Why are my condensate drains condensating?

[Fyrme]

I have to admit I'm a bit embarrassed to ask this question, but here goes. I have two AC units, both furnaces and evap. coils are mounted in the attic. The condensate drain lines (PVC) are piped over to a near by plumbing drain line. Not only are the two lines from the coil pans dripping on my attic floor, but the P-Trap on the drain line is too. The plywood pretty much is soaked in a 2' radius around the P-trap. Before you ask, it is not a leaking drain, just sweating lines. I technically know why they condensate, but why is this just now becoming a problem? I have owned 5 houses and never had this problem in any of them. The lines also sweat like crazy outside too.

 

[jhelrey]

Are they clogged?

 

[Fyrme]

Negative.

 

[bonneyman]

SWAG - are the p-traps installed correctly? Or doesn't even have P-traps? I have seen - but not common, maybe twice? - PVC condensate lines "sweating" because the traps weren't deep enough, and refrigerated air was being forced out with the water. That will make the lines very cold, and- if the attic air is humid enough - they will sweat.
You should have about a 3" drop (very SWAG) from the inlet side to the outlet side of a P-trap. (That's to make the slug of water heavy enough so air can't be drawn in or blown out). Attic units can hang really close to the joists, and the installers don't give the P-traps enough drop.

 

[Caman]

I'm in agreement with bonneyman. Sounds like a dry trap to me.

 

[mustangacman]

The pvc drains need to be insulated 10' in an unconditioned space.

 

[Rockhead261]

Bonney and Mustang combine for the answer in a mere 5 responses. This forum keeps getting better and better.

 

[BD1]

You may find that your supply duct work will sweat too.

 

[Fyrme]

Thanks guys. The drains coming straight out of the evaporator tray are not P-trapped at all. Just straight PVC into a 1 1/2" common drain that does have a trap. So it may be blowing cooled air through the drains, cooling the water the whole length of the drains. I will try adding a trap at each unit right near the drain exit hole to see if that works.

 

[gungatim]

could also try that foam pipe insulation on them. had to do my cold water pipes for that very reason, when it's humid enough they sweat. the foam just slips on and keeps the humid air from the pipe.

 

[bonneyman]

Thanks guys. The drains coming straight out of the evaporator tray are not P-trapped at all. Just straight PVC into a 1 1/2" common drain that does have a trap. So it may be blowing cooled air through the drains, cooling the water the whole length of the drains. I will try adding a trap at each unit right near the drain exit hole to see if that works.

You could use a pre-made P-trap and pipe it in, or, use one of these.

http://www.rectorseal.com/index.php/ez-trap/

The trap portion is clear PVC so you can see when it's clogged. They include a bendable long brush for clearing it out, and even have a float "kill switch" that will shut off your AC (and let you know!) BEFORE the system overflows and makes a big mess.