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Community and Q&A

PassivHaus Clothes Dryers?

GBA Editor | Posted in PassivHaus on

I would like to learn more about how those building to the PassivHaus airtightness guidelines deal with the clothes dryer.

I did some internet research, but couldn’t find much information on the CFM rating for clothes dryers. I’m assuming they are rated at 200 – 400 CFM, depending on the size the of the dryer. With the current trend toward bigger appliances, perhaps it’s even larger than that . . . I don’t know.

For a house built to 0.5 ACH50Pa, does this throw the system off balance? Do clothes dry? Is there enough air exchange?

I know that you can purchase make-up air kits (ducted valves) for the larger range hoods, and code that requires them above a certain CFM rating . . . but this doesn’t seem like a sensible solution. Maybe we need fresh air intakes for clothes dryers (like they have on woodstoves!).

What about condensing ventless dryers? I found a couple models online that are mfg. by LG. They are available in the US. Reviews are mixed. Anyone have any experience with these?

I guess I won’t even ask about heat pump dryers 😉

Many thanks!

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  1. Anonymous | | #1

    condensing dryer, clothesline or drying closet. we lived in EU for several years, so clothesline is fine for most part. there are apparently people looking at dryers w/ twin wall ducts that are self contained...

  2. Wolfgang Feist | | #2

    In the Kronsberg settlement (1998) we already built in a cabinett in the bathroom with exhaust to the extract air (unheated). That works well during Winter with only latent heat to be delivered by the bathroom heating - and would work well during Summer, too, but a clothesline in Summer is an even better idea. Overall electricity consumption for the circulation fan in the cabinnet was some 75 kWh/a. Not a big deal.

  3. John Brooks | | #3

    Dr Feist,
    Thanks for posting
    I was trying to visualize "the cabinet" and found a photo on page 143 of this document

  4. GBA Editor
    Martin Holladay | | #4

    Thanks for the link. A family with children would need a much bigger cabinet than the one shown in the photo, of course.

  5. Jesse Thompson | | #5

    The Bosch Axxis condensing dryer is a fairly common spec for us in houses without enough make-up air to provide the ~200 CFM the dryer is exhausting:,1249,0,300

  6. Daniel Ernst | | #6

    Thank you all for the very helpful posts.

    I think we can all agree the clothesline is the best option. Even in winter clothes will "freeze dry" if given enough time. But there are times when even the most staunch advocate wants a back-up.

    I guess you could say Dr. Feist's cabinet is a weather protected clothesline with a little active assist.

    The picture of the Kronsberg drying wardrobe was worth a 1,000 words John (and now I have another fine PHI resource to study ;)

    Can anyone comment on the airtightness issue? I don't have any experience with houses in the 200CFM exhaust would cause problems?

    Although a standard clothes dryer would create this condition, I can also imagine a house full of people . . . two 50 CFM bathroom fans and a small range hood (100CFM) could create a similar depressurization. This wouldn't be a problem in the winter. But how much air would the fans move given the resistance (airtightness) of the building enclosure? Does this kind of depressurization create any other problems?

  7. Jesse Thompson | | #7


    Depressurization coming from a strong range hood or a vented clothes dryer can create major problems if there are any combustion devices inside the house (wood stove, fireplace, etc.) due to back-venting. It's why the passivehouse institute has major warnings about including these types of heating appliances in a well air sealed house:

  8. GBA Editor
    Martin Holladay | | #8

    A comment on Jesse's post: potential backdrafting problems can occur with atmospherically vented combustion appliances, including woodstoves and fireplaces.

    The use of sealed-combustion appliances, however, should protect the occupants from the worst effects of depressurization.

  9. Wolfgang Feist | | #9

    Well, the exhaust from the cabinet is running directly into the exctract air of the HRV system. The whole system might be (it's not necessary!) forced to a somewhat higher massflow during the time you need that high air masses, but still balanced - with 80 to 90% heat recovery this does not matter too much. In the projects we normally have in a 4 persons home some 100 m³/h (which is perfect for IAQ) most of the time (60 cfm - when will you change to scientific units?) with a possibility to increase to "party ventilation" with some 160 to 200 m³/h (still balanced). If you sometimes want even higher mass flow - say in a 30 persons party e.g. - you can still open windows and that might be a good idea with 4 kW of extra internal loads! The experience is good - if you run higher ventilation, you would have problems with too low air humidity in most European climates in Winter. Martin, how do you use dryers in the US? Most of the owners in Kronsberg have 4 persons in the family and were satttisfied with their drying cabinet. Hoever, what you have to take into account: It takes some 8 to 12 hours, as long as you do not heat the cabinet, what would increase energy demand for drying significantly. Yes, clothsline is the most efficient solution and yes, in most climates it even works during Winter (but slowly), my mother always used that. Well, it's looked at in a kind of "out of fashion". Did you know that in Germany cloth dryers are the third highest consumers after heating and domestic hot water? Dish washers and washings mashines, even fridges ar quite efficient nowadays. But condensing dryers do have a quite high consumption - unless you use a heatpump, there are 2 models available doing so.

