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Why can't I use regular duct to vent the chimney on the outside of the house?

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We have an old furnace that vented through the chimney,but we took the chimney down and want to replace it with pipe.  I don't understand why we have to use the double insulated pipe instead of the regular when it's outside.
asked in House Chimney by snyderkj (120 points)
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1 Answer

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Hi Snyderkj,

The best way to find out would be by asking your local building / mechanical code enforcement authorities. I have no idea where are you located (climate is one thing) and what local codes apply in your particular area.

One of the reasons behind using the double wall pipe over the single wall pipe are fire safety, in case that single wall pipe touches any combustible materials.

Second is the condensation that might develop while using a single wall vent pipe. Condensation, besides accelerating corrosion of the pipe itself, may flow back into the furnace deteriorating its components.

I'd need much more information and details about your installation to provide more precise answer, but your safety is the main reason behind the double wall vent pipe requirement.
answered by darekrudy (21,730 points)
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