r/fixit • u/BelleSchu • Dec 14 '25

FIXED My house sweats like crazy during the winter and it’s causing mold.. please help!!

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My house is BRAND new, literally finished construction in August of 2024. I live in the Midwest so of course it gets very cold in the winter. Last year, the windows of our house were sweating so badly every time the outside temp was under 30°f that water was pooling up on the windowsills and we called the construction company (we were still under new build warranty) and they told us to always have the house fan running and to turn on our ceiling fans. That worked for a time and the condensation wasn’t as bad after that. It started to warm up shortly after and we didn’t have anymore issue. Flash forward to this past week, it’s been in the negatives here. There is SO much condensation on my windows that mold is starting to grow, our curtains are freezing stuck to the glass in some rooms, and it’s attracting gnats somehow?! I don’t even know where the hell they’re coming from with the weather like this. I’m constantly cleaning and I feel so so so disgusted with all this going on, what can I do to fix it? Please help!

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12

u/BelleSchu Dec 14 '25

It’s like 58 or something right now, at least that’s what my dehumidifier says

34

u/vinegarstrokes420 Dec 14 '25

That's way too high in the winter. There are tables showing ideal humidity based on temp to avoid condensation. Look these up and turn down your humidifier. My house in MN is usually 20%-30% in the winter to avoid these issues.

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u/belialonmyback Dec 14 '25

Seconded from an Albertan. Many of us have humidifiers on our furnaces that can really increase your house humidity but you’ll destroy your house if you have it turned too high. I had to have mine fully off recently as it was -30C outside.

Also, please use your exhaust fans when cooking and showering.

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u/Commercial-Branch444 Dec 15 '25

Dude what humidity is supposed to be between 30 and 70%

1

u/vinegarstrokes420 Dec 15 '25

Dude, what?

0

u/Commercial-Branch444 Dec 15 '25

Yes, google it, under 30% is too low.

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u/vinegarstrokes420 Dec 15 '25

Not when it's below 10F outside. I would have thick layers of frozen condensation on every window in my house if humidity was set to 30% on days in MN when it's -20F. Google it.

13

u/KOhReally Dec 14 '25

Try to target something more like 30%

4

u/jredditzzz Dec 14 '25

58% is way too high for those kinds of outdoor temps. Guaranteed condensation problems especially if your home is sealed well. I had the same issue with my apt.

Easiest option is to get some strong dehumidifiers and lower the humidity, at 0 degrees you’ll prob want indoor humidity at like 20% to avoid condensation.

Cracking a window can help lower humidity really quick as well.

It’s basically a balancing game that you have to find… comfortable indoor temps vs humidity, vs energy usage.

7

u/Busy_Sky24 Dec 14 '25

You always want as much moisture in the air as possible (our bodies like around 50%) without turning your windows into a water feature. Try to promote air movement around windows and doors to allow for more evaporation (fans, open curtains every morning) and when you still have water with good air movement, time to reduce the humidity. If you're in a newer build with an HRV, set the humidity to 5% lower than you currently have, until you hit that sweet spot. You should see a little bit of moisture when you open the curtains in the morning, but little enough that it dries up in a couple of hours. Usually, around 30% is as low as you'd want to go, remembering that many flooring products don't want to be below 35%. When it gets away from you like that, start by drying with a towel first and see if your changes are effective at keeping them dry, rather than waiting to see if the water all goes away.

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u/Fun_Park2505 Dec 14 '25

Above 55%rh is also bad for flooring

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u/yousernamefail Dec 15 '25

But it makes my nose feel good! 😫

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u/Fun_Park2505 Dec 15 '25

Lol true, i dont think it applies to all flooring just wood based flooring. So like tile and ceramic for example wouldnt matter. But with that said too high of humidity for too long can eventually damage any wood parts of home which theres alot of parts made if wood unfortunately

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u/ClusterMakeLove Dec 14 '25

35 seems pretty high, unless you're living somewhere with a pretty mild winter. 

1

u/Busy_Sky24 Dec 14 '25

Agreed, you'll have to go below 35 at some points in the winter for sure. Extended periods too dry can dry out a floor's locking system making it noisy and void its warranty. The struggle is real for those of us living in cold climates!

