More Q&A Spotlight
Houses with very low rates of air leakage and heavily insulated walls and roofs don’t allow much natural ventilation. The whole point of building a high-performance house is to control the source and amount of outdoor air that gets inside.
That’s why designers typically include some kind of mechanical ventilation, often in the form of a heat-recovery or energy-recovery ventilator (HRVs and ERVs). But as LH has discovered, providing fresh air for a very small house can be a little more complicated, particularly when factoring in a clothes dryer that vents to the outdoors.
“When we built our little home (720 sq. ft., basically 2 main rooms) 13 yrs ago, we made it very tight and well insulated, but we did not take into account the need for makeup air,” LH writes in a Q&A post. “The first time we ran our dryer, we had air pulling in through the electrical outlets!”
LH’s solution was to leave windows open a crack, and to install a fan to pull outdoor air into the laundry closet while the dryer was running. Because LH lives in the Pacific Northwest, the fan brings in cold, damp air during the winter.
Although wall and ceiling space is limited, LH wonders whether an ERV is a possible solution. In looking over the options, however, LH finds that advice on this issue seems to be appropriate for larger homes with forced-air heating systems.
“One thing I would like to see on this site is more advice for those with small homes,” LH says. “Everything seems to be geared to having a forced-air furnace, which I don’t have. It wouldn’t make sense in a house this size, and I’ve never cared for the kind of heat they give.”
Ventilation for LH’s very small…
Weekly Newsletter
Get building science and energy efficiency advice, plus special offers, in your inbox.
This article is only available to GBA Prime Members
Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.
Start Free TrialAlready a member? Log in
41 Comments
I have the Whirlpool heat pump dryer, for over a year now.
Clothes come out dry, no wrinkle problems.
On normal its slightly less dry then a conventional dryer, i remember reading a test and they found it got clothes 98% dry while conventional got 99% dry. Not a huge difference and no mold or mildew ever.
Pros:
Saves some energy
No depressurization
Keeps heat indoors in winter.
Cons:
Takes 2-3 hours a load on average, some will be done in 1.5 hours but there is no rhyme or reason, the same load that took 1.5 hours this week will take 2-2.5h next week. Then a month from now it will do it in 1.5 hours again.
Both filters are rather flimsy.
Adds dust to the air and you need to vacuum out the lint frequently
The secondary filter needs cleaning frequently, if its more then partially clogged drying time increases substantially. It recommends cleaning every 5 loads, i recommend every 2-3 and wash the foam core.
Adds heat in summer.
I bought the extended warranty but have not needed it so far.
I'd echo Alan's comments.
My Whirlpool heat pump dryer is only a few months old. No real complaints from me either. Dry times are quite a bit longer for towels & sweatshirts. If you are stuck in the laundry room, it can be noisy. We've changed our laundry patterns a bit to accommodate occasional longer dry times. Rather than "laundry day" over the weekend, we try to do a load in the evenings after work. There are plenty other things to do while the dryer gently dehumidifies the clothes. And the clothes can be put away before going to bed. I can't say I've had any problems with wrinkles yet.
I will say that the laundry room will warm up a touch and be a bit more humid as the dryer is doing its thing. Which, in the winter is actually nice. I'm anticipating a little more run time from the dehumidifier in the basement come summer time though...
I didn't do any scientific measurements but i found no observable humidity increase last summer in the basement, the dehumidifier produced about the same amount of water before and after the new dryer.
And this makes sense, the drier produces liquid water that goes down the drain.
I like the Lunos concept but worry about the noise. They use fairly small fans located in the walls. The noise specs listed on Lunos' website are mostly useless since there are no details about how the measurements are made. I think I would rather go with a larger conventional ERV/HRV unit with the fan(s) located outside and then only run it for 10 minutes every hour or so rather than continuously. The big downside with that are the ducts.
We do use lunos fans in our apartment with one fan being in our bedroom set on low speed (1 of 3) and it’s almost not noticeable. But we do live in Brooklyn with noisy ICE cars looking for parking spots outside 24/7...
