THE OWNER BUILT HOME & HOMESTEAD
(Page 14 of 15)
January/February 1971
By Ken Kern
About twenty-five years ago someone had the bright idea of installing a fan in the bottom of the heater. The resulting "forced-air" system allowed for smaller ducts and more freedom in design. Moreover, it was possible to keep the house and furnace on the same level. The majority of new homes are equipped with warm-air perimeter-duct or baseboard heaters—this in spite of the fact that extensive research proves convected-air heating is generally unhealthful—for heating appliance manufacturers and installation contractors are about 10 years behind research developments in their field.
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Since the best method of domestic heating may be a wise combina tion of radiative and convective systems, I mention two more promising "combination" systems. From a centrally located furnace, hot air is blown down into radiating feeder ducts imbedded in the concrete slab. Hot air circulating through these feeder ducts heats the floor surface to a temperature of about 73° F. as it passes through to a larger perimeter duct and then into the room. Thereupon a blanket of warm air passes up the exterior wall where it is most needed. Since the floor surface is heated, no cold air floor register is necessary. The absence of cold air at the floor level also contributes to the "living zone" comfort.
Crawl space perimeter heating is another recently developed "combination" system. It is said to produce the most uniform temperature with the quickest response at the lowest cost. In this system the total crawl space serves as the plenum. The central down-flow furnace supplies warm air to a short, stubbed-out duct system, pointing to the far corners of the house. Registers are located around the outside perimeter of the rooms. Return air is collected in an interior wall and returned to the furnace through a short duct. When a layer of heated air exists below the floor joists, not only is the floor surface temperature increased, but also the "living zone" temperatures are made more uniform from floor to breath level.
No matter what type of heating system one chooses, if the house is not adequately insulated and weatherstripped, heating costs will be excessive. In cold climates it will cost only half as much to heat a well insulated building as a poorly insulated one. The Housing and Home Finance Agency (Release No. 126, Oct., 1949) reports that the annual fuel saving from moderate insulation of a typical dwelling in Washington, D.C. will amortize the additional cost-expense in two years! In one carefully planned experiment it was shown that coating the walls and ceiling of an experimental room with aluminum paper reduced the heating load by 21%.
It has also been found that 80% of the hourly heat loss from a concrete slab or crawl space house is through the perimeter and floor, with only 20% through the ceiling. And of this total heat loss, most occurs along the perimeter rather than downward through the floor. In two houses in Champaign, III., the one not weather-proofed required 3,000 gallons of oil in one year, whereas the same-sized house with storm sash and doors, weatherstripping of outside doors, and insulation of ceiling and sidewalk took only 800 gallons.
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