IDEA: Dehumidifying Clothes Dryer

This would be a short post, but I've realized that some people don't know how a dryer or a dehumidifier actually work. So, real quick – a dryer passes air over wet clothes, the moisture evaporates and is carried away by the air, warmer air can hold more moisture, so a hotter dryer setting will dry things faster. A dehumidifier passes air over a cooled coil where the water will condense (like on the side of a drinking glass) and is then pumped away.

Here's what bugs me about clothes dryers – they heat up the air, remove some moisture from the clothes, and then pump that air out of the house. It seems a lot like turning on your furnace and then opening up all the doors and windows in your house, it just wastes energy. Also, since the pressure in a house will always try to equalize itself with the outdoors, outside air will sneak in (through window/door cracks) at the same rate as the air being pumped out by the dryer.

My idea is to put a dehumidifying unit inside a dryer. This way air can be heated up and recirculated within the dryer. The only thing that will leave the dryer will be the condensing water, which would be pumped to a drain. This idea would only work with electric dryers though, since a gas dryer has to vent the fumes out of the house, otherwise bad things happen to you.

I'm not sure of the efficiency of dehumidifiers, or the cost to run them, but if people leave them running in basements it can't be too horrible. Plus, it seems like it'd be very hard to be less efficient than heating up a bunch of air and then pumping all of that heat outside. This dryer/dehumidifier setup would also probably be a lot more efficient than your standard basement dehumidifier for two reasons – 1) it's a small enclosed area and 2) the air it's removing the humidity from has been heated up and has more water to pull out of it than normal room temperature air.

Someone build one of these, and make it affordable. I'm thinking of making a small unit that can be retrofitted onto an existing (electric) dryer.

And while we're on the topic of efficient clothes drying.. I've just started running the dryer less, and then hanging the slightly damp clothes to finish air drying. If I'm going to be using an inefficient beast of a machine to dry my clothes, I might as well use it less. (The clothes from my last couple of batches that I dried like this are also less wrinkly.)

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  1. Ricerckt93 said,

    You must not be aware of the device that attaches inline of your exhaust pipe.

    It is a box like structure that has a movable flap inside. This flap can be manually moved to suit your needs.

    If it is 90 degrees out side you can exhaust all that damp moist air to the outside.

    Or, is it is only 20 degrees outside, flip the switch, it will redirect the air back into the house.

    Now these are normally installed on hard ducting, but depending on the setup of your exhaust you may be able to attach it to flexible ducting.

    February 1, 2009 @ 5:18 pm

  2. Medlam said,

    I think you'll find, if you investigate dehumidifiers a little further, that they are the *exact opposite* of a clothes dryer. One heats up air so that it can absorb moisture, while the other cools it down so that moisture will condense out of it. Running both in the same machine would probably be far less efficient (and effective!) than just venting the hot air outside.

    You *can* buy (not that I've been able to find them anywhere) an apparatus that you can insert into your drier exhaust vent to redirect the flow indoors during the winter, and switch it back during the summer. That should save some energy for you, if you can find one.

    February 1, 2009 @ 6:24 pm

  3. Helena said,

    Consider line drying most of the way and then tumble dry for the last moisture. Just about no wrinkles this way!

    February 1, 2009 @ 6:44 pm

  4. sparx said,

    Wow. Someone must have stumbled this article recently, because it's gotten over 800 more hits today than its normal 0-3!

    I am aware of them, and have seen them installed on flexible ducting. The intent of my "dehumidifying dryer" idea was to have a completely closed system, avoiding pumping heat outside or into the house, and definitely avoiding pumping moisture into the house (which is a problem with the device that you mention.)

    February 1, 2009 @ 8:02 pm

  5. sparx said,

    I wouldn't consider the humidifier the exact opposite of the dryer. In fact, if you look at it again, you might even say that it completes the drying cycle. The water is removed from the close using heated air, and then removed from that heated air through condensation.

    Its efficiently is going to be dependent on what is being used as the "cold source". For example, if cold water on its way to a water heater was used as the "cold source", you would actually be reclaiming the "waste" heat from the dryer and saving money on water heating – the savings would be minimal, but keep in mind that you've also avoided the problem of dumping heat outside, and the problem of increasing the inside temperature along with the inside humidity.

    February 1, 2009 @ 8:09 pm

  6. sparx said,

    I would love to line dry. Unfortunately, in my current apartment renting situation, I'm unable to do it. 🙁

    February 1, 2009 @ 8:11 pm

  7. Ricerckt93 said,

    Sorry, don't know of any device at this time that can do that for you. As for pumping warm moist air back into the house really isn't a problem here. During winter months it is EXTREMELY dry in the house. The added moisture isn't a problem but helps as a relief.

    Well, good luck to you. Someone must have come across something that may help you.

    February 1, 2009 @ 9:36 pm

  8. anon said,


    This is a cute idea, but there are several problems:

    1) The dryer will be working hard to heat up air, and then cool it down with coils (yes, most of the energy will go to cooling the air, not the water in the air, since there ir more air than water)

    2) Dehumidifiers are painfully slow at removing water, it will take much longer (2-3 times) to dry a load

    If you don't mind the extra wait, you can achieve the same effect by line drying indoors, while running several dehumidifiers, or an industrial one.

    February 1, 2009 @ 9:46 pm

  9. sparx said,

    Except… the dryer wouldn't be the source of the cold, so it wouldn't work any harder with the cooling. Yes, by recirculating the air it would take longer to remove the moisture this way, but the goal of the idea is efficiency (recapturing and reusing waste heat), not speed.

    February 1, 2009 @ 10:04 pm

  10. Michael said,

    LG make an all in one wahser drier that uses a dehumidifier for drying. There are two sizes. The larger size is model number WM3987HW. There are 2 problems with this, it costs $1600 and it takes 5 hours to run a clothes load. I am planning on building a dehumidifier drier. I will let you know when I have time.

    October 28, 2013 @ 3:40 pm

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