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VENTILATION AND COMBUSTION AIR
WARNING
Air openings to combustion area must not be obstructed. By following the instructions below,
adequate combustion air can be maintained.
COMBUSTION AIR REQUIREMENTS
(MinimumOpening Requirement)
Outside Inside
Combustion
Air 1 Sq.
In./5000
BTU/Hour
(Step 4)
Combustion Air
1 Sq. In./1000
BTU/Hour (Min.
100 Sq. In.)
(Fig. 1)
Vertical
Ducts 1 Sq.
In./4000
BTU/Hour
(Fig. 2 & 3)
Horizontal
Ducts 1 Sq.
In./2000
BTU/Hour
(Fig. 4)
91,000 19 100 23 46
140,000 28 140 35 70
175,000 35 175 44 88
210,000 42 210 53 106
245,000 49 245 61 122
280,000 56 280 61 140
* A space whose volume is not less than 50 cubic feet per 1000 BTU/Hour of all
appliances installed in that space (cubic feet of space = height x width x length)
** A space whose volume is less than 50 cubic feet per 1000 BTU/Hour of all
appliances installed in that space (cubic feet of space = height x width x length)
BTU/Hr
Input
Unconfined Area* Confined Area**
Outside Combustion Air
1. Ventilation of boiler room must be adequate
enough to provide sufficient air to properly support
combustion and venting.
2.When theboileris locatedinan unconfinedspace
in a building of conventional construction frame,
masonryormetal,infiltrationnormallyisadequateto
provideairforcombustionandventilation.However,
in any building which has been altered to conserve
energy or to minimize infiltration, the boiler area
shouldbeconsideredasaconfinedspace.Ifthereis
anydoubt,installairsupplyprovisionsforcombustion
andventilationinaccordancewithsection5.3,Airfor
Combustion and Ventilation, of the NFPA 54 1988
code,therecommendationsthatfollow,orapplicable
provisions of the local building codes.
3. When the boiler is installed in an unconfined
space, in a building of unusually tight construction,
air for combustion and room ventilation must be
obtained from outdoors or from spaces freely
communicating with the outdoors. A permanent
opening or openings having a total free area of not
less than 1 square inch per 5,000 BTU per hour of
total input rating of all appliances shall be provided.
Ducts may be used to convey make-up air from the
outdoors and shall have the same cross-sectional
area of the openings to which they are connected.
4. When air for combustion and room
ventilation is from inside buildings, the
confined space shall be provided with two
permanentopenings,onestarting12inches
from the top and one 12 inches from the
bottomoftheenclosedspace.Eachopening
shallhaveaminimumfreeareaof1square
inch per 1,000 BTU per hour of the total
inputratingofallappliancesintheenclosed
space,butmustnotbelessthan100square
inches. These openings must freely
communicatewiththeinteriorareashaving
adequate infiltration from the outside.
(Figure 1)
5. When the boiler is installed in a confined space
andallairisprovidedfromtheoutdoors,theconfined
spaceshallbeprovidedwithtwopermanentopenings,
one commencing within 12 inches from the top and
one commencing 12 inches from the bottom of the
enclosure.Theopeningsshallcommunicatedirectly,
or by ducts, with the outdoors or spaces (crawl or
attic) that freely communicate with the outdoors.
One of the following methods must be used to
provideadequateairforventilationandcombustion.
A.Whendirectlycommunicatingwiththeoutdoors,
each opening shall have a minimum free area of
1 square inch per 4,000 BTU per hour of total
input rating of all equipment in the enclosure.
(Figure 2)
FIGURE 1
