[GEAF]

I have a 10 year old Rheem 90 propane furnace in a rental home. About 8 years ago, the furnace died on the tenants and I called in a repairman and he said it was leaking down the PVC chimney from the roof. There was standing water on top of the furnace, dripping into a small hole into the furnace down onto the burner tray. So I went on the roof and caulked everywhere.

The thick PVC pipe (~6 inches round) goes straight up through the ceiling about 4 feet, with one connection with tight purple glue.

Again, after a cold winter and continuous use of the furnace, it failed again. There is no way the water is coming from the roof, I can only assume it is condensation dripping on the outside of the PVC chimney.

So I did an easy fix. I tied 3 rags on the chimney to collect the dripping water. I've replaced the rags every couple years and have had zero problems since doing that.

I'm thinking of selling the house to the current tenants and would like to find a better fix for this. Any suggestions?

Would making an L connection going out to the side of the house work?

 

[TarheelTerp]

...and he said ... I can only assume

Condensation is a by product of combustion.

Ever see anyone play the trumpet for a while?
The install should have provided a way to deal with getting that accumulating water safely and unobtrusively away.

Luckily... they have an app for that:
http://www.plumbersurplus.com/Brands/Rheem/216?category=Universal+Condensate+Drain|505

 

[diyorpay]

If you have PVC exhaust pipe, you have a high efficiency furnace.

The first cycle waste heat gets routed again thru the heat exchanger, capturing even more heat for your home. The process allows the much cooled exhaust to exit thru plastic pipe. Condensation is a natural part of the process and it mostly exits with the exhaust but some doesn't make it out, especially during and after shutdown process has started. This backs down the PVC (inside) and is supposed to eventually go to a drain.

Sounds like you have PVC that has a weak spot. Poor glue connection? The purple you see is the cleaner solution used on sanded PVC pipe ends before the glue is applied. After glue is applied to ends of pipe to be joined it is common to slightly (and working fast) twist the 2 joined pieces one direction, then back. Then the glue spreads more evenly.

Check your pipe where there are joints. Maybe more glue 'schmeared' on the outside could seal a leak if you see one. Reconfiguring to out a wall would not help per se, but you could correct any weak spots when you re-work the PVC.

 

[Marty S.]

A bad roof seal or a leaking glue joint are your only 2 possibilities.

 

[beenthere]

The older Rheems were suppose to have a drain connection on their air intakes.

 

[GEAF]

Thanks for the advise on the roof leak or leaking glue joint. There is a ~2 foot ceiling to roof gap that I didn't think to check to see if there is a glue joint. I'm betting there is one that wasn't glued properly because of the lack of space for the worker to operation or laziness etc....I'm not sure why they couldn't have used a single length of PVC to avoid these joints. I'll get a ladder up to the ceiling access and take a look.

I agree that it has to be one of these two leaks for the condensation to appear on the OUTSIDE of the PVC pipe. Much appreciated!

 

[techpappy]

Make a flashing around the exhaust where it meets the roof line. Not sure but there may be some available from building/plumbing stores. Properly installed and sealed will stop the condensate from leaking back around the exhaust pipe. Maybe try a roofing company to see what they recommend.

 

[bobinphx]

The combustion condensate is mildly accitic (like lemon juice) It will turn any paper products a dark chocloate brown after a while. This is one way to tell the difference between a roof leak and condensate.

I would suggest attaching a small bit of paper in the area that is wet and see if it changes color over a day or two. no change roof leak or outside of flue condensation. Brown =flue gas condensation. your rags may already tell the story are they brown and crispy from the acid?????


I suspect that your flue is heating and then cooling and the evap of the condensation on the insde of the flue is making the flue colder then the surrounding attic air, thus the condensation on the outside of the flue in the attic. but I am not there!! so I am just guessing. I would suggest that you look into insulating the flue, but I dont know if this is ok or not... I am not a pro... I would check with a pro in your area...

 

[joecaption]

Got a picture so someone can come up with some better ideas?