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• Obtain the correct adapter for attaching and sealing to the VT3 5-7/8 inch vent connection outlet from the
manufacturer of the listed Category III or IV venting system being installed. Attach this adapter to the VT3 vent
connection outlet following the instruction provided by the adapter’s manufacturer.
• Follow the Category III or Category IV vent manufacturers’ instruction for installation, sealing and support of their
vent system.
• For proper vent operation and to protect the gas vent from wind and weather, use ONLY the listed vent terminal
specified by the Category III or Category IV vent system manufacturer.
• IMPORTANT: Do not use a barometric damper when applying Category III or Category IV venting.
• This product uses the positive pressure generated by the burner system blower to push combustion products out
of the vent. The vent system must be a stainless steel and UL, ULC, ETL, or CSA certified for use with an
appliance requiring a Category III or Category IV, pressurized vent system. Seal all joints and support horizontal
lengths of vent and follow all installation instructions required by the vent manufacturer.
WARNING: Use only stainless steel venting listed by a nationally recognized testing laboratory for Category
III or Category IV, positive pressure, gas appliance venting. Use of plastic pipe of any type or use of venting
material other than specified in these instructions can result in failure of the venting system and/or exposure
to carbon monoxide, which can result in property damage, personal injury or death.
WARNING: When using Category III or Category IV venting, do not connect this appliance to an existing or
traditional gas vent or chimney or combine the vent with any other appliance, except as provided in Section
8.3.3 “Combining Category III or Category IV Vents.” Such venting could result in failure of the venting
system and/or exposure to carbon monoxide which can result in property damage, personal injury or death.
7.3.1 Maximum Category III or Category IV Vent Length (Equivalent Length)
If a vertical or horizontal Category III or Category IV vent system is used with this appliance, the maximum length
of field supplied venting is shown in the chart below titled Maximum Category III – Category IV Vent Equivalent
Length.
Maximum Category III – Category IV Vent Equivalent Length
Vent Size 6” Vent 7” Vent 8” Vent 9” Vent
Max Equivalent Length
100 feet 130 feet 250 feet 450 feet
Pipe fittings reduce the maximum allowable vent length. Use the Category III or Category IV vent manufacturer’s
equivalent length deduction for all elbows, terminations, etc. If the information is not readily available from the vent
manufacturer, use the Vent Fitting Equivalent Length chart below to find the total equivalent length for all vent fittings
in your combustion air system. Then subtract this number of feet from the total equivalent length allowed in Maximum
Category III – Category IV Vent Equivalent Length chart above. The sum of this calculation is the maximum length of
straight vent allowed. If a longer length is required, repeat the calculation using a larger vent size. When using this
chart, no additional deduction is required for the addition of the vent system terminal.
The following vent information is provided for use in design calculations, if needed.
Venting Specifications
Boiler
Input Mbtu
Required
Air (cfm)
Max Vent
Press. "W.C.
1500 350 1.7
1800 420 2.0
2000 467 2.0
Vent Fitting Equivalent Length
Vent Pipe: 6” Vent 7” Vent 8” Vent 9” Vent
90º Elbow 8 feet 9 feet 10 feet 11 feet
90º Long Radius Elbow 5 feet 5 feet 5 feet 6 feet
45º Elbow 5 feet 5 feet 5 feet 5 feet
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