I bought a new (40 year old) house recently. It has a gas high efficiency furnace that passed the gas company inspection, so I thought it was OK. But then I saw that there's leaking coming from every single joint in the exhaust pipe. I was told by the home warranty company's person that it was due to improper construction of the joints in the pipe. I did a bunch of research on the exhaust pipe to determine if replacing the pipes with CPVC using the same configuration (but gluing the joints properly) is something I can do myself, or is there something special inside the pipes that needs to be installed?

No cpvc here. You will want to replace all leaking areas with pvc. Clean/prime both the fitting hubs and the pipe then cement both hubs and pipe. Should be a simple do it yourself job, but before I can say for sure, show us a couple pics of your currents exhaust piping.

Have a furnace servicer come and take a look at it. You don't want Carbon Monoxide getting into you home. I must ask, just what is it leaking? If it is water, the pipe is acting as a condenser and the water vapor is building up in the pipe.
Best bet is to have it looked at by a professional.

If the piping is pvc, it is a high efficiency furnace, which creates condensation, so if the joints are not sealed completely, water will leak, as well as combustion by products including carbon monoxide. I agree, you may want to call in an onsite pro here, or simply replace the complete exhaust vent with proper install methods (which a pro will know how to do, of course).

Handyman, do you know anything about high efficiency furnaces? The pipe isn't acting as a condenser, the secondary heat exhanger in the unit is where the condensing occurs. They are designed this way, and without condensation, you don't have a high eff unit (90+).

mygirlsdad77, in your own answer you stated that it is a high efficiency furnace which creates condensation. If the exhaust pipe is cooler than the exhaust traveling through it, there will be condensation in the pipe because there is water vapor in the exhaust.

Sure, but 99.9 percent of the condensation in the pipe comes from the unit itself. Minimal condensation actually occurs in the pipe, but is introduced from the draft inducer blower which is blowing condensed combustion up and out the vent pipe. This is why all 90+ units have condensate drain systems to drain away condensate, but some of that is bound to go up or through the vent. This is why you see ice cycles form on vent terminations. Basically extremely high levels of humidity. I realize your basis of thought on this, but do you deal with these units on a regular basis?

For your theory to hold true (condensation occurring strictly in the vent pipe) that would mean that every 80+ unit would have to have a drain system for condensation in the vent. A correctly sized metal vent on a low efficiency unit will not create condensation. You will only see condensation at the vent termination(and seldom then) when there is no condensation in the unit itself.

Alas, Im not even sure why we seem to be arguing about this. I can tell from your statements that you seem to have a bit of knowledge about such things. However, until you have seen these things first hand, many, many, many times, I see no need to speak of it anymore.

That being said, please do stick around and help out around here. We are always looking for educated folks to help answer peoples questions about HVAC.


Take care.

This will be my last entry to this thread. Before you judge my expertise, and someone here made the distinction between commercial vs residential being vastly different,, well. They are more similar than different. Air is air and it only moves certain ways no matter what the application. The entire conversation about condensation is completely dependent on the environment the equipment is located in. If the high efficiency furnace is in a dry basement, there would be very little condensate anywhere. A damp basement or one with abnormal high humidity, more condensate. I was only commenting on the condensate that is apparently leaking out of the exhaust tube. I believe that this particular installation may be in a high humidity environment. If you want to go into thermo dynamics you can blame the leaks on the colder air that is coming into contact with the exhaust air within the tube. Water vapor gravitates to cooler surfaces

Good Day.

You just don't get it. Most high eff units draw combustion air from the outside, so humidity levels in the home have nothing to do with it. When a furnace is drawing air from the outside it is usually extremely dry air (winter time, its not real humid outside is it?). For that matter, even inside air is quite dry in the winter months. Basically, a high eff unit will create about the same amount of condensation in the secondary heat exchanger whether the combustion intake air is wet or dry.

I don't doubt your expertise, as I have no way to know what they are. As I said, you seem knowledgeable. I do, however not think you know how a high eff furnace works overall. Sure you can Google it all day, but to really learn and know how they work would mean you would have to get into the trade and learn hands on. I have been in the plumbing and heating trade for only 15 years (mind you, that is 15 years of strictly dedicating my time to those trades, not peddling in other handyman duties, but dedicated to what I have made my career out of. Maybe have taken a total of three weeks off in those 15 years, and never worked less than a 40 (usually 50 to 60 and up) hour weeks. So I don't just "play" with this stuff, I LIVE it. and still learn new things all the time (mostly due to how quick things change these days in the trades).

I agree, lets let this thread go. After all, we aren't here to go back and forth amongst ourselves, but to try to help other people with their heating and cooling problems. Have a good one, sir, and on to the next.