clothes dryer heat recovery

This easily built project recovers warm moist air from a clothes dryer that would otherwise be exhausted to the sub-zero outside.

Energy is saved two ways: heat used to dry clothes remains in the house and less cold air is drawn in by preventing negative pressure. Electrical energy that is used to dry clothes contributes to house warming. Moisture that is added to the house air is welcome during a northern winter when the cold temperature outside causes the air in the house to become very dry.

I only use this in winter. In the summer, I re-route the vent to the outside but I use the clothes dryer only on rainy days. I use the outdoor clothes line whenever possible. I also have a indoor clothes line which is used on damp days and even in the winter.

My clothes dryer is used as little as possible as it uses an enormous amount of electrical energy. The nameplate on mine lists 25 amps at 240 volts or (25x240=) 6000 watts. When I do use it, it is good to know that the expensive heat is used twice by not being blown outside.

I made a simple box of scrap wood with a slot in one side to insert and remove a standard furnace air filter. The size of the box is determined by the size of the furnace filter. In my case, I used the same filters as my heating furnace so the inside dimensions of the box are 20x20 inches by about four inches deep. The slot is 1 inch wide to accommodate the filter. See the video below for more details.

The box has wood battens inside along three sides to guide and support the filter. On the side opposite the slot, facing downward, a right angle 4 inch heater duct fitting is attached to feed air from the dryer into the box.

The box has a plywood back and is attached to the wall above the dryer with two wood screws. Heated moist air comes into the box through a flexible aluminum pipe attached to the duct and exits through the filter into the room.

The entire box is primed and painted with ordinary house latex (water based) paint for moisture protection.

Installation involved removing the existing aluminum flex hose from the wall and attaching it to the duct on the bottom of the box.

I then filled the existing exhaust hole through the wall with fiberglass insulation.

As I did this I thought about what a heat loss this hole represented with it's aluminum tube to the outside wall. Another benefit of the project is to effectively seal up this leak to the outside for the winter.

This is the existing flex and rigid pipe as removed from the dryer after re-attachment to the bottom duct of the heat recovery box instead of to the outside vent. The dryer was then plugged in and the hose attached before sliding it into place.

Some of you with larger families who live in climates with warm, damp winters may prefer an approach using a heat exchanger to remove the moisture from the air before it is released into the house. Here are two approaches: one by Gary Reysa at builditsolar and another by ALK Engineering. I think that you will agree that these are quite a bit more complex than the my simple approach but as I said, I welcome the moisture and don't have very much of it. I can tell if I have excess moisture easily when I see condensation on the windows in the same room. With one load at full heat with -15C outside, the moisture from the clothes dryer dissipates throughout the house and does not normally condense on the cold window.

You can buy commercial heat recovery units at the Home Centers like this one from Jafine.

Simple, like mine, this is a plastic box with a diverter valve and a nylon sock to catch the lint. I have used one of these in another home and it does work.

It's a pretty cheap product though and messy to clean. I spent less money on my home made project. I think mine looks and works better and will probably last longer.

Please watch this video showing some views of my project.



Thank you for your interest.

George Plhak
Lion's Head, Ontario, Canada

Update June 20 2019:

What it looks like when the filter gets changed.

The old filter slides out the side. A bit of work with a vacuum cleaner to clean up the box. This is after about a year.

Carry the filter outside as gently as you can to not disturb all the fluff.

Amazing how much lint is caught even after the lint filter in the appliance. Normally this would be vented outside or clogged in the outlet pipe.

I fold them over an put in the garbage. I don't think these are recyclable?