Category Ii/Iv Flue Gas Exhaust Vent Planning - Patterson-Kelley P-K STORM ST-8000 Installation And Owner's Manual

Category II/IV Flue Gas Exhaust Vent Planning

Several codes and standards have categorized appliances in accordance with the flue gas temperature
and pressure produced by the appliance. The applicable categories are defined as follows:

Category II: An appliance that operates with a non-positive vent static pressure and with a vent
temperature that may cause excessive condensate production in the vent.

Category IV: An appliance that operates with a positive vent static pressure and with a vent
temperature that may cause excessive condensate production in the vent.

Direct Vent: An appliance that is constructed and installed so that all air for combustion is
derived directly from outdoors and all flue gases are discharged to the outdoors.
All P-K STORM boilers are dual-certified as Category II or IV appliances,
®
Z21.13/CSA 4.9, latest edition. The P-K STORM
negative to slightly positive exhaust pressure. It is critical to ensure the flue vent material is certified for
Category II or IV operation.
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. for the 2500-4000 and MUST NOT exceed 0.5" W.C. for the 5000-8000 as described in the table
below:
P-K STORM ® Boiler Model
ST-2500, ST-3000, ST-3500,
ST-4000
ST-5000, ST-6000, ST-8000
ST-2500, ST-3000, ST-3500,
ST-4000
ST-5000, ST-6000, ST-8000
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
NOTE: ST-2500-ST-4000: Total combined vent pressure not to exceed 0.44" W.C.
ST-5000-ST-8000: Total combined vent pressure not to exceed 1.0" W.C.
The vent material to be used for US and Canada is listed in the Table of Acceptable Materials for
Venting Systems located in 2.5.4.
Vent installations shall be in accordance with NFPA 54/ANSI Z223.1, the National Fuel Gas Code, or
CAN/ CSA-B149.1, the Natural Gas and Propane Installation Code, or applicable provisions of the local
building codes.
Revised: February 2, 2024
Released: February 2, 2024
series boilers are capable of operating with slightly
®
Maximum Allowable
Flue Vent Category
through Combustion
II
II
IV
IV
3.4.3 below for
 Patterson-Kelley 2024
All Rights Reserved.
P-K Storm
Technical Service 1.877.728.5351
as defined in ANSI
Pressure Drop
Allowable Vent Pressure
Air Ductwork
0.22" W.C.
0.5" W.C.
+0.01" W.C to +0.44"
0.22" W.C.
0.5" W.C. +0.01" W.C to +1.0" W.C.
more information.
2691000403 P-K Storm ST2500-ST8000
Installation and Owners Manual Rev G.docx
®
Gas Fired Boiler
-0.01" W.C. to
-0.05" W.C.
-0.01" W.C. to
-0.05" W.C.
W.C.
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