Combustion air must be free of acid
forming chemicals; such as sulphur, flu-
orine and chlorine. These elements are
found in aerosol sprays, detergents,
bleaches, cleaning solvents, air fresh-
eners, paint and varnish removers,
refrigerants and many other commercial
and household products. Vapors from
these products when burned in a gas
flame form acid compounds. The acid
compounds increase the dew point
temperature of the flue products and
are highly corrosive after they con-
dense.
ALL FURNACE INSTALLATIONS
MUST COMPLY WITH THE NATIONAL
FUEL GAS CODE AND LOCAL
CODES TO PROVIDE ADEQUATE
COMBUSTION AND VENTILATION
AIR FOR THE FURNACE. FAILURE
TO DO SO CAN CREATE HAZ-
ARDOUS CONDITIONS RESULTING
IN PROPERTY DAMAGE, BODILY
INJURY OR DEATH FROM SMOKE,
FIRE OR CARBON MONOXIDE.
Combustion air requirements are deter-
mined by whether the furnace is in an
open (unconfined) area or in a confined
space such as a closet or small room.
See Figures 7 and 8.
EXAMPLE 1.
FURNACE LOCATED IN AN UNCON-
FINED SPACE
Using indoor air for combustion.
An unconfined space must have at
least 50 cubic feet for each 1,000
BTUH of the total input for all appli
-
ances
in the space. Here are a few
examples of the room sizes required for
different inputs. The sizes are based on
8 foot ceilings.
BTUH Minimum Sq. Feet Typical Room Size
Input With 8' Ceiling With 8' Ceiling
50,000 312 14*x24* or 18*x18*
75,000 469 15*x31* or 20*x24*
100,000 625 20*x31* or 25*x25*
125,000 833 23*x34* or 26*x30*
If the open space containing the fur-
nace is in a building with tight construc-
tion (contemporary construction), out-
side air may still be required for the fur-
nace to operate and vent properly.
Outside air openings should be sized
the same as for a confined space.
FIGURE 8
AIR FROM ATTIC/CRAWL SPACE
EXAMPLE 2.
FURNACE LOCATED IN A CONFINED
SPACE
A confined space (any space smaller
than shown above as “unconfined”)
must have openings into the space
which are located in accordance with
the requirements set forth in the follow-
ing subsections A and B. Size the open-
ings by how they are connected to the
heated area or to the outside, and by
the input of all appliances in the space.
If confined space is within a building
with tight construction, combustion air
must be taken from outdoors or area
freely communicating with the outdoors.
A. USING INDOOR AIR FOR COM-
BUSTION, ALL OF THE MODELS
IMPORTANT: Air should not be taken
from a heated space with a fireplace,
exhaust fan or other device that may
produce a negative pressure.
If combustion air is taken from the heat-
ed area, the openings must each
have at least 100 square inches of
free area. Each opening must have
at least one square inch of free area
for each 1,000 Btuh of total input in
the space. Here are some examples
of typical openings required.
Btuh Free Area
Input Each Opening
100,000 100 Square Inches
AIR INTAKE PIPE CONNECTION
(RGPE UPFLOW/HORIZONTAL
ONLY)
A double-elbow may be installed
to top inlet air opening, BUT IS
NOT REQUIRED.This will help to
prevent accidental blockage of
the intake opening. Reference
Figure 9 for proper elbow diame-
ter.
NOTE: Inlet is specifically designed
to prevent material from being pulled
into furnace. If elbows are not used,
the intake opening must be kept
clean and free of debris.
It is also acceptable to run the
condensate drain (or refrigerant)
line access over the air intake
hole as long as a 1" minimum
clearance is maintained.
B. USING OUTDOOR AIR FOR
COMBUSTION, ALL OF THE
MODELS
IMPORTANT: Never take com-
bustion air from an attic space
that is equipped with power
ventilation.
The confined space must com-
municate with the outdoors
according to Methods 1 and 2.
The minimum air opening dimen-
sion shall not be less than 3 inch-
es. When using ducts, they shall
be of the same cross-sectional
area as the free area of the open-
ings to which they connect.
WARNING
!
13
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