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Crawl-space furnace makes a bad move

Crawl-space furnace makes a bad move

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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 one in our attic space, running new ductwork.

Things seemed to be fine until we had a sustained cold and windy period that 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), but the pipe froze again. I have received many recommendations for fixing the problem, ranging from heating the space to repiping with technology that has the heating element within the pipe. Any suggestions you provide will be appreciated. -- N.J., via e-mail

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, 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, keeping the pipes from freezing and warming 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 2 feet below grade with either fiberglass or rigid insulation. It is not safe to go below the 2-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 that 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 enough to keep the pipes from freezing.

Q: We supplement the heating of our home with a wood-burning stove. To counter the excessive dryness in the house, we use a humidifier. My husband places the humidifier next to the stove, with the moist air blowing at the stove. His theory is that the fan in the humidifier will now be circulating warm, moist air. I contend that the moisture evaporates when it hits the stove. Your comments would be appreciated. Thank you. -- Sparta, N.J., via e-mail

A: You're both right. The stove's heated air absorbs the moisture, the warm air rises to the ceiling, and the fan from the humidifier helps create an air movement that mixes everything. Since moisture seeks its own level, it all evens out in the end, and the relative humidity in the house is increased to provide greater comfort. Even if the humidifier were not aimed at the stove, the moisture it releases in the air will be absorbed. The only suggestion I have is that the fan should not blow the humidified air at the air intake of the stove, as that would result in its being sucked into the stove, where it will be exhausted through the stove pipe to the outside.

Henri de Marne's new book, "About the House" is available at and will be in bookstores by March. Readers can send questions to "First Aid for the Ailing House" to United Media, 200 Madison Ave., 4th Floor, New York, NY 10016, or to Henri de Marne's e-mail address at

Copyright 2007, United Feature Syndicate, Inc. END FIRST AID FOR THE AILING HOUSE 4-6-07.

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