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The opening shall c ommence
within 12in. (300 ram) of the
ceiling. Appliances
inthe space shall have c learances
ofatleast 1
in.(25 ram) f rom the sides a nd back a nd 6in.(150 ram) f rom the
front. The opening shall directly communicate
with the outdoors
or
shall c onmmnicate
through a vertical or horizontal duct t othe
outdoors
orspaces
(crawl orattic) that f reely communicate
with the
outdoors.
IndoorCombustion Air© NFPA & AGA
Standard a ndKnown-Air-Infiltration RateMethods
Indoor airispermitted
forcombustion,
ventilation,
and dilution, if
the Standard orKnown-Air-Infiltration
Method isused.
CARBON MONOXIDE POISONING
HAZARD
Failure t ofollow this warning could r esult inpersonal
iniury ordeath.
Many homes require airtobesupplied from outdoors
forfurnace combustion,
ventilation,
and dilution o fflue
gases.
The furnace combustion
airsupply nmst beprovided in
accordance
with this instruction
manual.
Standard
Method
1. The space has no less volume
than 50 cubic feet per 1,000
Btuh
of the maximum
input
ratings
for all gas appliances
installed
in the space and
2. The air infiltration
rate is not known
to be less than 0.40 air
changes
per hour (ACH).
The Known
Air Infiltration
Rate Method
shall be used,
if the
infiltration
rate is known
to be:
1. Less than 0.40 ACH and
2. Equal to or greater
than 0.10 ACH
Infiltration
rates greater
than 0.60
ACH
shall not be used.
The
minimum
required
volume
of the space varies with the number
of
ACH and shall be determined
per Table 4 or Equations
1 and 2.
Deternfine
the minimum
required
volume
for each appliance
in the
space
and
add the volumes
together
to get the
total nfininmm
required
volume
for the space.
Table 4 - Minimum
Space Volumes
were deternfined
by using the
following
equations
from the current
edition
of the National
Fuel
Gas Code ANSI Z223.I/NFPA
54, 9.3.2.2:
1. For
other
than
fan-assisted
appliances,
such
as a draft
hood-equipped
water heater:
Volume
_ 21ft3
_ " -
!other
__
Other ACH _000 Btu/hrJ
A04002
2. For fan-assisted
appliances
such as this furnace:
Volume
_ 15ft 3 f"
I _
"_
Fae
ACH
_000" Btu/hrJ
A04003
If: Iother = combined
input of all other than fan-assisted
appliances
in Btuh/hr
Ifan = combined
input of all fan-assisted
appliances
in Btuh/hr
ACH = air changes
per hour (ACH shall not exceed
0.60.)
The following
requirements
apply
to the Standard
Method
and to
the Known
Air Infiltration
Rate Method.
1. Adjoining
rooms can be considered
part of a space if:
a. There
are no closeable
doors between
rooms.
b. Combining
spaces on same floor level. Each opening
shall
have free area of at least 1 in.2/1,000
Btuh (2,000 mm2/kW)
of the total input rating of all gas appliances
in the space,
but not less than 100 in. 2 (0.06
m2). One opening
shall
commence
within
12 in. (300 ram) of the ceiling
and the
second
opening
shall commence
within
12 in. (300 ram)
of the floor. The minimum
dimension
of air openings
shall
be at least 3 in. (80 ram).
See Fig. 7.
c. Combining
space on different floor levels. The volumes
of
spaces on different floor levels shall be considered
as com-
municating
spaces if connected
by one or more permanent
openings
in doors
or floors having
free area of at least 2
in.2/1,000
Btuh (4,400
mm2/kW)
of total input rating
of
all gas appliances.
2. An attic or crawlspace
may be considered
a space that freely
conmmnicates
with
the
outdoors
provided
there
are ad-
equate
permanent
ventilation
openings
directly
to outdoors
having
free area of at least 1-in.2/4,000
Btuh
of total input
rating for all gas appliances
in the space.
3. In spaces that use the Indoor
Combustion
Air Method,
in-
filtration
should
be adequate
to provide
air for combustion,
permanent
ventilation
and dilution
of flue gases. However,
in buildings
with unusually
tight construction,
additional
air
MUST
be provided
using
the methods
described
in the
Outdoor
Combustion
Air Method
section.
4. Unusually
tight
construction
is defined
as Construction
with:
a. Walls and ceilings
exposed to the outdoors
have a continu-
ous, sealed vapor barrier. Openings
are gasketed
or sealed
and
b. Doors
and openable
windows
are weatherstripped
and
c. Other openings
are caulked or sealed. These include
joints
around window
and door frames, between
sole plates and
floors,
between
wall-ceiling
joints,
between
wall panels,
at penetrations
for plumbing,
electrical
and gas lines, etc.
Combination
of Indoor
and
Outdoor
Air
1. Indoor
openings
shall comply
with
the Indoor
Combus-
tion Air Method
below
and,
2. Outdoor
openings
shall be located
as required
in the Out-
door Combustion
Air Method
mentioned
previously
and,
3. Outdoor
openings
shall be sized as follows:
a. Calculate
the Ratio of all Indoor Space volume
divided
by
required
volume
for Indoor
Combustion
Air Method be-
low.
b. Outdoor
opening
size reduction
Factor
is I nfinus the Ra-
tio in a. above.
c. Minimum
size of Outdoor
openings
shall be the size re-
quired in Outdoor
Combustion
Air Method
above multi-
plied by reduction
Factor
in b. above. The minimum
di-
mension
of air openings
shall be not less than 3 in. (80 ram).
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