Category Ii Installations; Category Iv Installations - Patterson-Kelley P-K MACH CM300 Installation & Owner's Manual

3.5.11 Category II Installations

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The P-K MACH 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 stainless steel vent adapter is required to mate the boiler exhaust connection and the vent pipe.
See the table below for the applicable part numbers.
2. A normally-closed motorized damper is required on the boiler's air intake. See the table below for
the applicable part numbers.
3. Ensure the flue venting system is designed to maintain a slightly negative draft, measured inside
the vent at the rear of the boiler, between -0.01" W.C. and -0.04" W.C. Excessive negative draft
will cause nuisance trips such as flame failures.
4. The vent system must be properly drained of condensate before returning to the boiler.
Table of Required Stainless Steel Vent Adapters and Category II Motorized Dampers
Nominal
Boiler Size
Stack Size
CM300
CM399
CM500
C750
C900
C1050
The normally-closed motorized damper operates on 120 VAC and features an end limit switch wired
into the boiler's air damper interlock circuit. Upon a call for heat, the boiler's damper relay will energize
and drive the damper open. Once the damper reaches the fully-open position, the end limit switch
makes contact and closes the air damper interlock circuit allowing the boiler to fire. The diagram below
shows the wiring necessary to install the normally-closed motorized damper.
Other damper motor voltages are acceptable, provided they do not exceed 240VAC. 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.

3.5.12 Category IV Installations

If the vent installation is designed for Category IV conditions only (condensing – positive pressure) as it
is defined in ANSI Z21.13/CSA 4.9, latest edition, the 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.
Do not use a barometric damper if operating with a positive stack pressure (Category IV).
Harmful flue gases may leak into the room which can cause serious injury or death.
Revised: January 3, 2020
Released: January 3, 2020
Stainless Vent
Adapter
6" 2620000181 (OEM)
6" 2620000181 (OEM)
6" 2620000181 (OEM)
6" 2620000181 (OEM)
8" 2620000366 (OEM)
8" 2620000366 (OEM)
 Patterson-Kelley 2020
All Rights Reserved.
P-K MACH
Technical Service 1.877.728.5351
Normally-Closed A
Motorized Damper
6"
1004906943
6"
1004906943
6"
1004906943
6"
1004906943
8"
1004906944
8"
1004906944
1004905980 P-K MACH CM300-CM500&C750-C1050
Installation and Owners Manual (Rev F Jan-2020).docx
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Gas Fired Boiler
B C D
6" 9" 1.38"
6" 9" 1.38"
6" 9" 1.38"
6" 9" 1.38"
8" 11" 2.38"
8" 11" 2.38"
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