Furnace in attic (High Efficient)

Can a high energy efficent furnace be installed in an attic that is not heated.


One of my inspectors just had a call from a client he did an inspection for last Spring. She said her condensation line freeze and she was told it was against code to install a high efficent furnace in a iun heated area? HELP

Where do you live, Cincinnati, AK? :slight_smile:

I live in Cincinnati

The furnace was a frigidare. I spoke with a compnay here in town and they claim you can install in attics. Anyone know any thing about the brand.

The furnace was a frigidare. I spoke with a compnay here in town and they claim you can install in attics. Anyone know any thing about the brand.


Check your local codes first. I don’t know of any HVAC Manuf. that restricts the installation of H/E condensing type (90%+afue - upflow or horizontal) furnaces in Attics, Crawls or Basements. Installation requirements may differ some, but not drastically.
The freezing of the acidic condensate from the PVC flue vent piping and into the drain is most likely an installation mistake (ie: no slope, sloping the wrong way, blockage or weather ???). Call and HVAC Contractor to check it out.

Thanks for the reply

Freezing condensate should not be an issue if the unit is properly installed.
It is often considered that the flue pipe should slope towards the outside so the water will drain out. This is not the case, it should slope back towards the unit so the condensate can be stored in the furnace where the heat is.

When the furnace is in operation, everything is hot and there should be no problems with freezing condensate.

The drain line should be installed so that there is no reservoirs of standing condensate in the cold space. If traps are necessary, they should be in a location where they won’t freeze.

Very good David. I was just about to post a similar reply.

I see no problem with this install whatsoever.

The following comes from an ICP (Heil) installation manual for condensing gas furnaces: Special precautions MUST be madeif installing furnace in an area which may drop below freezing. This can cause improper operation or damage to the equipment. If the furnace environment has the potential for freezing, the drain trap and drain line must be protected. Use 3 to 6 watt per foot at 115 volt, 40 degree F self regulating shielded and waterproof heat tape. Wrap the drain trap and drain line with the heat tape and secure with ties. Follow the heat tape manufacturers recommendations.

Everyone. Thanks for all the information. This was what I have been trained for for the past 15 years also. It is always good to here back from fellow inspectors. After a while its easy to start second guessing yourself after all these years.

My high efficiency has a water trap. It’s always filled with water, go figure. Is this not needed with an attic installation? Because I can see this quickly freezing.


Condensate is hot. So long as it doesn’t freeze or thaws out when the unit comes back on, it should work.

I had a new high-efficiency furnace installed in my unheated attic and had the same problem of the furnace not running because the condensate trap had ice in it. I didn’t get much help from the GC or the HVAC contractor he hired, so I installed a clamp lamp with a 60 watt bulb to shine on the trap. I also plugged the lamp cord into a $13 thermostat plug from HD that turns the current on at 35 F and laid a cheap thermometer next to the trap. Seems to have solved the problem and when I checked the thermometer reading one night when the outside temperature was 20 F, I saw that the air around the trap was about 50F. Of course now I have a light shining in my attic whenever the outside temperature is low, but maybe I’ll replace the lamp with a short 40 watt heat wire.

I’ve seen a few warnings on the Internet that one should not install a high-efficiency furnace in an attic, but this one I have is a horizontal configuration, and if this is not intended for an attic, I wonder where else it would be used.

A similar problem may exist with HE furnaces in mobile homes, according to this article I should add that not everyone agrees with the Grande Prairie Plumber :slight_smile:

What year was in mandatory / advised for a horizontal attic furnace to be installed in an attic, with an outside releasing overflow pan system ( Calif )?


Just had a heating company tell me no. This is Minnesota.

From Frigidaire/Nordyne installation manual:

Condensate Drain Lines
If the furnace is installed in an area where temperatures
fall below freezing, special precautions must be made
for insulating condensate drain lines that drain to the
outdoors. If condensate freezes in the lines, this will
cause improper operation or damage to the furnace. It
is recommended that all drain lines on the outside of
the residence be wrapped with an industry approved
insulation or material allowed by local code.