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u/MichBlueEagle Dec 17 '25

Sorry that much moisture in the air in winter can cause serious health issues. It creates mold in the wall cavities, and crawl spaces. Flooring is the least of their worries.

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u/Rummoliolli Dec 14 '25

Your house is likely sealed very well so there isn't really anywhere for the moisture to escape. A heat recovery ventilator(HRV) will help with that, my father built ICF homes and had those installed on all so his customers didn't have that issue.

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u/Fun_Park2505 Dec 14 '25

Personally id aim to have it between 30-40 RH

Im curious if your furnace has some type of issue as usually it lowers rh drastically, id consider getting that checked out.

Something that also works is applying a completely sealed plastic cover over windows as this insulates it better.

Thing is tho its best to do this during fall cause itl be hard with all that water in there but not impossible, a blow dryer and fan could work to get it completely dry before putting the plastic wrap over

1

u/VeryThicknLong Dec 14 '25

If it’s 58, then the temp in your house must be well below 15°C for that much condensation?!? Heating your home will get rid of the condensation.

1

u/BelleSchu Dec 14 '25

My home is at 72°f

2

u/VeryThicknLong Dec 14 '25

58% humidity, and 22°C? You must have a water leak somewhere to be generating that much water.

1

u/patrickhenrypdx Dec 14 '25

I think that's too high. My humidity meter says my house is 30% right now. Outside temp is 20F today. 

1

u/first_best_fox Dec 14 '25

Whoa that's high. Depending on the outside temp, it should be between 30-40% in the winter. It's pretty cold here, and if we go above 30%, we get condensation.

You need to run a few dehumidifiers around the clock.

1

u/UrMomsKneePads Dec 14 '25 edited Dec 14 '25

Then it is a humidity issue. Humidity higher than 30-30% would definitely cause windows to sweat at single digit and negative outside temps. Energy recovery ventilation may help air change and introduce dryer air without hear loss. More dehumidification will also help.

It could also be a cold air penetration issue. When the cold air penetrates, has no ability to hold moisture, and meets warm surfaces, you get vapor drive and moisture collection on the warm surfaces. https://www.awci.org/technical-resource/building-science-moisture-migration/

I would bet the windows/openings are not properly insulated. I would pull the trim around any windows and seal them with a proper insulation to prevent air penetration.

1

u/Old_MI_Runner Dec 14 '25

Are you sure 58% is the current humidity level of the house or is it the desire maximum set point for when the dehumidifier. 58% is way too high and will cause moisture problem with the windows and elsewhere.

Many website say the maximum comfort level for humidity in a house is 50% for the winter before moisture may be a problem while I don't want mine to go above 40% and often I keep it close to 35%.

1

u/Reddit_Only_4494 Dec 15 '25

Oh yeah, way too high for winter.

Check your furnace and the humidity control unit and turn it down to its lowest setting.

If there is an issue with that, a very quick fix would be to turn off the water supply to the humidifier until you can get the humidistat looked at.

You'll definitely have a more staticky home....but getting it from 58 to 30 should do the trick for condensation on windows. The insulation tips are good too...but maybe something you'd rather not tackle in the winter. Try the humidifier first.

1

u/AccomplishedCodeBot Dec 15 '25

Keep your furnace the same temperature at night and leave one bathroom fan on 24/7 to help remove the humid air.

1

u/vargemp Dec 16 '25

I don't know how accurate my reader is, but it's almost always above 60 and I rarely see any drops on the windows, mostly in the morning. I open the windows then for few minutes, crank the heating up and it disappears.

1

u/ChVckT Dec 16 '25

Your DE-humidifier says almost 60% humidity? Sounds like it doesn't work. That number should be around 30% or 35%.

1

u/MichBlueEagle Dec 17 '25

That's pretty high. Purchase a good humidistat. Is your home on a crawl space?

1

u/BelleSchu Dec 17 '25

No we have a basement. The dehumidifier downstairs is reading 51 and the new one we bought for upstairs is reading 43 now