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6
All Air From Outside The Building
When installed in a confined space without utilizing the intake
air option two permanent openings communicating directly with,
or by ducts to, the outdoors or spaces that freely communicate with
the outdoors must be present. The upper opening must be within
12 in, 305 mm of, but not less than 3 in, 76 mm from, the top of the
enclosure. The bottom opening must be within 12 in, 305 mm of,
but not less than 3 in, 76 mm from, the bottom of the enclosure.
Wheredirectlycommunicatingwiththe outdoorsorcommunicating
with the outdoors through vertical ducts, each opening shall have
a minimum free area of 1 in2/4000 Btu/hr, 550 mm2/kW of
the total input rating of all of the equipment in the enclosure.
Wherecommunicatingwiththe outdoorsthroughhorizontal ducts,
eachopeningshall haveaminimumfreeareaof1 in2/2000Btu/hr,
1100 mm2/kWofthetotalinputratingofalloftheequipmentinthe
enclosure. When ducts are used, they must have the same cross-
sectionalareaas thefreeareaof the openingtowhichtheyconnect.
When calculating the free area necessary to meet the make-up air
requirements of the enclosure, consideration must be given to the
blockage effects of louvers, grills and screens. Screens must have a
minimum mesh size of 1/4 in, 6.4mm. If the free area through a
louver or grill is not known, ducts should be sized per Table 3.
Table 3 Make-up Air Louver Sizing
Required Cross Sectional Area
Input
(MBH)
1/4 in 6.4 mm
Wire Screen
75% Free Area
Metal Louvers
25% Free Area
Wooden Louvers
in2cm2in2cm2in2cm2
300 75 484 100 645 300 1935
400 100 645 133 860 400 2581
600 150 968 200 1290 600 3871
750 188 1210 250 1613 750 4839
900 225 1452 300 1935 900 5806
1050 263 1694 350 2258 1050 6774
1350 338 2177 450 2903 1350 8710
1500 375 2419 500 3226 1500 9677
1950 488 3145 650 4194 1950 12,581
2100 525 3387 700 4516 2100 13,548
Canadian installations must comply with CSA B149.1 when air
supply is provided bynaturalairflowfromthe outdoorsfornatural
draft, partial fan-assisted, fan-assisted, or power draft-assisted
burners, there shall be a permanent air supply opening(s) having
a cross-sectional area of not less than 1 in2per 7,000 Btuh
(310 mm2per kW) up to and including 1 million Btuh, plus
1in2per 14,000 Btuh(155 mm2per kW) in excess of 1million
Btuh.
Intake Air Option - General Guidelines
This configuration provides combustion air directly to the boiler/
waterheater's air intakeusingadedicatedpipe toobtaincombustion
air from the outdoors. Combustion air can be drawn in horizontally
throughthe sameoutside wallwhich terminates theexhaustgasesor
vertically through the roof, see Figures 4, 5, 6 & 7.
Common intake air systems may be used provided
the common duct is sized properly and an intake
combustion air damper is installed in the intake air
pipe of each heater. Improper installation can result in
excessive levels of carbon monoxide which can cause
severe personal injury or death!
Single wall galvanized smoke pipe, single wall aluminum pipe or
flexible aluminum pipe can be used for the intake air pipe. It must be
sized per Table 4. All joints in metal combustion air systems must be
securedusingcorrosionresistantfastenersand sealedusinga suitable
Siliconecaulk.ThecombustionairsystemMUSTbesupported
by the building structure not the boiler/water heater.
Table 4 Intake Air Pipe Sizing
Model Size Pipe Diameter
in mm
300 & 400 8203
600 & 750 8203
900 & 1050 10 254
1350 - 2100 12 305
A stack damper interlocked with the unit should be
installed in the intake air pipe when the infiltration of
sub-freezing air could occur, otherwise the unit could
freeze up voiding the warranty!
Intake Air Option - Horizontal Guidelines
The maximum equivalent length for the horizontal combustion
air pipe on installations that used the Direct Vent option is 35 ft,
10.8 m. The maximum equivalent length for the horizontal
combustion air pipe on installations that use the Horizontal Power
Vent option is 100 ft, 30.5 m. Each 90° elbow and the combustion
air terminal are equal to 10 linear ft, 3.0 m of pipe. If horizontal
runs exceed 5 ft, 1.5 m theymustbesupportedat3 ft,0.9 m intervals
with overhead hangers. The certified combustion air terminal from
RBI must be used and installed as shown in Figures 4 and 5.
Intake Air Option - Vertical Guidelines
The maximum length for the vertical combustion air pipe is 30 ft,
9.1 mplus two90°elbows.A listed,nonrestrictivecombustionaircap
must be used. The combustion air cap must terminate as shown in
Figure 6. The penetration point in the roof must be properly flashed
and sealed.
