Directing a dryer vent into the interior space in the winter to reduce heating costs?
canada_deck
| Posted in General Questions on
I came across this product being sold today. Isn’t this a generally bad idea?
This was being sold in climate zone 5. Is there a climate zone where it would be a good idea?
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I've seen this product before. In fact, we had the same question at FHB and had it answered by an expert. The short answer is that it's not the heat that is important to vent outside the house (well, maybe it is the heat in the summer when you are running your AC), but it is the moisture in the dryer exhaust air that needs to be vented outside whether you are in a heating, cooling, or transitional time of year. If you want to read more about this, here's a link to the Q&A I mentioned:
https://www.finehomebuilding.com/2010/11/11/tapping-into-a-dryer-vent-for-heating
Since that link is behind a paywall, I'm not sure what the total response was. Yes, humidity is a big factor, and adding that much humidity to most houses is not a good thing. But more immediately important is that many dryers are gas-fired and the exhaust also contains the products of combustion. Diverting the dryer exhaust into the house can kill a family quickly via carbon monoxide poisoning. These diverters are never a good idea.
OTOH, the new apartment style condensing dryers are not bad. They require no venting (no holes in the envelope!), and condense the laundry moisture and send the condensate to a drain. All of the heat generated by the dryer is vented into the building, but they generate quite a bit less heat than conventional dryers.
Good points Peter. Seems like I keep hearing positive feedback on condensing dryers.
Brian
It isn't just heat that comes out of dryer vents. There is a large amount of cloth fibre (lint) that I wouldn't want in my interior air.
I have an electric dryer and I am installing an interior dryer vent. The interior vent will be on a wall very close to a second option, an external vent that will be used only showing the summer. Here is a photo of the setup so far.
The vent is a FUNMAS dryer vent and it cost $60 on Amazon.
We will wait 'til April to cut a new home for the external dryer vent.
richmass62,
Except for heat pump dryers, the IRC requires that dryer air be exhausted to the outdoors, and all ducts terminate outside the building. See M1502.2, and M1502.3.
Malcolm, I can see why it is in the code, but this seems like an area where the code is almost never enforced. For example the code says "dryer exhaust ducts shall have a smooth interior finish" but 95% of the vents I have seen have a rough corrugated metal finish.
I would argue that an interior vent is a great way to go during times when you have extremely dry conditions, if you take the steps necessary to do it safely. Of course the first rule is not to do it with a gas dryer and my install checks that box.
The benefits, besides avoiding the depressurization of my house (higher heating bill), is that my first load of clothes raised the humidity of the indoor air downstairs from 40 percent to 50 percent. This is a health benefit, given that the forecast tomorrow is for even lower humidity levels.
My recommendations if you want to do this are:
1) Make sure your dryer room is completely air sealed on the outside walls, and open to your home's interior, so that the moist air will exit into your main living space where it is beneficial in the winter. (Our laundry room has no door.)
2) Make sure your walls and windows have a high R factor and high U factor so they don't become surface that will "rain" when you do your laundry. (In our case we are upgrading the windows from U 0.3 to 0.23 and we just upgraded the effective insulation of the walls on the laundry room from about R8 to R28.) Also if you run your dryer in the hours after the sun has hit your wall from the outside there the condensation is reduced (though it may not be necessary to worry about time of day if your insulation is sufficient).
3) Slow down the dry cycle and the rate of moisture exhausted by using a lower drying temperature (this makes clothes last longer anyway and is often seen as a benefit of heat pump dryers).
4) Use laundry detergents that don't contain bad chemicals (need more research on this one, but I read that it can be an issue with some brands)
5) If your dryer vent filter is not set up with a water trap to catch everything, like microplastics, consider drying your synthetics "plastic" material clothes with your dryer vent set to exhaust to the outside. This is something I will likely pursue, but to do it I need to set up a "y" in my ducting to switch quickly back and forth between interior and exterior venting.
6) Get a cheap humidity meter to install next to your dryer, and avoid using the indoor vent frequently on damp days. In my case I also found that with a large load of mostly cotton clothes, it helps to "time dry" your clothes for 30 minutes, take a 15 break, and then set the dryer on auto to finish your load. I realize this slows down the drying operation but it is still a lot faster than using one of the newer Miele heat pump dryers.
We will go to a heat pump dryer eventually, when they get a bit larger, but for now this seems like a very "green" solution for us.
Even in places where building codes aren't enforced (or exist at all), they are a heavily vetted baseline of "the worst house you can legally build." Not that there aren't areas in the code that need to be updated, or that "the worst house you can legally build" is a bad house.
Venting a dryer to the interior is a terrible idea, no exceptions. I don't have time to go into all of the reasons why right now but suffice to say, for anyone else reading this, do not do it! Mold and fire are real risks unless you pay extremely close attention, and inhaling the micro-plastics emitted from modern clothing materials is not good for your health. My family and many neighbors are dealing with PFAS poisoning, which is still relatively unknown but you'll hear more about it as information spreads.
Isn't it amazing that we are talking about the clothes we wear next to our body or wrap our children in; and have to worry about micro plastics and PFAS poisoning! Not to mention a few other common chemicals used in clothing......:(
Yes. It seems to make more sense to get rid of your PFAS clothes than have to worry about what comes out of your dryer. Fortunately the US PIRG organization has a campaign to get the companies to remove the PFAS from their clothes. They said that LL Bean clothes were particularly bad, believe it or not...
https://www.boston.com/news/environment/2022/04/06/clothing-brands-stopped-using-pfas-us-pirg-report/
richmass62,
I don't think it make any difference how well you do the work. Starting with the premise that we can avoid the requirements of building codes, or the liability concerns that come for doing that, is simply a bad idea.
