Merits of easier-to-heat dry air vs. better-feeling humid air

Q. In reading columns on home heating and energy efficiency, I have come across two statements that seem contradictory.

One the one hand, it is suggested that home humidity be kept low in winter, taking advantage of dry air's lower heat capacity, to reduce heating costs.

On the other hand, it is suggested that humidity be kept high, since humid air feels warmer.

Of course, other aspects such as plant and human well-being in a dry environment, condensation, humidification cost, etc., complicate the questions. Only from an energy point of view, how is this seeming humidity paradox resolved?

Brian E. Zavitz, Toronto

A. The energy saving by lowering the temperature is 4 percent for every one degree F. drop in temperature.

From Lorne Nelson, senior engineering fellow, Honeywell Inc., Minnetonka, Minn.:

''The energy required for humidification is approximately 1,000 Btu for every pound of water evaporated into the air. For an average home it might be 20,000 Btu per house. The cost of humidification would exceed the energy savings by lowering the temperature.

''If the home was well insulated, the windows and doors were caulked to reduce outside air infiltration, the energy requirement for humidification would be less - in some cases only one-fourth of this average home. In such cases, the energy savings with humidification would be realized.''

From Forrest M. Holly Jr., PhD, associate professor, University of Iowa:

''While it is indeed theoretically more expensive to heat humid air, the additional cost is so small that human and plant comfort are of far greater importance. For the technically minded, at 20 degrees C. the specific heat of air is only 3 percent greater at 100 percent humidity than it is at 0 percent. The energy savings between 20 percent (quite dry) and 80 percent (humid enough for us) would be only about 1.6 percent. Humid air is less dense than dry, requiring less work by the blower in a forced-air heating system.''

From my hiding place here on the lower shelf, all this mere country high school grad type-builder-columnist can say is, ''Whew! Sure is hot in here.''

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