Navien NHB-055 Installation & Operation Manual page 43

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 44 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-055
Maximum
Input 55,000
(BTU/H)
Outdoor
make
up air is
14 in 2
provided, a
6 in (W) x
minimum
3 in (H) or
free area
5 in round
2
of 1 in ,
per 4,000
BTU/H
Indoor
make
up air is
provided, a 55 in 2
minimum 7 1/2 in (W)
free area x 7 1/2 in (H)
of 1 in 2
per 1,000
BTU/H
NHB-080 NHB-110 NHB-150
80,000 110,000 150,000
20 in 2 28 in 2 40 in 2
7 in (W) x 10 in (W) x 10 in (W) x
3 in (H) or 3 in (H) or 4 in (H) or
5 in round 6 in round 7 in round
80 in 2 110 in 2 150 in 2
9 in (W) x 10 1/2 in (W) x 12 1/4 in (W) x
9 in (H) 10 1/2 in (H) 12 1/4 in (H)
Venting the Boiler 43