  10. Wolfgang Feist | | #10

    Martin: Yes, sealed combustion with separate air intake is the solution for combustion devices. These are a good idea anyhow (avoiding CO backdraft what might be really dangerous and even can occur in untight buildings). Even small woodstoves are available in Europe - sealed and with separate intake. We have had whole working group developing solutions for "heating with wood" in a passive house (Protokollband Nr. 36).

  11. GBA Editor
    Martin Holladay | | #11

    To answer your question, most Americans no longer use clotheslines. They throw all of their clothes from the washer straight into the dryer, which operates on natural gas, propane, or electricity. These 125 cfm to 200 cfm appliances do not come with any provision for makeup air, but the backdrafting risk is small due to the fact that most U.S. homes are leaky.

    My two kids are both teenagers, and the drying closet shown in the photo that John Brooks linked to is not large enough to hang up even a single load of laundry. In our family, we do two loads of laundry on some days.

    I lived for many years without a dryer. In the summer, a clothes line; in the winter, a wooden rack indoors. Now, with older kids, I use a propane dryer much of the time, although I still dry all of my bluejeans on an indoor rack.

  12. Wolfgang Feist | | #12

    Martin: Yes, I often asked myself whether one can top the German extensive use of the wash-dry-wear-cyclus. You just told me: Yes, one can. But, doesn't matter, with a cabinet a bit larger than the one shown, you can do what you need (:-). And another idea: The propan/butan heaters in your dryers - these will produce some 1 to 3 kW of heat output. That is just as much you need for the whole heating of a passive house. So, you could save the money for the whole heating system and use the dryer exhaust air (run it through the HRV) to heat a Passive House. You might laugh: Such ideas have already been tested by one of the "extremist" passive house engineers in Europe.

  13. John Brooks | | #13

    Our American homes are larger, our cars are larger, even our refrigerators and washing machines are larger.
    Should we wash our clothes once (or twice)a day (drying overnight) or once a week?
    Is Bigger better?
    Should we have ginourmous dishwashers and wash our dishes once a month?

  14. Wolfgang Feist | | #14

    John: Well, I think, these are questions, you may answer for yourself. It does not matter very much - if you feel more satisfied with that "style of living", it's your choice. But what is not just your choice, is, how much of the earths ressources you claim, how much CO2 you emit, how much radioactive waste you leave for your children. These problems do not force you to change the style of living - but to reflect, whether you might be able to increase efficiency and to change to sustainable ressorces. Both is possible, it has been shown by innovative pioneers (like Harald Orr and William Shurcliff). So, there is no need to go on with the unssustainable path. The Passive House accepts even big floor areas - it accepts even big drying cabinets, there is heat recovery! - even a big freezer can be super-efficinet and require only a few kWhs each year. I guess, the world will accept a somewhat excessive lifestyle - as long, as this does not endanger the human species.

  15. Daniel Ernst | | #15

    Dr. Feist: Thank you for the data and commentary. For a better understanding of the American perspective on laundry, you might read this article. It sums the present situation:

    Restrictions on hanging laundry in the US is usually confined to "subdivisions" and communities that are attempting to market their location as having a "higher class." It goes hand in hand with those subdivisions that have minimum square footage requirements for new homes (i.e. no less than 2500 sq. ft. - sorry for the unscientific units ;)

    We're only a couple of generations removed from hanging our laundry. Cheap energy has led us to a more convenient lifestyle. We (and I know it applies to me) sometimes confuse convenience with progress. These things will change.

    I'm glad to see your working group is considering woodburning appliances. For those of us living in the country - with a ready supply of firewood - we cannot ignore such a cheap and renewable form of energy - or the psychological benefit of a well built fire.

  16. Wolfgang Feist | | #16

    Daniel: Yes, I agree with all your statements. This is, why we concentrated on efficiency - so, there is no need to go backwards to a less convenient style of living. But, we all might learn, that riding a bicycle is not unconvenient - but healthy (:-). And, that there are things more important than convenience - like a talk with a good friend or to play the violin.

