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Sizing the Combustion Air Intake Ductwork
The combustion air flow rate requirements per boiler model are summarized in 3.4.3. When sizing the
combustion air intake ductwork, the pressure drop through this ductwork MUST NOT exceed 0.22"
W.C. as described in the table below:
™
P-K STORM
Boiler Model
ST-1250, ST-1500,
ST-1750, ST-2000
ST-1250, ST-1500,
ST-1750, ST-2000
If the combustion air intake ductwork and the exhaust vent terminate on the same wall of
NOTE:
the building, they must utilize the same type of termination fitting.
Patterson-Kelley recommends including a motorized combustion air damper in each
NOTE:
appliance's air intake ductwork. Refer to
Motorized Combustion Air Dampers
Patterson-Kelley recommends, and most
installation codes require, the use of motorized
combustion air dampers with end limit switches
installed in the combustion air intake ductwork
upstream of each appliance. This damper isolates
the combustion air supply when the appliance is in
standby. Once the appliance receives a call for
heat, the motorized combustion air damper opens,
and the end limit switch must close before the
appliance can proceed to ignition. Patterson-
Kelley offers motorized combustion air dampers
with built-in end limits switches for sale, which are
summarized in the table below:
Table of Recommended Motorized Combustion Air Dampers
Combustion Air Ductwork
Size
8"
10"
12"
These normally-closed motorized combustion air dampers operate on 120 VAC and feature a built in
end limit switch which must be wired to the appliances' Air Damper Interlock circuit. Upon a call for
heat, the boiler's Air Damper Relay energizes, which drives the damper motor open. Once the damper
reaches the fully-open position, the end limit switch makes contact and closes the Air Damper Interlock
circuit, allowing the appliance to proceed to ignition. The diagram on the next page shows the wiring
necessary to install the normally-closed motorized damper.
Revised: October 2, 2019
Released: October 2, 2019
Flue Vent Category
through Combustion
II
IV
3.4.5
below for
Normally-Closed
Motorized Damper
10-0490-6944
10-0490-6945
10-0490-6946
Patterson-Kelley 2019
All Rights Reserved.
P-K Storm
Technical Service 1.877.728.5351
Maximum Allowable
Pressure Drop
Air Ductwork
0.22" W.C.
0.22" W.C.
more information.
A
B
8"
8"
10"
10"
12"
12"
2691000099 P-K Storm Installation and Owners
TM
Gas Fired Boiler
Allowable Vent
Pressure
-0.01" W.C. to
-0.05" W.C.
+0.01" W.C. to
+0.22" W.C.
C
D
11"
2.38"
13"
3.38"
15"
4.38"
Manual.docx
Page 22
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