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Any good heat recovery options for dryer and range hood exhaust?

Matt Berges | Posted in PassivHaus on

I saw mention of this in another question/answer session, but would like to hear more.
Any way to use Heat Recovery Ventilator for dryer exhaust?-Thanks.

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  1. Riversong | | #1

    No, the lint, moisture and high temperatures require that clothes dryers be exhausted separately to the outdoors. But you can use a condensing dryer without a duct.

    IRC 2003, Section M1501 Clothes Dryer Exhaust

    M1501.1 General. Dryer exhaust systems shall be independent of all other systems, shall convey the moisture to the outdoors, and shall terminate on the outside of the building.

    Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.

  2. jklingel | | #2

    Matt: First, I am not one of the pros here. I've done mental gymnastics over this issue for years, and schemed a variety of "interesting ideas" to siphon off some heat, cheaply and easily, but have never taken the time to try. I just happened to have read this recently, (see link) as I am again thinking about this. My concern w/ a condensing dryer would be the pollutants that I hear (no research on that on my part) come off of our plastic clothes and any "goodies" people through in dryers (scents, anti-statics, etc). For now, I am throwing the heat away and poisoning the neighbors. If anyone has any data on my concerns, lead me to it. john.

  3. Anonymous | | #3

    Would the concerns you have concerning the pollutants be addressed satisfactorily by ducting the HRV so that it extracts from the utility room (or wherever the dryer is) as independently as possible? Perhaps by using a manifold with each extraction duct (with their own backdraft damper) tee-ed into it. This would prevent exhaust from the dryer entering the rest of the house and allow you to recover and re-use the heat.

  4. homedesign | | #4

    this is probably the discussion you were talking about
    but just in case ... here is the link

  5. J Chesnut | | #5

    While I lived in Korea I had a simple washing machine that included a high speed spin dry feature that was similar to the spin dry machines you see at public swimming pools used to quickly dry swimming trunks. This feature takes out most the water and then the clothes air dry within a day or two.

    For tight homes in heating climates this may be a bit risky in terms of introducing too high an amount of moisture that could work its way into the building assembly. Recognizing this some Passivhaus homes in Europe I've heard include a laundry room for air clothes drying that contain an exhaust outlet within the balanced ventilation HRV system.

  6. Lucas Durand | | #6

    Recognizing this some Passivhaus homes in Europe I've heard include a laundry room for air clothes drying that contain an exhaust outlet within the balanced ventilation HRV system.

    I've heard of this. I think I saw a diagram once that showed something that looked like a large-ish closet with dowels running horizontaly across the interior over which you would hang your clothes. I think the diagram also showed an extraction vent to the HRV at the ceiling of the closet...
    In very cold climates, ducting to the HRV might not be neccesary. A drying closet could be built with an open transom over the door. The hot water tank (if there is one) could go inside the drying closet where heat loss from the tank could help dry your clothes. The evaporated moisture would then just be allowed to flow into the house. If the rest of the house is otherwise properly ventilated, the slow release of humidity from the drying closet shuldn't be a problem, should it?
    Sometimes a little extra indoor humidity is very welcome in very cold climates to help prevent bloody noses and split knuckles.

  7. Lucas Durand | | #7

    While I lived in Korea I had a simple washing machine

    Was it an LG?
    When I was in Korea it seemed as though everything from doors and toilets to washing machines and rice-cookers was made by LG... Maybe it was just the apartment building I was staying in.

  8. Riversong | | #8

    Sometimes a little extra indoor humidity is very welcome in very cold climates to help prevent bloody noses and split knuckles.

    Not with a reasonably tight house, which means almost any new house built to today's energy codes. A primary function of whole-house ventilation is to remove the 4-5 gallons per day that a typical family puts into the interior environment through the normal activities of breathing, cooking and bathing.

    A load of clothes from the washing machine can add another half gallon or more of moisture to the air. This is fine in my leaky old cabin, where I hang my laundry on a rack indoors (summer time my laundry goes on a line outside). My indoor RH right now is 27%, so I can afford more moisture. In fact, I have to keep a large canning kettle of water on my woodstove all winter to keep it from getting too dry indoors.

    And, in a tight house, hanging wet clothes in a drying closet will probably result in moldy clothes and a moldy closet unless there is some energy input to assist the drying - either a fan or a heat source or dehumidifier or some combination. Besides, how many Americans are willing to wait two days for their clothes to dry?

    We want it our way and we want it now.

  9. Riversong | | #9

    Speaking of simple washing machines...

    The only washer I ever owned (many years ago) was a wringer washer (what happened to those?).
    You filled the tub manually from a spigot, added detergent and turned on the agitator to wash. Then, when you thought it was done, you drained the water by opening a valve on the bottom and put the items of clothing, one at a time, through an electrically-powered ringer which squeezed almost all the water out of them (while trying not to get your fingers sucked in).

    Then, of course, you hung the laundry on the line in the sun and wind for naturally-disinfected and naturally-bleached and naturally-fluffed clothes.

    When I had a baby 30 years ago, we used cotton diapers and hand washed each one in a galvanized washtub with a washboard and hung them out in the sun - even in winter. That child is a vegetarian to this day - probably because of his lovingly hand-washed diapers ;-)

  10. Lucas Durand | | #10

    And, in a tight house, hanging wet clothes in a drying closet will probably result in moldy clothes and a moldy closet

    Good to know. I have never lived in any kind of tight house. My experience has always been that even when air-drying our clothes inside, indoor humidity is on the uncomfortably-low side in winter.

