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Old 10-18-2010, 12:03 AM   #1
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2 pipe venting

I am installing a Carrier 58MEC060, gas fired furnace.
I want to vent THROUGH ROOF (11/2" x 12' schedule 40 pipe + 2 elbows) AND use combustion air ( 11/2" X 8' Schedule 40 pipe + 2 elbows THROUGH WALL. All installation instructions only show both pipes through roof or both through wall. Is it acceptable to vent through roof and pull combustion/makeup air through wall?


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Old 10-18-2010, 04:39 AM   #2
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They need to be in the same pressure zones. If you have the intake thru the wall. The wind can cause the furnace not to run. Or not to be able to prove enough negative pressure in the heat exchanger.

Run the pipes in 2" thru the roof, and use a concentric termination/vent. Only 1 hole thru the roof then.


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Old 10-18-2010, 06:29 AM   #3
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Beenthere is correct.

Some examples of how pressure differences in differing atmospheric pressure zones are created as wind moves over a structure:

- http://www.woodheat.org/chimneys/windbacksplit.gif

Here’s a diagram of how a concentric through-wall or roof vent is installed:

Typical installations instructions for a concentric through-wall or roof vent:

Home Inspections, Infrared (Thermal Imaging) Leak Identification and Inspection Services, Roof, Attic, Building, Basement and Foundation Moisture Intrusion and Water Leak Inspections, Troubled Building Consultations - Serving Chicago and Suburbs http://paragoninspects.com/
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