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Non-Direct Venting (Single Pipe)
If, at any time, the installation location could
experience negative pressure, there is a possibility
of back drafting cold air through the boiler's heat
exchanger. This situation could lead to the freezing
of the heat exchanger and malfunction of the boiler.
However, building codes in most jurisdictions
disallow negative pressures in residences. In a
home with a well-balanced air supply, the heat
exchanger should not be in danger of freezing.
Because the cause of back drafting is not considered
a manufacturing problem, any freezing damage
which occurs from back drafting will not be covered
by the Navien warranty. If there is any question
about the possibility of back drafting in the
installation location, use a direct venting system for
the boiler.
When using non-direct venting, maintain non-direct
vent clearances shown on page 60 as required by
ANSI Z21.10.3 and the National Fuel Gas Code,
ANSI Z223.1/NFPA 54, and CAN/CSA B149.1
Natural Gas And Propane Installation Code.
To use non-direct venting for the boiler:
1. Insert the termination end cap into the intake
air duct. Do not glue the end cap, to allow for
easy removal and cleaning of the cap.
Vent Termination
Cap 2"
Coupling 2"
Vent Pipe 2"
2. Provide two openings to allow for circulation
of combustion air as specified by ANSI Z223.1/
NFPA 54 or CAN/CGA B-149.1:
NHB-
055H
Maximum
55,000 80,000 110,000 150,000
Input (BTU/H)
Outdoor
make up air
14 in
2
is provided,
6 in (W)
a minimum
x 3 in
(H) or 5
free area of
1 in
, per
in round
2
4,000 BTU/H
Indoor make
up air is
55 in
2
provided, a
7 /2 in
minimum
(W) x 7
free area of
/2 in (H)
1 in
per 1,000
2
BTU/H
NHB-
NHB-
NHB-
080H
110H
150H
20 in
28 in
40 in
2
2
2
7 in (W)
10 in (W)
10 in (W)
x 3 in
x 3 in (H)
x 4 in (H)
(H) or 5
or 6 in
or 7 in
in round
round
round
80 in
110 in
150 in
2
2
2
9 in
10 /2 in
12 /4 in
(W) x
(W) x
(W) x 12 /4
9 in (H)
10 /2 in (H)
in (H)
Venting for Combustion Air
59
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