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A Little Heat by Harris Hyman, P. E. It's been a good year. We've all been busy designing and building some good houses. Now it's winter. How do we heat them? In 1970, a quality, energy-efficient house consumed about 11 Btu per square foot per degree day (DDay), but today we'd be foolish to be satisfied with a house that used more than 2 Btu. The state of Maine has voluntary standards of about 4.7. A few of us work in the area of 1 (and solar engineer and inventor Norm Saunders has more than a casual acquaintance with 0.0), but most reasonable builders aim for between 2 and 3. Assuming our 1970 house had 2,000