Q. We had an addition put on our home in 1994 that extended our kitchen and added a three-season room to the back of our house. Under the addition is a crawl space (I know your feelings about crawl spaces) that is only under the kitchen eating area. The re is an open space under the enclosed porch. Would it be possible and practical to move our dryer vent from exiting the house to move the heated air under this crawl space to warm the floor and possibly reduce our heating bill? The space involved is ab out 12 feet by 15 feet and three feet deep. There is a flexible duct that extends through the crawl space to the rear wall to a floor register. There is no access to this space, only two vents on either end, one facing west the other east. The addition is on the south side of the house. Would this solve a problem or only create more than any possible benefits?

A. Now that we have been put on notice that our energy costs will be going through the roof, as if we couldn’t already see that, I certainly understand why everyone wants to squeeze every tiny bit of value out of whatever they do when it comes to energy conservation. Some things make intuitive sense and heating up air hot enough to dry wet clothes in an enclosed tumbling drum-- a dryer-- then venting the heated air out of the house seems to many to be somewhat wasteful. Why not keep some of that heat? Pick up a load of laundry fresh from the washer and weigh it or just heft it to feel the weight. Dry it then weigh it again. The difference in weight is the weight of the water the dryer removed. Remember a pint of water weighs a pound.

Home centers sell these little plastic boxes into which you put water to collect lint then hook the dryer hose to it. The theory is the hot-- now lint-free-- air will fill the laundry room with dryer heat and you get the proverbial two birds with one st one: dry clothes and free room heat. But the dryer air is very moist and there’s where the trouble can start.

There is a section in the building code that requires dryers to be vented to the exterior. Some may consider that chilly, vented, void space under your new room exterior space since it’s not heated or cooled and via the foundation vents is aerodynamical ly connected with the outside air. I’m not one of them. Exhaust vents designed to be vented to the exterior should do exactly that.

If you pump wash water heated to the point of vapor by the dryer into a cold space, much of it will condense back to liquid and cause-- potentially-- all sorts of problems and some may not be immediately apparent. Not to mention depositing lint that gets past the dryer’s filter. I’ve seen crawl spaces where for reasons of pure laziness dryer vents have been directed and along with the molds and mildew I see large quantities of lint. A nasty latent fire hazard.

The worst I’ve ever seen was a behind a false wall in a basement build-out where the homeowners were complaining of a chronically moldy basement family room. I peeked behind the wall under the the floor of the first floor laundry room and saw a pile of lint easily five feet deep directly under the dryer vent hose that terminated just under the floor. This had been going on for years. I was amazed as were the unsuspecting homeowners. The moisture problem was then on its way to being solved.

Your crawl space should be insulated up under and between the floor joists. Peek in through one of those foundation vents to see. Your builder should have left an access to this area-- at least two concrete blocks tall and two blocks wide-- so someone, If they had to, could slither in there to do whatever may have to be done. You best bet for the crawl is to insulate and insulate some more.

I don’t recommend running your dryer vent into that crawl space-- ever. If you want to use one of those little plastic interior vent boxes, promise you’ll only use it from November through March when the inside house air is bone dry and direct the moist dryer exhaust to the exterior the rest of the time. And don’t tell anybody I told you it was OK to do even that.