Thread: vent pipe

Is PVC pipe used as ventilation piping on a furnace other than high effeciency units? The year is 1998 on this furnace.

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Only if you want to burn the house down.

PVC is used on 90% and up furnaces only. Anything less than 90% has flue temps too high for the PVC to handle.

Thank you very much. I'll be glad when I can answer questions instead of asking questions.

PVC has a design temp. rating of 140*F but would be better if kept under 110*F. Growing information on failures at higher temp range for extended periods. The use of PVC is under ASSumption by the codes. Very little data on performance in vitro or in vivo. Could become the next Plexvent/ UltraVent. The main thing saving this pipe for Cat. IV venting is the amt. of air moving through the system. Reduce your air flow, such as from an obstructed vent termination or ice dam in a low point and you can overheat it back at the appliance collar and crack the pipe.
Stay tuned.

That just means it needs to be properly installed. Mines been in for 14+ years and is in good shape.

Kevin,

There were category IV (hi-efficiency) furnaces in 1998, and even eariler, that would properly use PVC as the exhaust vent. But they may look a bit different than the newer furnaces being installed today. And, you will run across a few odd ball situations with heating systems different than the standard forced air system (hot water boilers, Coleman wall furnaces, etc that will be all kinds of confusing for a while in your early experience as an inspector).

But for almost every standard furnace, you should locate the manufacturer's specification lable, somewhere inside the cabinet of the furnace. It will state whether it is a Category I (mid efficiency) or Cat IV furnace. I always make it a point in my inspection to document the manufacturer, serial number (so I can figure out manufacture date), the BTU/HR rating, and whether it is a Cat I or Cat IV furnace type.

(Old furnaces made before these designiations would of course not have this, but then they would also HAVE TO use metal exhaust flues anyway - at that point, you're back to figureing out whether the exhaust is single or double-wall).

The burners might be open (unlike the Cat IV furnaces currently being made), and therefore at first glance look like a Cat I furance. But the obvious tell-tale indicator is that it would have a draft induction fan. Also, because the exhaust temperature is lower, Cat IV systems should have something to capture and drain condensatation. It may or, may not, have a second PVC pipe for the combustion air intake. Eariler Cat IV furnace installations often did not have a direct intake (you will occasionally even see a newer Cat IV furnace without a direct intake vent), and only rudimentary condensate draining.

It is also worth your time to occasionally grab the furnace installation manual that is supposed to be lying around nearby, and look it over. Or get the model number and try to find it on the internet (difficult with older models). I don't know about the HVAC guys in your area, but think only a few HVAC installers around here even know how to read, much less bother to read the stinking install manual. Even a quick review of a variety of these manuals over time will help build your knowledge and confidence.

For this type of application, FG36 passed last cycle and the 2009 ICC FG will say something to the effect of:

Follow the instructions of the appliance manufactuer for vent piping material and installation.

I think this is good practice for everyone, but good luck finding the appliance manual 10 years out.

The trick here is if someone replaces a condensing unit for something else. That could be very bad.

Que Pasa?
No necesito un stinking manual