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mysterylectric 12-06-2010 02:07 PM

Gray (Electrical Conduit)PVC for %95 Furnace Intake and Exhaust Vents?

I went looking for 2" pvc to vent my furnace at the local big box building supply store. I expected to buy white PVC sched 40. I found it up to 1 1/4". When I asked where the 2" was, I suggested it might be in the garden section: but the guy said no, they just don't carry 2" PVC,

But I knew PVC is often used in electrical work. I always thought it was Sched 80. 1 isle over, I found 2" gray PVC in sched 40. It's rated 90C, which seems good.

Two advantages I see right off the top is the fact that most pieces and connectors have one end belled: you can go a long way without buying any fitting or couplers. Another feature is that the 90's and 45 have long radius sweeps to simplify wire pulling. Though trivial and worthless in a tight squeeze, in theory these sweeps should lower air resistance.

So does anyone know if I can use this material for venting my 95% furnace? I think the instructions call out sched 40 pvc, no further details.


dhubz 12-06-2010 06:02 PM

I just had my furnace replaced, I was told the only thing that can be used is the white pipe it is called 636 pipe for gas flue, my old furnace had a 2" black ABS which used to be acceptable but apparently it was starting to fail after years of heat exposure. I am no expert but, I don't think the Sch40 PVC will hold up either. I was able to use the black ABS for the intake, which meant I only needed 1 new pipe. hope it helps

hvactech126 12-06-2010 06:07 PM

schd 40 only, check install manual as it details what is acceptable. Never heard of building supply not carrying 2"!

mysterylectric 12-06-2010 07:17 PM

Well, this gray stuff is schd 40. I heard a rumor a few years ago that in my area (San Francisco) PVC is not allowed for DWV plumbing, due to flame spread or smoke generation or something. It may be prohibited for sale in my county. Come to think of it I've never seen it _anywhere_ around here: plumbing supply, hanging out the back of a van, debris boxes, etc. I'm working with a contractor (to double check my work) and he just said "just use pvc for that" referring to the vent. I'll see if I can find the 636 designation in the install manual.

zootjeff 12-06-2010 10:00 PM

59 Attachment(s)
The main point of the venting system is to create an airtight intake and exhaust. The air coming out of your furnace is only 80-90 degrees and you want the pipe water tight. I don't see any reason why the grey stuff wouldn't work and your right about the large radius being a plus too..

You have to silicone terminate to the furnace in most cases anyway so I bet it would work great. The white stuff seems to bond to the grey stuff. Sch40 is thicker then Sch80 and you want the thicker stuff..

See if you can search the net and find out the chemical differences between white and grey, but I bet it would be just fine.

Home Depot carries both.. I had to order white large radius's online..

Home Air Direct 12-06-2010 10:07 PM

Most furnace manufacturers specify Schedule 40. Some also allow Foamcore. I would not deviate from spec:no:

zootjeff 12-07-2010 08:44 AM

59 Attachment(s)
Straight from the installation manual:

Two- or three-inch nominal diameter PVC Schedule 40 pipe meeting
ASTM D1785, PVC primer meeting ASTM F656, and PVC solvent
cement meeting ASTM D2564 specifications must be used.
Fittings must be DWV type fittings meeting ASTM D2665 and ASTM
D3311. Carefully follow the pipe manufacturer’s instructions for
cutting, cleaning, and solvent cementing of PVC.
As an alternative to PVC pipe, primer, solvent cement, and fittings,
ABS materials which are in compliance with the following specifications
may be used. Two-or-three-inch ABS Schedule 40 pipe
must meet ASTM D1527 and, if used in Canada, must be CSA
listed. Solvent cement for ABS to ABS joints must meet ASTM
D2235 and, if used in Canada, must be CSA listed. The solvent
cement for the PVC to ABS transition joint must meet ASTM D3138.
Fittings must be DWV type fittings meeting ASTM D2661 and ASTM
D3311 and, if used in Canada, must be CSA listed. Carefully
follow the manufacturers’ instructions for cutting, cleaning, and
solvent cementing PVC and/or ABS.
All 90 elbows must be medium radius (1/4 bend DWV) or long
radius (Long sweep 1/4 bend DWV) types conforming to ASTM
D3311. A medium radius (1/4 bend DWV) elbow measures 3 1/
16” minimum from the plane of one opening to the centerline of the
other opening for 2” diameter pipe, and 4 9/16” minimum for 3”

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