Hello
I'll be in a similar situation albeit no dryer. The building will be just 350sqft built with SIPS with two sliding doors. I'm thinking of having a bath fan linked to the shower light to remove bulk humid air while showering, then maybe a very low cfm fan in the bathroom or kitchen/living area that can be on constantly to ventilate the space in addition to a passive vent located behind the small wood burning stove so that any incoming cold air at least picks up some heat from the stove.
This is a holiday cottage so it will not be heavily occupied and it also needs to be a inexpensive. That being said, perhaps just a regular bathroom fan and opening a window a crack when I need to would suffice! Climate 4c.
I have a Blomberg ventless heat-pump dryer. So far so good. No issues. Yes, it takes longer to dry but if you plan laundry duties correctly, you don't have to worry. The clothes don't come out wrinkled or damp, just set it to the extra drying mode and they come out dry. 100% electric home and my electric bill is $55 per month. I even have a heat pump water heater.
If only people had to deal with REAL problems like hanging laundry outside on a clothes line like I did years ago before clothes dryers.
I read through the original thread posted by LH some weeks ago and it prompted me to create my own thread on how to ventilate a very small off-grid house.
I find it odd that so much careful study has been done for this thread (about a grid tied house) in so much that several products are mentioned. methods of installation are analyzed and debated as well as possible long term outcomes and yet for my off-grid home the best advice people could come up with is "crack open a window".
Which of these many options are the most suited for off-grid?
Scott,
Doesn't that make sense for a couple of reasons? The options available to off-grid houses are necessarily limited by the amount of power those houses generate, and the number of off-grid houses is minuscule compared to grid-tied ones.
I can only speak for myself, but being unfamiliar with the power limitations and energy priorities in an off grid house left me unable to make specific recommendations. I suspect that was the case for many. It's not like there was a lack of discussion in the thread.
Scott,
If I remember correctly, I referred you to an article with advice on the topic. If for some reason I failed to do so, here is the link: "How to Design an Off-Grid House."
Here is the relevant advice from that article:
"An HRV or an ERV can use between 300 and 1,300 kWh per year. That’s a lot of electricity — more than most off-grid systems can handle. To ventilate your off-grid home, you have three options:
• Open a window when the indoor air feels stuffy. This is the method I use.
• Install a Panasonic WhisperGreen exhaust fan — for example, the FV-05VK3 (rated at 4.3 watts) — and connect it to a very well-designed duct system. Operate it as little as possible.
• Install a pair of Lunos fans, each rated at 0.14 watts per cfm. One reason that this approach may be appealing to off-grid homeowners: these fans use 12-volt DC motors, obviating the need for an inverter. As with the Panasonic exhaust fan option, I advise off-grid homeowners with Lunos fans to operate the fans as little as possible."
“I think the right way to solve this problem is to actually have the dryer pull the makeup air from outside, heat it, and run it through the clothes, rather than trying to do a closed-loop heat pump system.”
I would love to see someone build this. I also saw it discussed here: https://www.finehomebuilding.com/1993/05/01/dryer-air-intake
My favorite idea of Marc’s: “Using cold outdoor air in the dryer may degrade its drying performance. A solution would be to fabricate a concentric pipe-within-a-pipe to serve as both air inlet and exhaust. The inlet air would be warmed by the exhaust air, like a miniature air-to-air heat exchanger.”
This doesn't address the energy penalty problem. A different hack I've seen on youtube is to leave the intake alone but feed the exhaust through a filter and back into the house. Seemed sketchy to me, but upon reflection is that much different than the condensing option? I guess the volume of air going through the filter is much different, but the filter on my condensing dryer doesn't inspire much confidence.
Trevor,
That's a very bad idea for two reasons: First, the moisture from the clothes ends up inside the house. As we've discussed many time on GBA, tight houses have problems getting rid of humidity. Adding more is not a good idea. And, second, if you have a gas-fired dryer, the exhaust contains the products of combustion including carbon monoxide. This is a good way to kill the family. Even without products of combustion, there can be lots of volatiles cooking off of laundry at high temperatures, including products of chlorine bleach and organics. I prefer to exhaust all of that outside. With a condensing dryer, at least you don't have the moisture and CO issues. If you keep the fragrances and other crap out of the laundry, the volatiles aren't too much of an issue either.
