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6.1.2 Non- Direct Venting
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 Bosch 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 installed in a manufactured home (mobile home), all combustion air
must be supplied from the outdoors as described on page 30. When using non-
direct venting, maintain non-direct vent clearances shown on page 32 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:
Insert the elbow into the intake air duct.
Figure 30
Singular Combi Boiler - BTC 439003301 B (2021/07)
Table 10
Intake pipe
Provide two openings to allow for circulation of combustion air as
specified by ANSI Z223.1/NFPA 54 or CAN/CGA B-149.1:
If outdoor make up air is
Maximum
provided, a minimum free
Boiler
Input
area of 1 in², per 4,000
(BTU/H)
BTU/H
40 in²
Singular
155,000
10"(W) x 4" (H) or
4000
7" round"
50 in²
Singular
199,000
10" (W) x 5" (H) or
5200
8" round
Installation Instructions
If indoor make up air is
provided, a minimum free
area of 1 in² per 1,000
BTU/H
150 in²
12 1/4" (W) x
12 1/4" (H)
199 in²
14 1/4" (W) x
14 1/4" (H)
| 31
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