TO
OUTSIDE
12
″
MAX
12
″
MAX
CONFINED
SPACE
12
″
MAX
12
″
MAX
1 SQ IN.
PER 4000
BTUH
*
OUTDOORS
1 SQ IN.
PER 4000
BTUH
*
1 SQ IN.
PER 2000
BTUH*
12
″
MAX
Use any of the following
combinations of openings:
A & B C & D D & E F & G
NOTE:
*Minimum dimensions of 3-In.
F
G
4