Two kinds of issues here. Some building codes are more critical than others and as I stated in the post I am constructing a vent outside in addition to the indoor vent, in order to comply with code.
Some of my family members have health issues that surface when the air is too dry so the idea of using the dryer moisture seems to make a lot of sense. Just as our heat pump water heater gives us free dehumidification in the damp basement, the dryer vent could give us free humidification in the house during the coldest winter months.
I think I am not the only one here who really wants to cut down on electricity usage to combat global warming. Keep in mind that the insulation, fire stopping, fire proofing work is leading to a house that will be way beyond code when we are done.
The issues of microplastic pollution are important but I would argue that filtering this stuff is the best approach rather than simply exhausting it to the outside where it will get into rivers eventually. I welcome suggestions on how to properly filter it, or how to avoid producing it in the first place. I think that by running the dryer at lower temps I am actually producing less microplastic "emissions" than when I send all the exhaust outdoors and run the dryer on high.
richmass62,
"Some building codes are more critical than others"
I agree. Things like not using the proprietary tape on a WRB, or slightly missing your fastener schedule on drywall aren't things I'd lose sleep about. Whereas having too low a guard on a landing, or over-spanning a beam are errors of a different category. The distinction I would make is that serious ones a) might compromise the building in a way that would lead to damage, or b) are safety issues. I'd definitely put using that indoor vent in the second category.
Another related issue is that while individuals might decide they are willing to consciously disregard code and take the consequences of that, it's another thing to advocate that as a viable approach, and suggest it's a good idea to others.
We've been using a full size Whirlpool Heat pump dryer now for about 8 years. It's worked extremely well for the family. Not sure what the issue is with heat pump dryer vs size as Whirlpool is still selling them in the 7.5 cubit foot range.
My issue with redirecting electric dryer exhaust (tried it for a few months when we had one) was the sudden elevation in humidity combined with very cold outside temps. This resulted in condensation and mould on cooler basement walls/floor. The target for the house is 37-40% RH at these cold temps.
Other than a few hours taken to pull the dryer housing and clean evaporator/condenser (after eight years of use) , the heat pump dryer has been 100% reliable and effective. You do need to spend an extra minute or two after each load to clean up lint filters.
Thanks for the info on that dryer. I checked it out and for a $1800 dryer the reviews are not great. I don't think the market has matured on these yet and we will eventually get one, but: isn't the microplastics issue the same for heat pump dryers vented indoors as for regular heat dryers?
There's heat pump dryers but also non heat pump condensing dryers (perhaps more reliable).
I think both are much more of a closed circuit in regards to air flow. Nothing like the pass through of a conventional vented dryer.
Perhaps you could find some way to filter your conventional dryer, but why? For "health" is an oxymoronic answer imo. I suspect most dryers would struggle with any sort of significant filtration resistance. I would rewrite your 5 point bullet list as:
1)Properly vent your dryer
2) Air seal your house to reduce humidity loss
3) possibly run a little humidifier if absolutely needed (there may be risks doing this as well depending on specifics, but fewer risks than the dryer option and a heck of a lot more control)
Question: do you know what level of tightness is necessary, in terms of ACH units, to make a significant dent in humidity loss? Our 1930 house has been too leaky to avoid humidity loss, but with our recent gut of several walls we may be on track to achieving this humidity benefit.
I don't think it's quite the same in that the air in contained and recirculated in the dryer. Lint is filtered out of this air loop and water is condensed and pumped out, so the lint never makes it out. Having a heat pump dryer has taught me that lint does get trapped in the successively finer filters of the dryer. In the last filter it's very very fine, more like dust. That's to say that I'd be concerned to vent this air into my house even with some filtration. I appreciate alternative thinking but it's a air quality/health issue.
When it is cool outside the indoor surface temp of your windows is fixed by the quality of window you selected their by setting your max humidity. When you introduce all that moisture it is going to all turn to water on the windows making a mess you will need to clean up.
If you did manage to get the humidity over 55% in the winter, I would be concerned about moisture finding something cold to condense on rot and mold could become a problem hidden in the walls.
Walta
So I am doing an experiment with this. Outdoor temp was 5 degrees F which is by far the coldest day of the year.
I found that the RH was 35% when I started the dryer. An hour after the dryer finished it was still 35%. During the dryer run the windows were still clear, as this wasn't a high temperature load. The walls began to sweat but they didn't drip as a lot of the moisture was venting harmlessly into the larger area of the house which is the point. This is not a problem as we haven't finished the insulation, we have the walls at R20 with spray foam inside and when we finish with another external layer, they will be at R30. Now there would be a problem if the moisture got into the middle of the wall where it could condense inside of the wall. Our contractor is going to be continuing work in this room on Monday which will include sealing up all drywall and putting on a coat of semi gloss paint with the additive that resists mildew.
The plan in this room is to replace the existing window with a triple pane window so that will further reduce the potential for condensation.
Just because we can vent indoors doesn''t mean I will choose to do it for 6 months of the year. I might end up doing it for only 2 or 3 months, when the humidity is at a serious deficit.
If you want to cut down on power usage and also increase interior humidity in the winter, you cannot beat indoor laundry lines.
We just set these up this winter after having makeshift ones we used sporadically the previous winter, and before that we used our heat pump dryer for three years.
The increase in indoor humidity is pretty modest, maybe a few %RH at most. So even if you don't want to increase humidity, it shouldn't be a deterrent.
Other benefits include less wear on clothes, and the ability to put away the clothes whenever it suits you. I always hated taking clothes out of the dryer, because you have to do it within a very short time of when the cycle completes, or your clothes get perma-wrinkled.
Agreed. we already have some racks for indoor drying but as of now we don't have enough drying space for the whole load. We will put one of the racks that was in the laundry room in the kitchen now, because the kitchen will be drier when the dryer is in use!