Finned copper tube gas boilers & water heaters – Boiler Manual
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.
Where directly communicating with the outdoors or communicating
with the outdoors through vertical ducts, each opening shall have a
minimum free area of
1 in
2
/4000 Btu/hr
,
550 mm
2
/kW
of the
total input rating of all of the equipment in the enclosure.
Where communicating with the outdoors through horizontal
ducts, each opening shall have a minimum free area of
1 in
2
/2000
Btu/hr
,
1100 mm
2
/kW
of the total input rating of all of the
equipment in the enclosure. When louvers and screens are used, they
must have the same cross-sectional area as the free area of the
opening to which they connect.
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
in
2
cm
2
in
2
cm
2
in
2
cm
2
399
100
645
133
858
399
2573
600
150
968
200
1290
600
3870
750
190
1210
250
1613
750
4840
1050
263
1696
350
2258
1050
6773
1200
300
1936
400
2580
1200
7740
1480
370
2388
494
3182
1480
9546
1650
413
2662
550
3548
1650
10,643
1970
493
3179
657
4236
1970
12,707
2300
575
3711
767
4945
2300
14,835
Canadian installations must comply with CSA B149.1 when
air
supply
is provided by natural air flow from the outdoors for
natural
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 in
2
per
7,000 Btuh
(310 mm
2
per kW)
up to
and including
1 million Btuh,
plus
1 in
2
per 14,000 Btuh
(155 mm
2
per kW)
in excess of
1
million Btuh
.
Intake Air Option - General Guidelines
This configuration provides combustion air directly to the boiler/
water heater’s air intake using a dedicated pipe to obtain combustion
air from the outdoors. Combustion air can be drawn in horizontally
through an outside wall or vertically through the roof, see Figures
4, 5, 6 & 7.
Common intake air systems may be used to provide
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 in-take air pipe. It must
be sized per Table 4. All joints in metal combustion air systems
must be secured using corrosion resistant fasteners and sealed using
a suitable Silicon caulk or tape.
The combustion air system
muSt be supported by the building structure not the
boiler/water heater.
Table 4 Combustion air pipe sizing
Model Size
Pipe Diameter
in
mm
400
6
152
600 - 750
8
203
1050
10
254
1200 - 2300
12
305
A combustion air 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 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
they must be supported at
3 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 m
plus two 90° elbows. A listed, nonrestrictive combustion air
cap 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.