  17. Erik Haugsjaa | | #17

    Can someone comment on this strategy:
    Using a standard electric dryer (non-condensing) and running the exhaust thru a "lint trap" device like this, rather than exhausting outside?
    Deflecto Lint Trap (other similar products also linked at that page...)
    My idea would be to use this sort of thing along for "almost dry clothes" coming out of a front-load washing machine and then have a standalone dehumidifier running in the laundry room.
    The Bosch Axxis seems nice, but it's very expensive.

  18. user-659915 | | #18

    The pdf link supplied by John Brooks (response #3 above) is extremely instructive: appreciation to the design team for providing an English-language version of this detailed information. Note that in addition to providing drying cabinets in each unit the designers specifically warn against the use of exhaust-air clothes dryers in the homeowners instruction manual (p. 43).
    Other useful takeaways: multifamily design to spread engineering, detailing, and district-heating and other infrastructure costs: row-house format to significantly reduce external wall area: the need for an informed and cooperative occupancy to ensure design performance is met.

    For those struggling with US/metric dimensional comparisons here are some simple rules of thumb: 1 sq. m. is about ten s.f.; 100 mm is about 4"; 300 mm is about one foot. I can offer no such easy translation of U-value to R-value I'm afraid.

  19. GBA Editor
    Martin Holladay | | #19

    Here are the conversion factors:
    To convert a European U-factor to North American units, divide by 5.678. (It's easy to remember, because the digits are consecutive.)

    To covert a North American U-factor to European units, multiply by 5.678.

    R-value is simply the inverse of the North American U-factor, so R=1/U and U=1/R.

  20. user-659915 | | #20

    Thanks Martin, that's a pretty easy number to bear in mind.

  21. John Brooks | | #21

    Translation TIP
    James, I have found many interesting links on non-english sites
    It is very easy to use a Google translator .... works very well
    when using the translator.....
    the grammer can be very amusing ;-)

  22. Wolfgang Feist | | #22

    The Kronsberg project (that's the one cited above by John and James) was the leading Passive House settlement in the so called CEPHEUS project: . The monitoring was sponsored by the EU. There are lot`s of papers available, most were published in German, but some also in English. With this project wide spread application of Passive Houses began in Germany and Austria, followed some years later by most of the other European countries. Now details for passive house construction are available for all types of buildings. Good sources are also the proceedings of the Passive House conferences, which have been translated to English since 2006: . A Remark to the conversion of R-Values: I just kept in mind, that R 1 is almost that of a single pane - which has an U-Value of some 5.6 W/(m²K) in SI units. Funny: The physics is the same, but you can easily make it look different.

  23. John Brooks | | #23

    here is a good Translation example:
    compare this translated portal:

    to the limited English "version"

    there is much more info in the google "tranzilated" version

    Dr Feist you are fantastic.

  24. John Brooks | | #24

    "not the insulation save"
    I love the non-filtered grammer it adds something to the message.

  25. user-659915 | | #25

    So Martin, do you have a handy-dandy litres/100km to mpg converter too?

  26. Daniel Ernst | | #26

    Here's one of my favorite conversion programs. It's shareware:

  27. GBA Editor
    Martin Holladay | | #27

    There are plenty of good metric conversion Web sites available. Here's the one I usually use:

    1 liter = 0.264 gallon
    3.7859 liters = 1 gallon
    1 km = 0.6214 mile
    1 mpg = 0.425 km/liter

  28. Wolfgang Feist | | #28

    John on google translator: Yes, that machine is geting better and better. But: You still need to be an expert on the topic, to really understand, what is meant. And: you are right, there are still parts of the "public passive house course" which have so far not been "officially" translated. You might guess, that I do not like to use just the GoogleTran"z"lator :). So, everybody is welcome to proofread some of the so far not translated pages. Everybody will be mentioned on the page, who did. Let's get this information available for anybody, who wans it.

  29. Daniel Ernst | | #29

    Erik - Here's a British Wiki link that has information on using a dehumidifier to dry your laundry:

  30. Erik Haugsjaa | | #30

    Daniel, thanks... nice link! This is going one step further and eliminating the dryer. So it's basically replacing the HRV from the Feist-type drying closet and instead using a standalone dehumidifier. Should work fine, I'd expect.

    I'll probably try both and report back. Tumble dryers are of course what people (myself included) and they are easier to just toss clothes into, but on the other hand, some things can end up more wrinkled than by line drying if you are not right there to get the load when it finishes, so I suppose there are pros and cons to each. And line drying (even if inside with a dehumidifier) has got to be cheaper than tumbling.

    When we lived in Switzerland for 3 years, our apartment building had a huge "drying room" with clothesline filling the room and a huge heater called a "tornado" or something to that effect. I should try to dig up a photo.

