Every time you use your clothes dryer, you are producing about 20,000 Btus of heat, then throwing them all outdoors through the outside vent. You could be using them to heat your home. Instead, you are wasting them. That's not all you are wasting. You are also venting warm air from inside your home -- air you have paid to heat -- and throwing that away too.

It can amount to some 4,000 cubic feet per load, or about half the air in a typical home.

That's still not all. You are also throwing away a lot of humidity -- humidity your home can probably use during the winter when central heating has dried your air to levels commonly found on a desert.

Keeping that humidity in your home would make your home more comfortable. You would feel warmer at lower thermostat settings, and furniture would be less prone to shrinkage or cracking.

What's the solution to all this waste? Indoor dryer venting. It's a simple matter of rigging your dryer so it doesn't vent outdoors. Of course you don't want indoor venting during the summer. Then it would overheat your home and make it unbearably humid. But during the winter, indoor venting is an idea whose time has come.

How do you go about it? There are several kits for indoor venting now on the market. The simplest is little more than a box fitted with a fitting for your dryer's vent hose, plus a furance filter to take lint out of the exhaust air so it won't blow around your home. Come winter you unhook your dryer hose from the outdoor vent and attach it to the fitting on the bottom of the indoor vent. It's as simple as that.

Some more sophisticated types have a system of dampers inside so you can switch from indoor to outdoor venting and back by flipping a lever. Others include small fans to eliminate the slight back pressure caused by the filter.

For a long time, dryer makers have been opposed to the idea of indoor venting. They felt that the damp air from the vent would recirculate through the fryer and increase drying times. They were also worried about backpressures from the filter, lint in the air, and the possibility that the hot exhaust air might prevent the proper cooling of the dryer motor.

It now seems that all these worries are minor if you observe a few precautions.

First, make sure any venting kit you buy has a good filtration system. Most use ordinary furance filters. You can increase filtration by switching to a special high-performance filter.

Second, make sure you mount the indoor vent above the dryer. This helps keep the hot exhaust air away from the dryer intake to prevent the problems of overheating and extended drying times.

Third, make sure you clean or replace the filter on a regular basis. Replacement filters are cheap, so replacing makes more sense than cleaning.

Where can you get indoor venting kits? They are available at hardware stores, home centers and so on. If you can't find any in your area, here are the addresses of some of the makers:

Universal Products, 165 Skyview, Vandalia, Ohio; Bede Industries, 1985 West 85th Street, Cleveland, Ohio 55102; Heat Handlers, Box 105, Addison, Illinois 60101; In-O-Vent, 7295 Cascade Woods Drive, Grand Rapids, Michigan 49506.

One last thing: Before you buy any indoor vent, make sure it is approved for your use on your type of dryer.