M3
CONDENSING WATER BOILER
17
34-1115 12/15
WARNING: Adequate clean combustion air must be provided to the appliance. The appliance must never
operate under a negative pressure. Particular care must be taken when exhaust fans, compressors, air
handling units, etc. may rob air from the appliance. The combustion air supply must be completely free of
any chemicals or fumes, which may be corrosive to the appliance. Some common chemical fumes to avoid
are fluorocarbons and other halogenated compounds, most commonly present as refrigerants or solvents,
such as Freon, trichloroethylene, perchlorethylene, chlorine, etc. These chemicals, when in contact with the
equipment or when burned, form acids which quickly attack the tubes, flue collector, stack and other
appliance and auxiliary equipment. Failure to provide adequate clean combustion air or operating under
negative pressure can cause premature, unwarranted product failure or unsafe operation producing carbon
monoxide that could escape into the building. Exposure to carbon monoxide can lead to personal injury or
death.
7.2 Maximum Allowed Remote Combustion Air Inlet Length (Equivalent Length)
A vertical or horizontal remote air inlet system can be connected to this appliance without modification. The
maximum length of field supplied single wall pipe, such as PVC or galvanized ventilation pipe, is shown in the chart
below titled Maximum Air Inlet Duct Equivalent Length. Use metal tape or RTV sealant to seal each pipe joint.
Maximum Air Inlet Duct Equivalent Length
Duct Size
4”
(Model 400 Only)
4”
(Model 500 Only)
6” Duct
(All Models)
8” Duct
(All Models)
Max Equivalent Length 100 eq. feet
60 eq. feet
150 eq. feet 200 eq. feet
To determine the maximum straight length of duct allowed, use the Duct Fitting Equivalent Length chart below to find
the total equivalent length for all duct fittings in your combustion air system. Then subtract this number of feet from
the total equivalent length allowed in Maximum Air Inlet Duct Equivalent Length chart above. The sum of this
calculation is the maximum length of straight duct allowed. If a longer length is required, repeat the calculation using
a larger duct size. No additional deduction is required for the addition of the duct system terminal.
Duct Fitting Equivalent Length
Duct Pipe: 4” Duct 6” Duct 8” Duct
90º Elbow 22 feet 16 feet 11 feet
90º Long Radius Elbow 12 feet 10 feet 6 feet
45º Elbow 12 feet 10 feet 6 feet
The following remote air duct information is provided for use in design calculations, if needed.
Remote Air Duct Specifications
Input MBtu/h Required Air (SCFM)
399 87
500 108
600 130
650 141
700 152
750 163
800 173
7.3 Remote Combustion Air Cap
A suitable remote air termination must be used to prevent water, debris, animals or obstructing material from entering
the remote air supply.
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