  31. Wolfgang Feist | | #31

    Daniel: The dehumidifier-drying-cabinet. Yeah! That's it. It's so good to see the physics work again. Most services can be done without or just with a little bit of energy - if we just use the laws of physics and not "brute force".

  32. Erik Haugsjaa | | #32

    BtW Daniel, you end your original question by saying "I guess I won't even ask about heat pump dryers ;)"

    But a dehumidifier IS a heat pump, so there you go!

  33. Riversong | | #33

    Now that John Brooks has linked a current thread to this old one, which I hadn't read, I feel a need to comment.

    WOLFGANG FEIST said: much of the earths ressources you claim, how much CO2 you emit, how much radioactive waste you leave for your children. These problems do not force you to change the style of living - but to reflect, whether you might be able to increase efficiency and to change to sustainable ressorces. Both is possible...I guess, the world will accept a somewhat excessive lifestyle - as long, as this does not endanger the human species.

    This is exactly the mindset that has created all of our current global crises and will drive us to extinction (along with half the species on earth) if we do not radically renovate our paradigm.

    This current paradigm states that:
    The way we live is the best (and only) way to live.
    The way we live relies on constant scientific and technological progress.
    The problems we create along the way can be resolved by more and better of the same.

    This closed circular thinking is a form of either stupidity or insanity (or both).

    We CANNOT have both infinitely greater convenience AND sustainability. We CANNOT sustain the current lifestyle of the "developed" (sic) nations, let along bring the rest of the world up to this level. Not only is this patently absurd simply in ecological terms of living on a finite planet with an exponentially-growing human population, but ignores the fact that wealth shared by some, in our economic system, requires poverty shared by billions. There are equity and social justice issues as well that cannot be ameliorated let alone solved by more technological efficiency.

    But the mindset that believes that if tight houses are good tighter houses are necessarily better, is the same mindset that blindly accepts that the answer to our technogenic problems is more technology.

  34. Anonymous | | #34

    Robert... just because the world population has grown exponentially...


    You are much smarter. Post as such.

  35. Riversong | | #35

    And just because the sun has always risen in the morning does not mean it will rise tomorrow.

    But the best predictions are that the sun will come up tomorrow and that there will be a continued increase of human biomass, with the global population expected to reach between 8 and 10.5 billion in the year 2050.

  36. Anonymous | | #36

    Population trends are per country moving from exponential to less than such to topped out to declining. You know that Robert. That means decades old exponential data is no being assessed with a bit of intellectual power. More like a third grader know it all kind of thinking. And to compare that to the life cycle of the sun per its daily rise and fall... is less than kindergartener's intellect.

  37. jklingel | | #37

    Anonymous: I have no recent numbers, but only old ones and a fair understanding of people. World populations are going to increase. "ZPG" (zero population growth) was pushed in the 70's, but had pretty much died away without any significant impact. People are going to continue to have sex regardless of the consequences. Certain religions (M and C come to mind) are going to push having kids for various reasons (bottom line: make more of X religion types). Etc. Sure, "past performance is no indication of future performance", but this is not financing; this is human biology. Now; we need to get back to the topic. j

  38. user-917907 | | #39

    Here's a Wikipedia link to their article on Drying Cabinets.

    And here is a link to an American-made drying cabinet.

  39. user-871583 | | #40

    Not sure if too late to past, but would like to get back to the subject of the post. Dryers.

    If a 'traditional' dryer is put through some good lint filters, is there any reason the ducting could not be linked to the HRV in order to recover some of the heat?

    Do they move enough air to depressurize a dwelling (do they need make up air in a .5ACH50 house)?

  40. user-917907 | | #41

    Here's a British Wiki link that has information on using a dehumidifier to dry your laundry:

    For those who tried unsuccessfully to follow this link, here is the correct one:

  41. kevin_in_denver | | #42

    Answer to Sean Wiens:

    Direct linking to a conventional HRV might not be quite practical. A dryer is moving 250 cfm, and the house ventilation requirement might be a lot less than that. In fact, if the dryer is on when no people are home, the ventilation requirement is zero.

    But I'm glad you're starting to brainstorm some improvements!

    I think one goal is to eliminate the dryer's need for holes in the home's envelope. There are products out there designed for this that impinge the dryer outlet air on a little pool of water. The water does a good job of hanging onto the lint in the air stream, but unfortunately doesn't reduce the humidity of the air stream. NOTE- gas dryers must always be vented to the outside.

    Of course, the building science of not venting a dryer would suggest potential mold problems due to condensation of excess moisture. But what if you could dehumidify the room very quickly and let the moisture just drain out the floor drain or the washer discharge pipe?

