I spent entirely too much time this afternoon trying to figure out why our furnace wasn’t working. Was it plugged in to the wrong outlet? (No.) Was the fuse blown? (No.) Did the furnace need servicing? (No.) Was the thermostat broken? (No.) Turns out the batteries had died in the thermostat, even though it was displaying its settings just fine.

This all got me thinking, as I spent about an hour climbing up and down a ladder, removing and replacing service panels and whatnot, that our next house should have a heating and cooling system that didn’t need so much maintenance, use so much fuel (gas or electricity), didn’t dry my skin out or drench us in humidity during the summer without actually cooling… okay, a pipe dream? Maybe not.

Then I saw today’s post over at Deliberate Life. Apparently the temperature in the earth, if you dig deep enough, is a steady 50-55 degrees Fahrenheit. In colder climates, people actually put coils of fluid-filled pipes down there in a `closed loop’ system that feeds into their heat pump. That way it only has to raise the indoor temperature twenty degrees because the input temperature is higher than otherwise. How that works exactly I’m not sure, but the same notion applies for cooling too—a much more important consideration here in the oppressively hot Sonoran desert.

In New Mexico at a demonstration straw bale home, air ducts were buried some several feet down in long runs, with an intake vent at one end and outlets within the house (floor vents). They were zoned and there was some way to control the air flow in each room. Anyhoo, the house had a metal roof that would get really, really hot in the summer. A ridge vent allowed hot air to escape, so basically what happened is the air got pulled in from outside, down through the ductwork underground, where it cooled to 55 degrees. It would then get pulled up into the house, cooling the ambient temperature, and get exhausted through the roof. Indoor ambient temperature through the summer for this house rarely got above 80, and usually stayed in the mid- to high-70s, with no supplemental air conditioning whatsoever.

No motors, no electricity, no gas, no water. No appliances to maintain or replace if they break. Just good old convection. Nice.

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