I had never considered doing it myself, so I didn't think through what should have been rather obvious consequences. Thanks for the clarification.
Malcolm, it's not that there are less products suitable for an off-grid home as opposed to a grid tied home that annoys me, it's the implication that ANY product that requires electricity is beyond the capabilities of a solar powered system.
As I noted in my thread, the Province of BC now requires that a ventilation system that runs 24/7 be installed in all new residential construction. I checked if that applies to off-grid construction, and it does. I have no choice but to install one.
I would think in answering my questions about which products are the most energy efficient for off-grid construction people would naturally choose those products for grid-tied construction (who wouldn't want the most energy efficient product?) , but the issue of electrical usage for ventilation devices rarely comes up.
Scott,
You may find these useful:
https://www.ecohome.net/guides/off-grid-and-net-zero-housing/
https://www.ecohome.net/guides/1102/off-grid-living-blog-post-4-appliances-mechanical-and-other-systems/
I'll add another vote for Whirlpool heat pump dryers. We went from an old top loader and conventional electric dryer to a Samsung HE washer and Whirlpool dryer. The dryer makes less noise than the washer, so while it makes noise, it's not excessive. Together the time for a load takes about 30 minutes linger than before, but a load is now about twice as much clothes. It's been a year now and the dryer hasn't given us any problems at all. Cleaning the extra filter 9npy takes a minute or so, not a big deal, especially considering with the increased load size we're still cleaning a filter just as often. I was nervous about this purchase but so far it's met or exceeded all of our expectations.
Electric ventless dryers are the norm in continental Europe, and I've never had any issue with the one I used for 7 years before relocating to the US. When we bought a vented gas dryer 2 years ago, we initially wondered where the condensation tray was and how it could be emptied...
In my experience, clothes (e.g. dress shirts, jeans and khakis, etc.) are wrinkled coming out of either a vented or a ventless dryer, and require ironing.
Another vote for non-vented dryers. We installed a condensing dryer in our PH completed over 5 1/2 years ago and have never had any issue. Numerous residential clients have installed heat pump dryers over the last few years and all seem quite pleased. Recent multi-family projects are all using non-vented dryers as well.
Adding to the Whirlpool heat pump dryer user reports, after about a year of use:
Ours seems to over-dry with very large loads (that fill the 4.3 cu.ft. washer without stuffing). After multiple warranty service calls and replacement of all the sensors and electronics... it's about the same. Recently, I've started using the "Casual" (low heat) cycle with better results.
I've been monitoring energy use for about 18 months and it appears that the heat pump dryer uses about 60% of the energy that the old electric unit did, about what was advertised, IIRC.
One of the techs clued me in on a drying time adjustment for the automatic cycles. It's called "Customer-Focused Dryness Level". Ha. I think that may say something about Whirlpool company culture. Anyway, from the tech manual:
-----
NOTE: If the customer complains about the clothes being less
dry or more dry than desired and the moisture sensor passes
TEST #5: Moisture Sensor, step 2, the total dry time can be
lengthened or shortened by changing the Customer-Focused
Dryness Level from “1” (standard auto cycle) to a “2” (15%
more drying time), “3” (30% more drying time), “4” (15% less
drying time), or “5” (30% less drying time) auto cycle.
1. In standby mode (dryer plugged in but not powered up),
press and hold the DRYNESS LEVEL button for approximately
3 seconds. The dryer will beep and “CF” is displayed followed
by the current dryness setting on the 7-segment display. The
factory default value is “1”.
2. Pressing the dryness level button cycles the dryness setting
between 1, 2, 3, 4, and 5 in that order, starting at the current
setting. The new setting is displayed in the 7-segment display.
3. With the display showing the desired dryness setting, press
the START button to save the drying mode and exit to standby
mode (the START button in this mode does not start a drying
cycle). The result will be stored in EEPROM of the CCU and will
be retained after a power loss
-----
Despite some frustrations, I'd buy it again. Sealing up that dryer vent was so satisfying!
