Combustion Air and Ventilation
for Appliances Located in
UnconfinedSpacesUnconfinedSpaceisaspacewhose volume isnot lessthan50
cubicfeet.per1,000 .B.tu.perhourof theaggregate inputrating
ofall appliancesinstalledinthatspace.Roomscommunicating
directlywiththe spacein which the appliances are installed,
throughopeningsnot furnished with doors, are considereda
partof theunconfinedspace
Inunconfinedspacesin buildings, infiltrationmay be adequate
toprovide air for combustion,ventilation and dilution of flue
gases.However,inbuildings of tight construction(forexample,
weatherstripping,heavily insulated,caulked, vapor barrier,
etc.),additional air may need to be provided usingthe methods
describedin Combustion Air andVentilation for Appliances
Locatedin Confined Spaces,b.
Combustion Air and Ventilation
for Appliances Located in
Confined Spaces
Confined Spaceisa spacewhose volume is less than 50 cubic
feetper 1,000 Btu per hour of the aggregateinput rating of all
appliancesinstalled in that space.
a.ALLAIR FROMINSIDE BUILDINGS:
(SeePage8Figure 1,and Figure2 below)
Theconfined spaceshall be provided with two permanent
openingscommunicating directly with an additional room(s)
of sufficient volume so that the combined volume of all
spacesmeetsthe criteria for an unconfined space. The total
inputof all gas utilization equipment installed in the com-
bined space s.hallbe considered in making th s determina-
tion. Each opening shall have a minimum free area of one
squareinch per 1,000 BTUper hour of the total input rating
of all gasutilization equipment in the confined spade, but
not less than 100 squareinches. One opening shall com-
mencewithin 12 inches of the top and one commencing
within 12 inches of the bottom of the enclosure.
,-_i..:,::.i..
b.ALL ,AIRFROM OUTDOORS: (seeFigures3-5)
The confined space shall be provided with two perma-
nentopenings, one commencing within 12 inches of the
topand Onecommencing within 12 inches from the bot-
tom of the enclosure. The openings shall communicate
directly,or byducts, with the outdoors or spaces (crawl or
attic)that freely communicate with the outdoors.
_qrulloH LOUW_
1. When directly communicating with the outdoors, each
opening shall have a minimum free area of 1square inch
per 4,000 BTU per hourof total input rating of all equip-
ment in the enclosure. (See Figure3.)
2. When communicating with the outdoors through vertical
ducts, each opening shall have a minimum free area of 1
squareinch per 4,000 BTU per hour of total input rating
of all equipment in the enclosure. (SeeFigure4.)
CHIMNEY OR GAS VENT
VENTUL.TION LOUVERS
AIR OUTLET
WATER HEATER
FURNACE
INLETAIR DUCT
Il (e_ 1'abo_ _c_)
Figure4
3.When communicating with the outdoors throughhorizon-
tal ducts, each opening shall have a minimum free area of
1square inch per 2,000 BTU per hour of total input rating
of all equipment in the enclosure. (SeeFigure5.)
IFigure 5[
4.
,
,
=_
_-.: R
When ducts are used,they shall be of the samecross-sec-
tional area as thefree area of the openings to which they
connect. The minimum shortside dimension of rectangular
air ducts shall not be lessthan 3 inches. (SeeFigure 5.)
Louversand Grilles:In calculating freearea, consideration
shall be given to the blocking effect of louvers, grilles or
screens protecting openings. Screens used shal| not be
smallerthan 1/4inclhmesh. If the free area through a design
of louver or grille is known, it should beused in calculat-
ingthe size opening required to provide thefree area spec-
ified. If the designand free areais not known, it may be
assumedthat wood louvers will be 20-25 percent free area
and metal louvers and grilles will have 60-75 percentfree
area.Louversand grilles shall be fixed in the open position
or interlocked with the equipment sothat they are opened
automatically during equipment operation.
Special Conditions Created by Mechanical Exhaustingor
Fireplaces:Operation of exhaustfans, ventilation systems,
clothesdryers or fireplaces maycreate conditions requiring
special attention to avoid unsatisfactory operation of
installedgas utilization equipment.