Published on September 14th, 2014 | by Henri


Pipes freeze after furnace is moved from crawl space

Q.  My wife and I recently bought a small ranch that had an old, inefficient furnace in the crawl space. During the fall, we disconnected the old furnace and decided to install a new furnace in our attic space and run new ductwork. Things seemed to be fine until we had a sustained cold and windy period which froze our water pipes. We did not take into consideration that the old furnace in the crawl space was emanating enough heat to warm the space and keep the pipes from freezing.

I purchased an electric heat tape and fiberglass insulation, and applied it to the area that I believe to be most susceptible to the freezing (along the foundation wall running almost the full length of the house). We again went through a cold spell and the pipes froze, despite the heat tape.

I have received many recommendations for fixing the problem ranging from heating the space to re-piping with technology that has the heating element within the pipe. Any suggestions you may provide will be appreciated.

A.    It was a mistake to put the new furnace in the attic. The heat it generates will cause snow on the roof to melt, thus causing ice dams to build up at the eaves. This can result in leakage inside the walls, wet attic insulation and damage to wall and ceiling finishes. There is also a loss of efficiency as the furnace is in a cold space that is presumably ventilated; any benefit from the furnace’s stand-by losses is lost. If the furnace had been left in the crawl space, its stand-by losses would warm the crawl space, keep the pipes from freezing, and warm the first floor.

Since it is unlikely that you will go to the expense of returning the furnace to the crawl space, and if the insulating you have done is not as described below, I suggest that your first step be to seal any cracks admitting cold air anywhere around the foundation; this will keep the wind out. You should caulk them.

If there are any vents in the foundation, please close them and place insulation over them. If you haven’t done so, this is how the crawl space should be insulated: put R-19 fiberglass between the band joists with a vapor retarder facing inside the crawl space; insulate the walls down to two feet below grade with either fiberglass or rigid insulation.

It is not safe to go below the two-foot level as it could result in walls cracking under the influence of deeper-penetrating frost. This should prevent further freezing of the pipes that are surely just under the first floor joists, as the earth’s warmth and the heat loss from the first floor should keep them above the freezing point.

You should also insulate the water pipes with neoprene insulation you can buy in hardware or building supply stores; they are easy to install. However, if you have already insulated as described above, and insulated the pipes, you may need to provide a modicum of heat. I know of old stone cellars in which pipes used to freeze until a simple 100 watt light bulb was kept on during cold weather and proved to be sufficient to keep the pipes from freezing.

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