Radiant heat in floors warms low-level zones

Q. How is the building industry coping with the situation of cold air settling on or near floors? People in sedentary or sitting positions, such as bookkeepers and secretaries, often find the temperature near the floor too cold for comfort. Mrs. Ruth N. Anderson San Francisco

A. One of the advantages of radiant heat embedded in a concrete slab is the resultant warm floor. The installation may be either electric cables or hot-water piping embedded in the concrete.

Floor radiant heat is especially effective in cold areas, but is not as satisfactory in a moderate climate, such as southern California. The reason: Radiant-heated slabs take too long both to heat up and cool down. And, of course , it is either too expensive or impractical to install such a system in an existing slab.

Forced-air heating systems with high supply outlets and low return openings pull the warm air downward. Only a couple of degrees' difference between floor and ceiling air temperatures results.

For maximum warmth near the floor, set the thermostat fan switch at the ''on'' or ''continuous'' slots. Continuous fan operation virtually eliminates cold spots in the rooms.

In existing forced-air heating systems, the nearer one sits to the return-air register, the colder he or she may feel because of the volume of return air flowing to that register. The returning air may be warmish, but the draft makes it feel cool.