How to cut condensation on glass of sliding doors

Q. I live in a condominium with a living room which has three glass sliding doors. On cold days condensation runs down the inside glass. Vents for the electric heating system are high up on the wall opposite the three doors and the fan blows warm air toward the glass.

I cannot keep warm in this place, having formerly lived in a house with radiant hot-water heat in the floor slabs. And I had no condensation in that house. Can you suggest a solution?

A reader

A. The house with the hot-water pipes embedded in the slab involves the radiant principle which heats objects without directly heating the air.

Your condominium heating system involves convection, which is an air-moving process. It is predictable that a radiant-heating system may not trigger condensation on the glass.

Condensation occurs when interior warm moist air contacts cold metal awrP /os at windows and doors. Obviously, the warm air circulated by the blower contacts the glass doors and involves you in the undesirable mopping-up exercise.

If the warm-air outlets can be diverted so as not to play directly onto the glass, you might be able to reduce the condensation, but not by much. A dehumidifier to reduce interior moisture should help some, as would exhaust fans in the kitchen, laundry, and bathroom.

Likely the best solution is to apply a plastic overlay inside the glass. Several companies make such kits. One is Plaskolite Inc., PO Box 1497, Columbus, Ohio 43216. But there are others. The phone number of Plaskolite is (614) 294- 3281. Verify with the company or one of its dealers if its product will indeed reduce the condensation.

Otherwise, is it possible for you to replace the three single-pane, sliding-glass doors with dual- or triple-glazed thermal units? It's expensive, but practical.