Last winter the condensation from our high efficiency furnace caused our line to freeze from the floor drain where the water was running into, all the way to the septic. No one was there to flush toilets or run water more than the drips that comes from the furnace. It was below 0 for several days prior to that.

Where do you suggest we run the water from the furnace instead of the floor drain?

The furnace is in the basement and not near an outside wall.

2 Answers 2


If the furnace was running in the home and the temperature in the home was above about 50 degrees F. I can not see how the drain line could freeze. Also, how did the drain line freeze all the way into the septic tank? Drain lines that are underground do not usually freeze. I believe that more information is needed as to the construction of your home, the location of this drain line, and the overall operating conditions need to be explained farther. Is there a vent line between the house and septic tank that would allow cold air to enter the drain line at that point and freeze that drain line? Also, 45 degrees is probably a little to low a temperature to maintain a home when you are away. I would keep mine at 55 degrees.

  • 1
    A lot of septics can be close to frost line.And a little leak will freeze and line can freeze solid. Happens when not much snow to blanket soil.
    – user101687
    Jun 18, 2019 at 22:32
  • The heat is at 45. The house was built 5 years ago. No one comes in and runs water so a slow steady drip over a couple of months. First time this has happened since it was built.
    – Julie J
    Jun 18, 2019 at 22:37
  • So do you think it freezes from the septic line back to the condensate line? So when the house is unoccupied not enough warm water is going into the septic system to keep it thawed. The small flow from the condensing furnace is just the right amount to freeze in the septic line? It could be that in the winter when you are gone you will have to collect the condensate water in a tank in the basement. Alternatively, you could try to heat the condensate water before it goes into the septic line high enough (say 150 deg F) that the septic line would stay unfrozen. Jun 19, 2019 at 2:29
  • I do not see that helping at all. The boiler is at 180 already and the small amount of warm water that goes into the cold line does not drain fast enough.and freezes . Hot water freezes first. And you need to add the pump to get it out of septic line.
    – user101687
    Jun 19, 2019 at 10:20

They make condensing water pumps. And you pipe it out doors only 3/4 or 1 inch pipe needed. Have it come out so not in snow and check from time to time. to make sure cleared.

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