P-K MACH
®
Gas Fired Boiler
Technical Service 1.877.728.5351
Revised: January 3, 2020
Released: January 3, 2020
Patterson-Kelley 2020
All Rights Reserved.
1004905981 P-K MACH C1500H-C4000 Installation and
Owners Manual (Rev F Jan-2020).docx
Page 35
3.5.7 Category II Installations
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 b
oiler’s air intake. See the table below for
the applicable part numbers.
3. The draft, measured inside the vent at the rear of the boiler,
must not exceed -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. See
for information on installing condensate drains in the exhaust vent.
Table of Required Stainless Steel Vent Adapters and Category II Motorized Dampers
Boiler
Size
Nom. vent
Size
Stainless Vent
Adapter
Vent adapter
size
Boiler Combustion
Air inlet
Combustion air N.C.
Motorized Damper
Size
C-1500H
10”
2640000133
10”
10
”
1004906945
10
”
C-2000H
10”
2640000133
10”
10
”
1004906945
10
”
C-2500
10”
2640000133
10”
12”
1004906946
12”
C-3000
10”
2640000133
10”
12”
1004906946
12”
C-4000
10”
2640000133
10”
12”
1004906989
14”
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 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.
