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Inlet Duct Connection to Boiler
Connect the air supply duct to the inlet air collar on the boiler. The air inlet collar is 12" OD (ST-2500-
ST-4000) or 16" OD (ST-5000, ST-6000, and ST-8000). Fasten the air inlet duct to the collar with sheet
metal screws at 90° angles and seal with aluminum tape or sealant.
Intake Duct Materials and Sizes
The air intake duct can be fabricated from PVC, CPVC, single wall galvanized steel, or other suitable
materials. The duct must be rigid enough to maintain the full required cross sectional area under all
operating conditions. Proper sealing of the intake ductwork is necessary to prevent infiltration of air
from conditioned space. Joints in PVC or CPVC must be cemented. For galvanized duct, wrap each
joint and seam with adhesive aluminum tape or other sealant. The installation of a birdscreen on the
intake termination is recommended. Ensure that the screen does not become blocked with snow, ice,
insects, etc.
Category II Installations
The STORM boilers are dual-certified for either Category II or Category IV operation. Category II
appliances operate with a non-positive vent static pressure and with a vent temperature that may cause
excessive condensate production in the vent. There are several requirements for reliable operation of
the boilers under Category II conditions:
1. A normally-closed motorized damper is required on the boiler's air intake. See the table below for
the applicable part numbers.
2. The draft, measured inside the vent at the rear of the boiler, must not exceed -0.05"
Excessive negative draft will cause nuisance trips such as flame failures.
3. The vent system must be properly drained of condensate before returning to the boiler. See
for information on installing condensate drains in the exhaust vent.
Boiler
Nom. vent
Size
ST-2500
ST-3000
ST-3500
ST-4000
ST-5000
ST-6000
ST-8000
A normally-closed motorized combustion air damper with end limit switch is required for Category II
vent installations and is optional for Category IV vent installations. 120VAC motorized dampers with
end limit switches are available for purchase from Patterson-Kelley. Other damper motor voltages are
acceptable, provided they do not exceed 120VAC. The Air Damper Interlock circuit for the end limit
switch is always 120VAC which is sourced from the boiler itself. All end limit switches must be rated for
a minimum 120VAC.
Revised: February 2, 2024
Released: February 2, 2024
Table of Required Category II Motorized Dampers
Boiler Vent
Boiler Combustion
Size
Size
10"
10"
10"
10"
12"
12"
12"
12"
14"
14"
14"
14"
14"
14"
Patterson-Kelley 2024
All Rights Reserved.
Technical Service 1.877.728.5351
Combustion air N.C.
Air inlet
Motorized Damper
12"
1004906946
12"
1004906946
12"
1004906946
12"
1004906946
16"
1005103120
16"
1005103120
16"
1005103120
2691000403 P-K Storm ST2500-ST8000
Installation and Owners Manual Rev G.docx
®
P-K Storm
Gas Fired Boiler
W.C.
3.7.5
Size
12"
12"
12"
12"
16"
16"
16"
Page 41
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