1 Helpful?

Frozen condensate overflow line

Down here in Atlanta, I have had two friends call me recently with condensing furnaces that shut off during several days of freezing weather. It seems that the overflow line from the condensate pump taking flue moisture out ran heavily during the cold weather, froze solid at the end outside, causing the pump to back up and the overflow switch turned off the air handler.

Do any of you northern climate folks have a solution for this? One of them doesn't have an interior floor drain to run it to. What's the normal method in the north?

Asked by Carl Seville
Posted Jan 7, 2010 10:34 AM ET


10 Answers

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An indoor drain.

Answered by Martin Holladay
Posted Jan 7, 2010 11:24 AM ET


Kind of what I figured, it just so rarely freezes here that its never come up. Also, condensing furnaces are new enough that we haven't seen a hard freeze since people started installing them.

Answered by Carl Seville
Posted Jan 7, 2010 11:27 AM ET


You are brave to post the question. Up here in Vermont, we watch the TV news, and see Southerners freak out and cancel school when they get just 3 or 4 inches of snow. Then we hear cries of surprise when outdoor plumbing pipes freeze.

So we just shake our heads in wonder, glad that you Southerners are available to provide us with winter amusement.

Answered by Martin Holladay
Posted Jan 7, 2010 11:43 AM ET


Being from NY originally, I find the local response amusing myself. I also found it amusing that two people called me with the same problem within a few days of each other, and that I was able to diagnose it over the phone! Guess I am getting good at what I do.
FYI - they are closing schools at noon today due to a threat of rain, ice, sleet, and maybe snow. Probably nothing will happen.
Glad we can be a source of amusement.

Answered by Carl Seville
Posted Jan 7, 2010 11:47 AM ET


Don't forget to run out and stock up on bread and milk tonight. Fairly obvious solution but a little heat tape and insulation should do the trick. They can just turn it on for the winter and not let it run all year long.

Answered by Danny Kelly
Posted Jan 7, 2010 3:32 PM ET



How 'bout running the exhaust vent down near the condensate drain to keep it warm? ;-)

Or, perhaps a triple concentric flue: intake, exhaust, condensate drain?

Answered by Riversong
Posted Jan 7, 2010 11:08 PM ET


Here in freezing cold North Carolina I just run the condensate line into a 2" PVC line to the outside rather than the conventional 1" PVC. The added size keeps a little bit of ice from being a problem.

Answered by Michael Chandler
Posted Jan 8, 2010 8:21 PM ET


I had the same issue on both my furnaces here in Atlanta. Both condensate lines would freeze. The basement uses a pump so I just drilled into a wet stack (sewage) vent and ran the 3/8" tubing up to there, with proper fitting.

The reason plumbers can't do this is if there is a direct drain into the line. When the furnace runs methane gases can be sucked back into the furnace and blamo! But... a condensate pump line traps the water inside the line and blocks this gas, so you can do it.

For my attic unit, what I did was tap into the drain line about 4 inches up and put in a "T" fitting and the now goes to a condensate pump. This pumps into another wet stack near the roof. The condensate pump will only come on if the outside gravity line freezes. Water will back up but instead of triggering the furnace shut off, it overflows through the new "T" fitting into the condensate pump and voila! It pumps it out ONLY when the drain line is frozen! I added a secondary shutoff if the new pump fails via a float switch. Also added a water alarm inside the drain pan.

I use the attic condensate water to water my garden each year and didn't want to loose that ability. So far it works perfect. We had two weeks of cold here and the pump worked perfect and now since it is had thawed, it now drains to the outside now.

Condensate pumps on Ebay for for $35-50 bucks. Need 3/8" tubing available at Home Depot.

Hope this helps.

Answered by Anonymous
Posted Jan 16, 2010 12:30 PM ET


yeh just happened to me my furnace guy said if, just take the small hose from the pump and stick in in a 2'' pvc pipe elbow facing up glued to a 2'' pvc horozontal pc going thru wall and terminated by an elbow outside facing down the flow will not be enough to fill that so can not freeze shut.
right now i just pulled hose off pump and stuck in bucket .

Answered by Anonymous
Posted Dec 11, 2010 12:09 PM ET


I had the same potential problem, we solved it before the deep freeze by running 1" pvc into the basement where it goes through a trap then into the sewage pipe.

We have a related problem: the exhaust pipe vents just 20 feet above our back patio with a 90' elbow, and then water vapor is condensing on the siding. It works like an ice maker : I have little ice cubes all over the patio.

My hunch is that if we change the 90 degree elbow to 45 degrees and extend it by a couple of inches, it will direct the exhaust away from the house and solve the problem. Is this correct?

Answered by rich cowen
Posted Dec 11, 2010 12:35 PM ET

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