This is incredibly interesting. I usually just let it run a load but last time i needed something early and with 30 or so minutes left (before the cooldown) everything seemed dry so i was going to try less dry next time and see if that gets dry enough but saves energy. I will have to try this after i try that next.
So i used the less dry option, clothes were damp and took about 1 1/2 hours so i will try your method next.
How did you get a hold of the above quote?
I googled around until I found this:
https://s3.amazonaws.com/sm-backend-production-attachments/Job+Aid+-+W10764068+-+Rev+A+(L-88).pdf
It's not my exact model, but appears to be the same in every way I've been able to identify.
Sorry I missed your reply till i went to make this change by rereading your previous post.
Thanks for linking that PDF, i never came across it when i did extensive research when buying my dryer so i owe you one
It worked like a charm, i set it to CF4. Now i will try a load to see if its improved.
Another option to deal with dryer makeup air issue: locate the dryer outside in a covered area. I realize this won't work everywhere, but it works here in NC.
Why do responders keep saying an ERV should be used? It is clear from the manufacturer's info and several responders here that they are not make-up-air units. Indeed, as mentioned, they need to be balanced which means they bring in exactly as much as they exhaust. This is a ridiculous issue that building engineers should have take care of years ago.
As recently as 2011 we built three dwellings here in southern Ontario - no make up air means was called for by building dept (I guess it's just supposed to arrive by magic from somewhere) HRV's and, of course tight construction, were required and the residents suffer for lack of air. I just don't get it - turn on the bathroom fan, have the gas dryer running - THEN have the gas stove on and try to make some utility out of the range hood! Good luck, scary to think about where or what the make-up air might be or be coming from. I can certainly say the smoke detectors tell the truth about what's happening to the air supply!!!
I'm about to start a ~730 SF home in the PNW myself and have been thinking about this issue. I want to add another point that I don't think has quite been hit on - not only is an HRV/ERV (+ Lunos) not designed to provide makeup air but when these devices are thrown out of balance (e.g. more outside air coming in than exhaust air leaving) the heat exchange core will gradually cool down and now your supply air is closer to outside temp ... defeating the whole purpose of the heat recovery.
Now, maybe for the limited amount of time the dryer or range hood is running it doesn't matter that much?
I am leaning towards using a makeup air duct with motorized damper that dumps the cold air right near the mini-split head so it can be re-heated.
Has anyone ever wired one of those dampers to a range hood AND a clothes dryer?
In layman's terms, may I ask for a recommendation for my house: Tiny house on wheels, unvented "hot" roof, built tight....how should I ventilate it? Would a bathroom exhaust fan do the trick? Should I install passive vents in the walls (isn't that just punching fancy holes in my walls? I see tiny house builders doing this but wonder how that affects the tightness of the house). I have no room for ducts, and want my house to be off-grid capable.
We are trying to build it as closely as possible to IRC codes.
I am not a builder, but a DIYer. Thank you in advance for any recommendations.
Eva,
I would install a bathroom fan you can use to exhaust moisture. For makeup air and ventilation I would rely in opening a window. When you do not have a hookup to run the fan the windows can provide both ventilation and exhaust the way they did for every house until very recently. You are building a very small space. It will react quickly to adjusting the ventilation, and the energy penalty will be very small.
The most common-sense response to this question I've ever gotten! Thank you, Malcolm. So you would not recommend putting passive vents in the walls, then? I wonder why so many tiny builders do that.
A passive vent is just a window you can't shut.
I suppose it idiot-proofs the tiny house for those who can't be trusted to open and close things.
For continuous ventilation, I would vent to 20 CFM/person. More during cooking or showering.
