My Mother's House Part IV: Installing a Passive Heating System

In this stage of building MOTHER's house, workers install a geothermal heating system. Read how it's done and what suggestions we have for a heat-exchanger system of your own.

| January/February 1982

With winter upon us, the Eco-Village crew has been hard at work getting "My MOTHER's House" ready to weather the coming storms. Beyond the innumerable seasonal details to be taken care of — which include installing insulation, sealing, shingling and flashing to name a few — we've had to finish off one component that we really won't be needing all that much until next summer.

Because our building's single most important energy-conserving feature is its earth berming (and, on the front half of the structure, the sod roof), we've been anxious to get on with the necessary backfilling and grading. But, to do so, we've also had to go ahead and install the natural cooling system (it consists of a pair of buried 15-inch-diameter, 60-foot-long plastic pipes), through which ground-cooled air can be drawn into the house. Now air conditioning may not be at the top of your list of concerns as the snow blows past the living room window, but the tubes had to be installed before the berming could be done. So snuggle up to your wood stove while we tell you about our passive home cooling system. 

Using the Earth For Passive Heat


Because soil is far less willing to conduct heat than is air, the temperature of the earth below the frost line remains comparatively constant throughout the year. At 25 feet down there's essentially no change in the ground temperature, although at shallower depths the tempering effect is weaker. In general, however, the earth six feet or more below the surface will stay fairly close to the average annual air temperature for the area.

That stability of ground temperature is, as many of you know, the key to the energy efficiency of earth-sheltered homes. The soil surrounding such structures is likely to remain in the 50 degree Fahrenheit to low 60 degree Fahrenheit range — so the buildings lose less warmth in the winter and gain less heat in the summer, than they would if their walls were exposed to outside air.

However, earth sheltering doesn't eliminate the need to exchange a home's interior air at least once every two hours. (Such a change is required to maintain adequate oxygen in a house and to prevent the accumulation of carbon dioxide and toxins emitted by gas appliances, wood stoves and the building materials themselves.) You may be surprised to know that, in a very well-insulated dwelling, the task of heating or cooling the "new" air to room temperature can account for a substantial portion of the building's thermal requirements.

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