I live in North Carolina. We purchased a new construction home. The furnace is a 90% efficiency Lennox. When the nights get too cold, the 3/4" condensation line freezes and (I am told) that the lack of the furnace being able to sense a vacuum in the line, will not let the burner ignite (it is a gas furnace). I saw other postings stating what the code is for NJ .... but what is the code for NC ? Also what are the recommended solutions ? It seems that I could insulate the pipe and when it gets close to the ceiling on the slope, remove the insulation from the ceiling and run it up and over the pipe so that it can take advantage of the ceiling heat. The drain line run is about 30' and then down 9' wall to the outside. Can I just wrap the drain line with heat tape ? The water line heater that I see at ACE hardware indicates on the package "for water lines only... not for use on drain lines"... not sure why. Surely there is a recommended procedure / solution... the development that this house is in has this problem in multiple homes but I want to make sure the H&AC folks fix it correctly and not by the cheapest means. Again, not sure what the NC code is.

Many thanks,
Craig

I don't know the NC code, but my guess is that your furnace is located in an unheated space... like an attic?? And that is the cause for the freezing drain line. Go to one of your local HVAC supply houses and look for a heat tape that is made for DRAIN lines, they do make it. DO NOT USE heat tape made for water lines, where they are full of water ALL the time and will absorb the heat from the tape... to keep the water warm. Use heat tape for drain lines it is made for drains that do not have water in them at all times, and run a much lower temperature. Follow the install directions to the "T"... it will tell you NOT to put insulation over it, and install it right to the end of the pipe to make sure it stays clear of ice.

tsa7man has a good idea but this is a new home and that problem should be addressed by the builder/HVAC company. The work should be performed for free. If not call your local building department because the furnace install instructions probably mention installing in freezing conditions and they can put pressure on the builder.

hvac1000 is RIGHT on with his comment, just make sure that they use the correct heat tape, MAKE them do the repairs. Here in New York state, builders never install 90% furnaces in non heated spaces due to exactly your issue, freezing of condensate. Worse yet is the problems with a power failure, heat tape is dead, and the condensate freezes in the unit and cracks the drain line, trap assemble and collector box. Good luck with your problem...

Thank you for the information about the heat tape... I will check out some other home improvement stores. Yes, I plan on having the builder / HVAC subcontractor fix the problem (for free)... but I wanted to make sure they were fixing it the proper way and not just the cheapest way... and that it was done according to code, etc. By the way, the furnace is in an unheated attic. They have done a couple of quick fixes, but not solved the problem in my mind for the future if we get cold nights in other years, etc. Their quick fixes were things like using the overflow line from the furnace pan for the condensation line, etc. Hence my hesitancy to trust them, since this renders the real drain line useless, does not ensure it does not freeze & burst, etc.. . instead it just gives the furnace condensation another path if the primary path fails.

I have installed 100s of high effiancy furnaces here in New Jersey with out problems. Early on though we did. The first major nono is running of 30 ft across a attic gives you very little pitch for water to flow. We install them so that at most the run may be 15 ft before heading down to the closest bathroom drain or to the basement sump pit,or slop sink.The pvc pipes must be insulated all the way out. However the problem usaully starts from outside when draining on the ground it ices up to the pvc and works its way in.. Being a new home the builder should fix ALL the houses. Quick fix but not to code maybe to tap into the plumbing stack vent in the attic but make sure a trap is installed under the insulation at the pipe so to keep sewer gas seeping into the furnaces evap coil area.unless you have heat tape installed near where it exits the outsidewall this could allway come up. The only solution is to get the condinsate to drain into the house somewheres

The heat tape product that is made for condensate drain lines is by RayChem. Which would be approved by code inspectors, be sure to read the product description / application instructions on the packaging, being that they make a series of heat tape products... SO you are sure to get the right one...

Thank you for these replies. I will contact RayChem and see what I can find.

I have a question about the heat tape on drains statement. My drain is
An iron pipe and I'm wondering how a thermostat controlled heat tape
Could possible overheat on an iron pipe. The heat in the iron pipe should
Trigger the rheostat regardless of whether it is filled with water because of the heat conduction of the iron pipe. I could see it overheating on pvc since pvc doesn't conduct heat like a metal pipe. It seems to me that it should work on empty iron pipe.