  42. user-871583 | | #43

    Since it does not appear that there are 'sealed' dryers on the market yet, how about making our own. Put a conventional dryer in a sealed cabinet that has a passive make up air vent to the outdoors. That way, it can pull as much air as it needs and the exhaust air will not be drawing form the home and removing previously conditioned air. Like Martin, I do not feel a drying closet is very practical for North America. When I do laundry I do about 3-5 loads at a time. Sheets, Towels, Clothes. Now I only do this every two weeks or so but if I had to use a drying closet, it would mean I had to do laundry much more often and much smaller loads. This is a less efficient use of water and electricity. The washer is generally going to use the same power regardless if it is doing a small load or a large load. Same with the dryer, a large load does not use a lot more electricity than a small load. As long as you do not over pack the dryer and their is good air flow, all sizes of loads use pretty much the same power. So the use of a drying closet would actually increase the electrical needs for the washer. And if you are having to run a dehumidifier all the time for days to do 3-5 loads, is that really less electricity compared to running the dryer on med or low?

  43. kevin_in_denver | | #44

    Sean, The answer to your last question is buried in a parallel thread:

    Comment #29, if correct, indicates that a dehumidifier uses half the energy of a dryer.

  44. jackofalltrades777 | | #45

    LG now makes a condensing electric NON-venting dryer. Some people don't like them because it takes twice as long to dry the clothes as a conventional vented dryer but that is the compromise one has to make in order to not have it vent.

    There is an "answer" to the dilemma on what to do with poking a hole in a wall and having a dryer pull out conditioned air. The answer is a VENTLESS electric condensing dryer. They are energy efficient but there are some drawbacks. Longer drying times and smaller capacities. Don't expect to run a load of laundry for a family of six on these types of dryers. As the saying goes, the less holes in ones building envelope, the better.

  45. GBA Editor
    Martin Holladay | | #46

    Peter L,
    Your suggestion (in Comment #47 of this long, old thread) is exactly the same suggestion provided in Comment #1, back in May 2010: a condensing dryer.

    I have written extensively on condensing clothes dryers, as well as several other clothes-drying options. Here is the link to my article: Alternatives to Clothes Dryers.

  46. jackofalltrades777 | | #47


    Oops, I didn't notice that the thread was an old resurrected thread from three years ago. I currently have a standard vented dryer and if the outside temps are 30F, the aluminum dryer vent pipe is 30F and the inside of the dryer is around 40F (once you open the door). There is some serious thermal bridging going on with the steel vent pipe and some serious air leakage since the exterior flapper door on the vent almost never works properly. Then there is the air exchange happening with the dryer on. A lot of conditioned air is being funneled out that vent pipe. With all of that being said, do you believe a condensing non-vented dryer would NOT be the better choice? It seems to me that a vented dryer is basically a 4-6" hole in your wall.

  47. GBA Editor
    Martin Holladay | | #48

    The least expensive way to address your problem is to install an exterior termination with a better seal. This is the model that most people choose:

    It's also available from other suppliers:

    Condensing dryers work, but they are expensive and they dry clothes slowly. If you can afford one and you are willing to accept the limitations of this type of appliance, you can certainly buy one if you want.

  48. LenMinNJ | | #49

    [Note: We ended buying an LG condensing dryer and are very happy with the decision.]

    In our new all-electric (no combustion devices) Passivhaus, the only non-ERV breach of the air exchange barrier and thermal envelope is the clothes dryer's exhaust. We wanted that convenience. We weren't willing to live with a condensing dryer.

    Since the dryer exhausts to the exterior of the house, I suppose the makeup air will have to come in via the ERV intake, which will be at the exterior temperature.

    The laundry room (like the bathrooms) only has an ERV air intake. So the outside air brought in by the dryer's de-pressurization will have to travel through the house to the laundry room, changing the temperature of the house: reducing it in Winter and raising it in Summer.

    Since the dryer exhausts directly to the exterior, the heat in the dryer's air exhaust will not be reclaimed by the ERV in Winter. We'll lose that energy.

    So it seems that in Winter, running the dryer will cool off the house, and running it in Summer will heat the house.

    Then the two ductless mini-splits will have to compensate to bring the house temperature back to where we want it.

    It we provided an exterior air intake to the laundry room and sealed the room to the rest of the house, the makeup air wouldn't have to come from the ERV. But then the laundry room would be outside the thermal envelope of the house, and would have to be insulated like an exterior wall. Not a great idea!

    It doesn't seem like there's a good solution to this problem other than to place the clothes dryer outside the house's air barrier and thermal envelope, or to accept the change in temperature while the dryer is operating.

    Does anyone have any ideas?

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