Clothes dryer heat recovery systems are designed to save money and the environment by taking advantage of the warm air created by your clothes dyer instead of just letting it escape into the world outside your home. They range from very simple indoor venting systems to more complex heat exchange systems.
The simplest method of dryer heat recovery is to just vent the warm air your dryer creates into your home during cold months to save on your home heating bill instead of directing it outside. Several manufacturers make specialized water filtration systems to take as much lint out of the exhaust as possible before it's released into your home.
Heat Exchange Systems
When a dryer exhausts warm air through its venting system, it must bring in new air to replace the escaping air. The dryer has to use energy to heat this new air in order to use it to dry the clothes. Heat exchange systems use the hot exhaust air that's escaping from the dyer to heat the incoming air. This way the dryer has to expend less energy heating enough air to completely dry every load of laundry. You save money on your utility bill and save the environment by consuming less energy.
Problems Associated with Heat Recovery Systems
Clothes dryer heat recovery systems aren't viable with gas-powered dryers, because the exhaust fumes include carbon monoxide, a colorless odorless gas that can lead to death by suffocation. More than 2000 people die from carbon monoxide poisoning every year in the US. Also, about five pints of water are removed from every load of clothes you dry. This moisture escapes through the ventilation system. If you route the ventilated dryer exhaust back into your house, you are pumping this moisture in with it. If you live in a very dry climate or have a badly insulated house, this probably won't create a problem, but if you live in a damp climate or have a well insulated house that isn't equipped with a mechanical ventilation system, this moisture will be trapped in your house and can cause mold to grow. A good rule of thumb is that if condensation already appears on your windows during cold weather, your house is too well insulated and not well vented enough to pipe moist warm dryer exhaust in without consequences.