Should you vent your clothes dryer inside your house?

Q My sister-in-law told me about a device she attached to her dryer vent that collects the lint and directs the air into the house instead of outside. She says it saves a lot of energy on heating and keeps the house from getting so dry in the winter. I'm thinking about getting one. Is this a good idea?

A: This is an idea that's been around for awhile. Back in the 1970s, I often advised my clients to vent their dryers into the house during winter. My reasoning was just what your sister-in-law says: save all of the heat from blowing outside, and use the moisture to help prevent excessive dryness in the house. I suggested tying a stocking to the end of the pipe to prevent lint from blowing all over the house.

Dryers are significant users of energy. They suck air from the house into the dryer, heat it up with an electric element or gas burner, and blow the hot air — along with the moisture from your clothes — out the vent pipe. All of the heat produced by the dryer is "lost" when you blow it outside.

Any time you exhaust air from your house, an equal amount will be sucked in to make up for it. This "make-up" air will come in through every available hole and crack in the house, mixing with the air you've already heated or cooled and causing your furnace, air conditioner or heat pump to work even harder.

In the summer, the air sucked in by the dryer tends to be hot and humid, making the air conditioner work harder. In the winter, the make-up air the dryer sucks in tends to be dry, making the air in your house dry. If your house is already very leaky and dry in the winter, this will just make it worse. Some people try to counteract the dryness by installing a humidifier to add moisture to the house. But the wisest ones (in my opinion) will spend that money sealing the house, making it less dry in the winter while reducing heating bills.

All in all, dryers can cost a lot to operate and create serious issues with moisture, comfort and even health.

So does it make sense to bypass all of this and re-route the dryer vent to the inside? Important note: Do not consider this if you have a gas dryer. The exhaust vent is also the combustion vent. You don't want the products of combustion (e.g., carbon monoxide) in your house.

If you have an electric dryer, there may be some houses during some times of the year where using this strategy could be beneficial. The problem is determining which houses and when. How do you know when the added moisture will make you more comfortable or lead to mold growth or even rot? This depends on a number of factors including how tight your house is, how big it is, what it's made of, how much laundry you do and what the weather is. For most of us, trying to keep track of all of that to decide whether to vent the dryer inside or outside is probably more trouble than it's worth.

There are some new, high tech solutions to this. Europeans have been using condensing dryers for a number of years. They don't exhaust air at all, so the problems associated with conventional dryers are eliminated. They tend to be smaller than most Americans are used to and take longer to dry the clothes, but otherwise seem to work well.

The latest high tech approach is the solar clothes dryer. I don't believe there are any tax credits for it yet, but it definitely shows promise. You take a special cord called a "clothes line" and stretch it between two poles outside in the sun. I've seen some research reports that there are even some special devices now available to pin the clothes to the line. This approach is experimental and highly controversial. It's even illegal in some communities. But if you really want to save energy on clothes drying, it may be worth looking in to.