Ducting Requirements - Rheem HB Duct Ready Series Use & Care Manual

Table 1.- Maximum Duct Length.
Duct Type / Diameter
Rigid
Flexible

Ducting Requirements

Always check with local building and
HVAC codes before designing the duct
system
The water heater may be ducted to the
outdoors or another space as described in
these instructions. Ducting configurations
that does not comply with these
guidelines are not supported.
DO NOT connect this water heater to
existing duct work; it must be ducted
separately from other appliances.
Ducting approved for HVAC applications
is required.
Ducting must be adequately supported
along both vertical and horizontal
lengths.
UL Certified terminations must be
used for ducting to the outside. These
terminations have been evaluated to
ensure there is sufficient protection
from rain water entry and resistance to
air flow is minimized.
Indoor registers approved for HVAC
applications is required.
Rigid ducting must be isolated from
floor joists or other structural members
to minimize the transmission of noise
and vibration. A short section (12
inch minimum) of flexible duct must
be used between the water heater and
rigid ducting as an isolation method.
Duct System Configuration
The inlet and outlet ducting
connections on the water heater
accepts 8 inch diameter ducting. No
additional adaptors are needed.
7 inch, 6 inch, 5 inch diameter
ducting is supported. Table 1 lists the
total feet of ducting allowed. For
duct diameters smaller than 8 inch
8"
340'
125'
Every foot of flexible ducting counts as
three feet of rigid ducting.
Ducting must be insulated per HVAC
codes (to prevent condensation).
Ensure cold air exhaust is sufficiently
away from structures to prevent
condensation on surfaces.
Maximum heater performance is
obtained by lowering the resistance to
air flow (regular filter maintenance is
beneficial) and providing the unit with
warm moist air.
Considerations when planning the duct
system:
Run the ducting the most direct

route possible.
Limit the number of elbows/bends.

Use the largest duct size possible.

Use the largest termination possible.

Consider placement and direction of

terminations (reduce recirculation of
exhaust into the intake).
Calculated length of duct is the
length on the inlet plus the length
on the outlet. Any combination of
duct lengths on the inlet and outlet is
supported up to the maximum duct
length (Table 1).
diameter, Table 1 takes into account
the duct reducer(s) and up to 10 feet
of 8 inch rigid ducting (two elbows)
before the duct reducer(s) at the unit.
Duct Reducers must be installed
within 10 feet (two elbows) of the unit
or within 2 feet of the end of the duct.
7" 6"
160' 65'
65' 25'
5"
17'
--
11