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Cat IV with B vent


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Is it okay to connect PVC to a B vent?

Nope.

IRC sez vent material "as specified by the manufacturer". All manufacturer's of cat IV furnaces will specifically exclude B-vent.

Just did a building where 10 space heating units were just replaced with cat IV furnaces. I'm guessing the installer didn't want to change the B-vents through the roof.

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B-vent listed to UL 441 for CAT I appliances only. No positive vent pressure. Natural draft only.

Positive vent pressure appliances must vent into pipe listed for positive vent pressure, which is UL 1738 or PMI, which is where the illegal use of PVC comes from. PVC has never been approved for venting in the US by UL nor by IAPMO nor any mfrs. I'm aware of. Still allowed though by IRC for now.

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Positive vent pressure appliances must vent into pipe listed for positive vent pressure, which is UL 1738 or PMI, which is where the illegal use of PVC comes from. PVC has never been approved for venting in the US by UL nor by IAPMO nor any mfrs. I'm aware of. Still allowed though by IRC for now.

What statute is being violated by using PVC to vent cat IV furnaces?
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No statute Bill. As I said, the mfrs. state do NOT use it for combustion venting and IAPMO said don't do it. It is NOT listed to UL 1738 so technically its just some building material that a group of mfr.s decided to use without permission or a listing. It would be the same as using terra cotta sewer pipe with mortar joints and calling that ok.

There is no test protocol to ensure polymeric venting is intact unlike DWV pipe. One problem is the pipe mfrs. specifically forbid the use of pressurized gas including air in testing their pipes, even at low pressures. Nobody wants to do a water test because it will leave a lot of water in the pipes that you have to figure out how to drain. I'm working on a protocol but it is not an easy nut to crack. Meanwhile, there are listed products available.

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I just checked some installation instructions;

Trane says you can use:

  • PVC F891 (cellular core), D2665 (DWV pipe), D1785 (Sch 40, 80, 120), or D2241 (SDR series).

CPVC D2846 (CPVC41), F441 (Sch 40, 80), or F442 (SDR series).

ABS D2661, F628

Carrier says you can use the same things.

Goodman says you can use 1785, D2465, or D2266.

What am I missing?

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Re-read my first post. I said the IRC still allows it. This, however, is a contradiction because the code also says all positive pressure venting must be listed. They can't make their minds up.

These appliance mfrs. say its ok to use this pipe but the pipe mfrs. and other agencies say don't do it. That's all. Fernco says don't use their neoprene couplings for combustion venting but sells them to water heater mfrs. for use on power vented models included with the unit. Go figure.

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Re-read my first post. I said the IRC still allows it. This, however, is a contradiction because the code also says all positive pressure venting must be listed. They can't make their minds up.

These appliance mfrs. say its ok to use this pipe but the pipe mfrs. and other agencies say don't do it. That's all. Fernco says don't use their neoprene couplings for combustion venting but sells them to water heater mfrs. for use on power vented models included with the unit. Go figure.

So the IRC allows it and the furnace manufacturers allow it - heck, they *require* it -- but the pipe manufacturers prohibit it. Yes?

If that's the case, and given that there are millions of these installations out there performing just fine, my decision, as a home inspector, is not to wade into that particular field of weeds.

When you get the manufacturers and the IRC to realize the folly of their ways, let me know and I'll be happy to hop on board.

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Fernco isn't neoprene. It's flexible PVC. It's pretty neat stuff.

Pipe manufacturers not approving it sounds more like corporate legal limiting class action exposure than any inadequacy of the material. Pretty much standard strategy in materials manufacturing.

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