I am rather surprised by some of the claims made for the PNW in this article. It depends on where one is located more specifically, but if we are talking about the coastal, Marine 4 zone, I would not want to claim that outside air is drier in absolute or any other terms during a typical cool-season day or night. Temperatures in the lower 40's F. which are also at the dewpoint in mist, or very close to it (i.e., virtually 100% humidity), are routine. In the summer, Seattle can be one of the more humid cities in the US but it isn't felt as readily most of the time because the heat accompanying it is not as intense. Along with Portland and San Francisco, it is in the top-10 cities in average humidity in the US. Do you really want an HRV sucking that into the house without some moderating of it? Probably not, and I would never recommend it to someone. I also agree with others commenting on ERV systems not being appropriate solutions where make-up air is needed unless, of course, one can be deliberately set out of balance without creating other problems to provide a minor excess of incoming air.
While the PNW is consistently damp, the high relative humidity (RH) comes mostly with temperatures below what you would want inside a living space. Using your example, outdoor air at 40°F that is fully saturated, when heated to 70°F it's about 35% RH--right in the comfort zone for humans and structures. Even if that air is only heated to 60°F, it would still be below 50% RH.
If the make-up air device or even the HRV/ERV was heating that incoming air in the way that, say, a forced-air furnace would, that would be true. However, since they are not, and because reality often differs significantly from theory, it is fairly common to have such devices in places like the Northwest overwhelmed by very humid incoming air before there is a chance for it to be warmed sufficiently. https://www.greenbuildingadvisor.com/question/mold-on-erv-intake-side-of-core
I'm on Southern Vancouver Island. Wet winters, but not overly humid in the summer. My experience has been somewhere in between yours and Michael's. I haven't seen problems with either HRVs or unconditioned ventilation since it was mandated in all new houses several years ago. But I've never been able to get indoor humidity below the high 40s by introducing outdoor air. An insulated, heated space without occupant activity adding moisture, like my wife's shed, tracks the RH of our house within a couple of % points.
I would have to disagree with that assessment of the warm season. As I wrote, it simply isn't noticed as readily as in the interior of the US or Canada. https://weather-and-climate.com/average-monthly-Humidity-perc,vancouver,Canada I remember when we used to install "Fresh Air 80" devices in spaces like bedrooms to meet ventilation codes. If the bedroom did not have an exterior wall and pipe of some kind had to be run to supply the fresh air device, one could almost guarantee what the inside of that pipe was going to look like after about 10 years. The issue even shows up above soffit vents into correctly built and ventilated attics in the region, let alone in devices. Sometimes giving equipment southern exposure can help with this significantly in my experience. https://www.pinterest.com/pin/640074165760195467/?nic_v1=1a3pclsMjKfxKujD5Gk%2BgwcGl6URwIPQyuCksJPFtp%2Fa81eLZ86p0m6%2FXNU6cjhX9q
RP,
The average exterior RH may be similar to places like Montreal, but the outside temperature is much cooler in most of the PNW, meaning of course that it is holding less moisture.
I think you are conflating two sources of potential moisture issues. The problems you say you've seen with devices may well be due to high RH, but what occurs in attics and soffits is due to night sky cooling. https://www.rdh.com/wp-content/uploads/2017/08/RCI-2015-Problems-with-and-Solutions-or-Ventilated-Attics-GFINCH.pdf
What's your strategy for ventilating houses in the PNW?
All that night-sky cooling is doing is providing a further mechanism for condensation of the high-humidity air. That type of radiant cooling doesn't just affect roofs and their undersides. It affects metal components, especially, on the sides of buildings, including those which intake for venting structures and equipment as they often have exposed metal wall plates, pipes, and other components. I do not have a solid, proven venting strategy for the NW that avoids these issues. Certain practices like southern exposure help, but I think that is as much as can be said. I am inclined to agree with the OP for whom the article was written that this is not something that has been well-solved for this environment, and the smaller the square footage the more trouble it tends to be due to interior moisture loading adding to the problem. That window being open and shut depending on need and outdoor conditions may still be the smartest venting system yet invented for this area that carries few risks of complications down the road.
RP,
I agree. I'm not greatly enamoured by our choices for ventilation for this climate either. But I think we are way too far along the road of air-tightness to revert back to windows. Shutting them all to control humidity for any length of time will lead to terrible indoor air quality.
Log in or become a member to post a comment.
Sign up Log in