Sagging or missing sections of insulation should be repaired, as they not only waste energy but may also indicate a leaking pipe in need of repair. If the insulation is worn because it covers a pipeline in a heavy-use or travel area, the insulation should be replaced, then covered with a sheet-metal jacket to prevent damage in the future.
Heat flows in direct proportion to the temperature difference: the hotter the water in a pipe (or the colder the ambient temperature in the environs), the more heat flows. Likewise with a house: for a given inside temperature of 70 F, three times more heat flows when it’s 10 F outside than when it’s 90 F.
Now imagine 140 F water in pipes going through the carport in the winter and 0 F outside. If those pipes were under the house in a crawl space, even when it’s 0 F outside, the crawl space is much warmer (some heat from the heated floor above + average ground temperature of perhaps 30 F) even when the’s ventilation because the under-house temperature tracks more closely ground temperature than the outside ambient.
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Excerpted from Going Green, available as an eBook at this list of eBook retailers online.