Recycling the Heat from a Clothes Dryer Vent
Consider your usual clothes dryer, somewhere inside of it is a fan. You know this because hot wet air blows out the back. Quite a lot of air is being blown out of your dryer in this manner, approximately 150 cfm (cubic feet of air per minute). When you consider that this air is around 135 degrees Fahrenheit, it will make sense to you that the heat equivalent of two baseboard heaters is involved.
The heat that the dryer itself puts out is not all of the heat being consumed. The air that the clothes dryer uses originates in the room that your dryer is sitting in: nice, warm air that your heating system has already put a lot of work into warming up. You are wasting that original heating input as well. As that original indoor air is sent outside by your dryer, the same amount of cold outdoor air is working its way back indoors. Every time you run a conventional dryer inside your house, your heating system will have to get busy heating up 150 CFM of cold outdoor air for as long as your clothes dryer is running. That is quite a lot of heating. And, it is in addition to the heat output of the dryer itself. Both electric and gas dryers are guilty of this same sin (electric dryers are even worst wasters overall than gas dryers are but we will look at that later).
Re-directing Hot Air
There are solutions to this problem, the simplest of which is to re-direct the lost hot (damp) air back into the room. If you do try this in well sealed house you will probably not enjoy the outcome. If you live in an older home which has poor weather sealing, however, you may not mind the effect at all. There will be more on this later. This is by far the cheapest manner in which to attempt recycling the heat from a clothes dryer vent. However it is not advisable to do this with a gas powered dryer. The exhaust from a gas powered dryer may not be good for your health.
If you wanted to take this concept a step farther, you could recycle the heat from a clothes dryer vent but still send the moisture out by installing an air-to-air-heat-exchanger. This heat exchanger would be added to the clothes dryer exhaust pipe leading out from the back of the clothes dryer. This is a very low technical, simple solution to our problem. It not only saves the heat that your furnace or heaters added to the room air, but also returns a good portion of the heat that the dryer produced. Truly, this is an elegant solution. But, it does carry a price-tag.
Ventless Clothes Dryer
If you face the difficulty of having no external wall through which you can vent a clothes dryer anyways, you can purchase a ventless clothes dryer. There are a couple of types of dryers that don't require external vents; there are 'condensing' ventless clothes dryers and there are 'heat pump' ventless clothes dryers. In the United States, only the 'Condensing' ventless clothes dryer is available. These dryers are not as complicated as their heat-pump counter parts from Europe which means they are less expensive, lighter, smaller and easier to install. Condensing clothes dryers use a similar amount of energy to dry clothes as conventional dryers use, but, they eliminate the loss of the heat to the outdoors. In this way they contribute to energy savings, at least in the winter time.
Heat pump clothes dryers, on the other hand offer a fifty percent energy savings in the amount of energy that they consume to produce the the heat which drys the clothes. This is because heatpumps operate in an entirely different way than resistance heating coils operate. For this reason, heat pump dryers have gained a certain market in Europe where energy costs are greater.
Have you ever heard of a washer/dryer combo? Well that wasn't just the musings of a frustrated laundry woman. Washer/dryer combos really do exist. The dryer aspect of a washer/dryer functions as a condensing dryer. The washing aspect of the machine uses the same tub. If you are willing to pay the price, you can purchase one in United States. And, the energy savings are the same as are provided by any other ventless clothes dryer.