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Discussion Starter · #1 · (Edited)
This is a home furnace in Northern Pennsylvania, in a "Snow-Belt" area. We had 6"+ from Dec. 1st thru March 31st this past winter. While the home is only 21 years old, this is not the original furnace, although replaced before we purchased the home. You can see the original PVC exhaust vent capped with insulation, right next to the register mounted on the duct.

Is this the correct way to side vent an 80% furnace?
Can PVC be used on this furnace?
Is double wall really going to reduce the moisture buildup?

I cannot find the Installation Chart in/around the furnace. Clearly it was a botch job in my opinion, lowest cost bidder, but the options for getting through the roof are very small, so I need to figure something else out.

Moisture appears to be a significant problem; but my understanding is that PVC is not approved for an 80% Gas Furnace, and the Single Wall used rotted out; even though the furnace is in a heated, insulated basement space. Is the double wall going to help? Is it more 'legal'?

I have created more upward slope in my replacement double wall, versus the single wall that was practically level.
 

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pvc is NOT acceptable in this application. also, as far and horizontaly the flue pipe is running, I REALLY recommend a vent pipe fan installed in the flue. Carbon monoxide poisoning is likely if you leave it like this.
 

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I suggest you run, as fast as you can, to the nearest International Code Council and purchase the latest copy (2012) of the International Fuel Gas Code. Then, spend some time with it, specifically the Venting Section. Then, you will know the answer to your question.:)
 

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Moisture appears to be a significant problem; but my understanding is that PVC is not approved for an 80% Gas Furnace, and the Single Wall used rotted out; even though the furnace is in a heated, insulated basement space. Is the double wall going to help? Is it more 'legal'?
The whole point of proper venting, besides the obvious, is to get the combustion gases out of the vent piping before condensing takes place. Double wall pipe reduces the rate of heat transfer between the hot gases and surrounding air, which will eliminate or reduce the amount of condensing.

The water condensed from the gases contains some corrosive stuff, which eats on the metal.

You may see a lot of single wall piping used for venting, but it's sub-code, at least in my area.

You can likely get a guide for venting at a wholesale house, or you can download a PDF from the link below.

http://www.hartandcooley.com/Products/venting/b-vent/hart-and-cooley-type-b-gas-vent.aspx
 
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