Specs for PVC Direct Vent Pipe

[randynavarro]

Been to most of the mfg's websites trying to get the install instructions for their direct vent, high efficiency furnaces and water heaters.

They post owner's manuals, but not install instructions.

Trying to get info. specifically on maximum lenghts of pipe, elbows, pitch etc.

Anybody have any good sources?

[Bill Kibbel]

I have a few manuals for the most common models I see. Let me know if you need something specific and I'll check.

A similar topic was discussed here:

https://inspectorsjournal.com/forum/topic.asp?TOPIC_ID=3043

[randynavarro]

Bill, thanks for the offer. I'll wait on it. Don't want you to go through extra work.

Thanks also for that link - I looked in prior threads and didn't find that one.

The Goodman manual on that old thread was helpful, but didn't address the pitch of the pipe.

I had one yesterday that turned down out of the basement ceiling for about 24" and then out the sidewall. That Goodman manual doesn't address the pitch of pipe specifically.

[rjw]

Whenever I run across the actual installation manuals, if I have "alone time" I glance over them (while my client is reading and signing the contract)

There is significant variation between manufacturers and even models.

I prefer to avoid creating an impression in my client that I am responsible for knowing the installation specifics for every model of 90+

If I have seen a 'potential' problem and find a specific reference in an available installation manual, I'll use it, but I otherwise leave it to "the experts."

Size/length of the vent depends on model, angles, etc. Charts required.

Pitch: my understanding is they should always be pitched back 1/4" ft back to the furnace.

FWIW, the biggest mistake I see is that they discharge too low above grade: in the US, every manual I have seen says 12" above grade or the 'anticipated snow cover, 18" in Canada"

[JEuriech]

See following Goodman Two-Stage Gas-Fired Warm Air Furnace PDF http://www.dnmech.com/lit/IO-243.pdf Page 12, 17, and 18.

Horizontal runs of vent/flue piping must be supported every three feet and must maintain a 1/4 inch per foot downward slope, back towards the furnace, to properly return condensate to the furnace’s drain system. Allowances should be made for minor expansion and contraction due to temperature variations. For this reason, particular care must be taken to secure piping when a long run is followed by a short offset of less than 40 inches.

Vent pipe terminates 12" min. above highest anticipated snow level.

Jeff Euriech

Peoria, Arizona

[hvacman]

The other very missed aspect of the direct venting of 90% furnaces is the vent pipe size. Manufactures state different pipe sizes based on BTU input of unit and venting length, where say a 75,000btu/hr unit may use 2 inch and a 100,000 btu/hr unit will use 3 inch. The install manual and the respective venting chart is really the key, there is no rule of thumb here. ........hvacman

[mortan]

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