  11. Lucas Durand | | #11

    When I had a baby 30 years ago, we used cotton diapers...

    Given the amount of extra laundry generated by using re-usable diapers, it seems silly to me to consider doing something other than hang-drying.
    Clothes always smell better when hung out to dry too... unless you live next to a pulp mill maybe...

  12. Riversong | | #12

    Given the amount of extra laundry generated by using re-usable diapers

    This epitomizes the unintended consequences of even "green" options and "good" intentions.

    Some years ago, the late Donella Meadows (Limits to Growth, 1972), wrote an article comparing the ecological impacts of using disposable diapers (plastic manufacture, landfill volume, etc) with cotton diapers (pesticides, water and bleach consumption in laundering, etc) and concluded that it's almost impossible to gauge which were more eco-friendly.

    But her conclusion has been ignored by most of the "enlightened" world: "It's great to try to move our lives in the direction of ecological righteousness, but it's also true that every human activity has environmental impact -- especially the activities of that fraction of the human population rich enough to have diapers of any kind. From the earth's point of view it's not all that important which kind of diapers you use. The important decision was having the baby."

  13. Riversong | | #13

    In a 1999 article, "Never Mind Paper Vs. Plastic Bags. How Did You Get to the Grocery Store?", Donella Meadows summarizes the suggestions of the recently-published book The Consumer's Guide to Effective Environmental Choices by the Union of Concerned Scientists.

    One suggestion on her list is: "Don't buy more house than you need. Smaller homes use less material, cost less to heat and cool and light, store less junk. Every bit of material, warmth, cool, light, and junk comes from the planet, flows to you in a trail of pollution, and eventually goes back to the planet as waste. You're not a bigger person if you own a bigger house; you're just a bigger polluter."

    And she concludes that: "Almost every item on this list not only helps the environment, it also saves money and time and health. Really, the only problem with following UCS's advice is that, if you believe the advertisers, it won't make you admirable, beautiful, ever-young, sexy, powerful, or superior to your neighbors.

    So maybe there should be one more item: Turn off the advertisers."

  14. J Chesnut | | #14

    I don't recall the model of the washer/spin dry appliance I had while in Korea. The Korean economy is dominated by a few very large conglomerate companies LG being one of them. While the appliance I had probably used relatively little electricity it used much more water compared to the newer horizontal access washers now available.

  15. Ma3XGnrBLE | | #15

    Hey, check out ThermalRecycle. we introduced this product a couple of years ago and have documented savings of 50% energy reduction was wwell as 25% reducttion in drying times. this is done using a thermal heat wheel where only the wheel is exposed on both sides of teh unit. exhuast travels through one sdie and teh heat is transfered over the other side where incoming air reclains teh heat. no moisture or lint crosscontaiminates

  16. jklingel | | #16

    Where is the independent evaluation data, and is this a viable residential solution? I'd like to see a product that effectively deals w/ lint and synthetic fumes while recovering energy economically. I am skeptical, but open to proof. Thanks.

  17. wjrobinson | | #17

    Jeff, ThermalRecycle, interesting.

  18. TciwFXAVqU | | #18

    Here is the HE 26...I am still improving it, but I have excellent efficency numbers for under $50.

  19. GBA Editor
    Martin Holladay | | #19

    Mark Montello,
    Basement tinkering at its best...

  20. jinmtvt | | #20

    I have thought about the dryer issue quite alot also.

    results on my tinkering :

    1- get a super fast spinning washing machine ( i've got one..and it works wonder .. Bosch ..1200rpm ...clothes get out only minimally damp can use the spinning twice also )

    2- use a dehumidifier to dry the clothes, and or hang some indoors during winter if your RH% is low enough to afford it

    This is probably the only way to dry efficiently

    hanging clothes outside during summer is pretty efficient also i guess :)

    Sifu Martin : do we have links to dehumidifier closets ?? someone around here has tried that option yet ?

  21. jinmtvt | | #21

    Also. how much heat could really be harvested from a kitchen range ?
    Do you really use it long enough each day to justify a device ??

    Anyone dare to come up with numbers of loss energy$ to kitchen exhaust ?

    We sometimes discuss matters with much efforts but forget that it may not be worth discussing .

  22. GBA Editor
    Martin Holladay | | #22

    Here is a link to an article that discusses drying closets equipped with dehumidifiers: Alternatives to Clothes Dryers.

  23. jinmtvt | | #23

    i became aware of the existence of this and its principles AFTER reading the article you linked!
    But has anyone here try out something similar yet ?

  24. user-1005777 | | #24

    15 years ago, we had a Samsung front load washer with a condensate dryer coil inside. It would wash the clothes, 1100 RPM spin, then dry over several hours. Condensate was pumped out through the drain. It was small and you could not start a second load while the first was drying. We now use a front load washer with high speed spin. Dryer does not run very long to finish off the drying. I don't know why we cannot put an HRV on the output, feeding the supply into the dryer. The problem is economic. Currently my dryer consumes about $16.00 of power a year (10.5 cents a KWHR). I could possibly recover only about $10 of that amount.

  25. user-1102578 | | #25

    Jeff -- ThermalRecycle looks very interesting. . .how do you keep lint from getting caught on the wheel on the exhaust-side and then being blown back into the dryer on the supply-side (when the wheel comes around)? Sucking lint into the elements/burner on the dryer could be risky?

  26. Leonardbugs | | #26


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