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Here's How To...
Heat a Home

Lots of insulation is certainly the most important key in building a warm house, but thermal mass and solar input can still make a big difference.

One thermal mass system is the thermal rock bed. Air is warmed in a solar panel and blown through a rock bed beneath the house. This is essentially the "forced" air method of solar heat, where the warmth is stored until needed, then blown inside the house.

One of the best ways to use thermal mass is in the form of a radiant floor. A radiant slab is any masonry floor with embedded pipies for hot water heating. Most other heating systems warm only the air, leaving cool surfaces throughout the house that feel like they are sucking the heat away from you. Comparatively, a warm slab underfoot gently releases a steady flow of heat, so the atmosphere feels comfortable even when the air is slightly cooler than normal.

Radiant floors are about the nicest heating systems available, but they fell out of favor decades ago due to problems with the copper piping corroding in the concrete. The leaks were difficult and messy to fix. Today there are many new, long-lasting alternatives to copper, so there is a resurging interest in radiant floor heat.

A radiant heat system can be as simple or as complex as you want it to be. A simple system includes plastic tubing, a few valves, a pump, a source of hot water, and a centralized household thermostat. 

Plastic tubing for radiant floors varies in size from 3/8-inch up to 3/4-inch, but 1/2-inch diameter tubing is the most common.

The most popular types of tubing for radiant systems today are PEX and Entran 3 polyethylene. The latter has three layers for maximum strength, including DuPont plastics and Goodyear rubber, with rayon or aramid mesh for reinforcing. The tubing resists freezing and abrasion, and may be warranted for up to twenty-five years, alhtough realistically it should last much, much longer.

Before a concrete or soil-cement floor is poured, the tubing is laid out in loops spaced no more than 12 inches apart. The length of each run or "zone" should be relatively equal in size. The tubing can be tied to the rebar or wire reinforcing to hold it in place for a concrete pour or temporarily weighted down with large rocks if you are pouring an unreinforced soil cement floor. 

Hot water from a solar panel or tank comes through a "header" made with copper pipe, where the flow is split to each of the zones. Each zone should have its own control valve, preferable a brass ball valve, before connecting to the rubber tubing. The pump is placed at the end of the run where the water is coolest to avoid problems with overheating. A radiant floor with a gas or electric boiler system is controlled by a centralized household thermostat. Typically the boiler has it's own thermostat, so there is always hot water available. The household thermostat turns the pump on to circulate the hot water through the floor. Swing check valves may be needed if the system is cycling water from one floor level to another. 

In a solar heated system the pump can be powered by a photovoltaic panel, without the need for a thermostat. If the sun is shining bright enough to produce hot water in the solar panel, then it is also bright enough to generate the electricity to run the pump that circulates the water through the floor.
Excerpted from Living Homes © 2001 by Thomas J. Elpel with permission from Thomas J. Elpel, HOPS Press, Hollowtop Outdoor Primitive School.

Living Homes takes you through the planning process to design an energy and resource efficient home that won't break the bank. 
Reviewed in The Book Stall.

Living Homes
by Thomas J. Elpel 
HOPS Press, 2001

"I built a house. I botched a lot of things, but it all came out all right. Let me tell you about it."
Radiant In-Floor Heating System
Radiant In-Floor Heating System

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AuthorHouse, 2007

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