Thread: Condensate leak at furnace exhaust

I had a new construction today. 92% condensating furnace in crawl space. My question is right at the furnace exhaust there was a water leak, and about 5 feet away where the PVC pipe turns verticle to go up towards roof another leak. I also checked attic where pipe penetrates roof and it was dry. I could not tell for sure but it looked as if the water was on the outside of pipe not coming from inside of pipe. Any ideas why there could be water in the exhaust pipe. The condensate drain was on other side of furnace going to a pump.

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If you suspect moisture on the outside of the pipe, just hold a sheet of notebook paper against it. You'll see the blue lines blur and form a water spot.

A leak in a Cat. IV vent could be fatal as these are under positive vent pressure. If this is flue gas condensate, it should be very acidic. If there are any drops, you could pat some baking soda to them and see if it fizzies or not. Also, look at the puddles on the concrete floor. Condensate will eat up concrete. Remember your 8th grade chemistry: acid + base > salt + water

A tech needs to inspect this unit and test with a combustion analyzer for CO spillage. With the vent running, you can use gas leak soap bubbles or even Windex or my trusty chemical smoke puffer.

HTH

If I saw the pictures correctly, the pipe does not seem to be glued. Or at least not primed prior to the glue. If this is the case the preasure from the fan may allow the condensate to escape out the fittings. My guess is that the gluing and priming were not done properly muchless at all.

Good job Brian - Good to see some one who call a spade a spade not a world disaster. The PVC pipe is sloped back to and though the furnace to a pump or floor drain. This is in part to prevent the freezing of horizontal pipes in freezing conditions.
Call a qualified HVAC tech and hace him bring his glue and cleaner cans.

Have a GREAT DAY - Brad

It probably is a glue issue but, the reducer used on the exhaust pipe should either be eccentric or placed on the vertical rise to allow condensate to flow back to unit.

Agreed on the glueing and 2 to 3 reducer location. Mechanical code requires pvc primer to be a contrasting color so it can easily be seen if a joint gets missed. Also,+90 furnace mfg instructions always specify that any pvc size change be done in a vertical section of pipe to prevent cond. water from being trapped in the pipe. You guys are correct in your assesment and code and mfg instructions back you up.

Boy am I glad I am back in South Florida where there are no furnaces. Those things were a pain, and added alot of time to an inspection, as oppsed to what I am back doing here. Turn on the heat, wait for the smell of burning lint on the heating element of the air handler...