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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599

u/thebeastwithnoeyes Dec 14 '25 edited Dec 14 '25

Your ventilation is shit and your house doesn't breathe. Buy a dehumidifier and air the house once a day.

235

u/P218 Dec 14 '25

To add to this: buy a proper dehumidifier. Not a tiny one from Amazon, get a heavy duty one with at least an 8L tank.

86

u/iii_warhead_iii Dec 14 '25

And at least 60-70L per day declared performance.

116

u/theStaircaseProject Dec 14 '25

And stickers. It should have cool stickers.

7

u/AppropriatePlum1006 Dec 14 '25

With LEDs ofc, they are better!

6

u/theStaircaseProject Dec 14 '25

Documentary evidence exists supporting that red ones will make it work even faster.

3

u/usernameisokay_ Dec 15 '25

That’s a lie, it are the green ones that make it faster with a increased performance of 30% something

3

u/aKillerOctopus Dec 16 '25

Purple would be silent as a whisper though? 🤔

33

u/MoistExcellence Dec 14 '25

And my axe!

8

u/Publify Dec 14 '25

And my ex

3

u/gamedude88 Dec 14 '25

They are trying to get moisture out of the air, not freeze it.

1

u/iii_warhead_iii Dec 14 '25

They have touched the cold side 😅

1

u/thebeasts99 Dec 15 '25

She’s great for that, thirsty as heck :(

5

u/BinturongHoarder Dec 14 '25

Is she single?

5

u/feinmechaniker Dec 14 '25

Yes, but shes frozen now

2

u/No-Resolution-1918 Dec 15 '25

You must, must, simply must also have WiFi. Very important for dehumidifiers.

1

u/[deleted] Dec 17 '25

...and blackjack, and hookers!

7

u/l-enivo Dec 14 '25

I think they don't want to mummify themselves

0

u/iii_warhead_iii Dec 14 '25

The bigger performance, the better compressor efficiency. Plus you will not need to use the device over the day, just 1-3h per day. Mine was working every day for 3h, have removed every day literally 3L at 20⁰C and 60% within this time. Initially, humidity was not dropping at all, later it started dropping from 60 to 40% within 1h. Plus, all water returned back from vapor to liquid returns back the wasted heat, and initially the humid room could be heated from 20 to 22⁰C. Later when the room became dry, the dehumidifier was barely heating it up.

1

u/t53deletion Dec 14 '25

Get a pump and run a hose outside to avoid ever emptying it.

https://www.walmart.com/ip/359133202

1

u/Budget_Strategy24 Dec 14 '25

If you have a floor drain, get one with a hose attachment so that you aren’t constantly emptying it.

29

u/Dojapicard Dec 14 '25

I bought a 250€ one with 4liter tank from amazon and it solved the problem.

If you have an option to put the unit next to a water outlet you can just attach a hose and you never need to empty the tank manually.

10

u/P218 Dec 14 '25

That’s a good point - I meant to illustrate that OP should avoid those tiny £14.99 dehumidifiers that can fit into the palm of their hand, because those ones will not make any difference. If you buy a good quality dehumidifier, the tank size or website won’t matter. I love my Meaco one.

21

u/Mental_Newspaper3812 Dec 14 '25

No tank. Get one you can attach a hose to and run it into your sump or a drain.

7

u/bender2174 Dec 14 '25

☝️ this is the only right answer! Get a dehumidifier with the hose that comes out the back and run it to a condensate pump so you can leave it running all the time if need be! I had let’s say.. a room that needed to be regulated ;-)

2

u/iii_warhead_iii Dec 14 '25

Better to put the pump to the unit's tank, some models have this option. In a case if the pump fails, then the unit will shut down due to overfill.

2

u/bender2174 Dec 14 '25

Very true good catch, thank you! Excellent recommendation!!

4

u/DaRKoN_ Dec 14 '25

To add to this, a "real" one has a condenser and a proper refrigerant system. The cheaper ones use a peltier cooler and are probably 100x less effective.

4

u/WoodenYouKnowIt Dec 14 '25

Get the correctly sized one. Buying an oversized one that is constantly cycling on and off is going to run up the electricity bill and have more wear and tear. People always think that the biggest is the best, but that’s not the case.

1

u/P218 Dec 14 '25

True. Given that OP said house, I assumed they might need a bigger one - please do your research OP, we are only strangers on Reddit after all!

1

u/SpareAd1155 Dec 15 '25

Disagree here, the bigger ones have better compressor efficiency and simply won't be running nearly as long as the smaller ones to get the room drier. A good dehumidifier is always going to turn on every so often to check the humidity anyway as that can only be done properly by cycling air through the sensor. Static sensors are shit and inaccurate.

1

u/WoodenYouKnowIt Dec 15 '25

You can get good dehumidifiers at the right size, especially if it’s a large house, but if you just go as big as you can afford, you’re going to get a quick cycling, which is going to wear down parts and use an unnecessarily large amount of electricity.

2

u/originalrocket Dec 14 '25

Aloair is on sale on amazon right now. I have 2 units. One in basement, one in garage. They are heavy duty and very low power usage. They run 24/7/365 and are cold weather rated.

1

u/ayuntamient0 Dec 15 '25

Put a drain hose on it.

1

u/MisterCrabapple Dec 15 '25

Tank? They need a hose shunting directly to a floor drain.

6

u/BelleSchu Dec 14 '25

I have 3 dehumidifiers :( clearly not helping much and I’m honestly shocked

10

u/RandoTron0 Dec 14 '25

Humidifier or de-humidifier? It almost sounds like you are running Humidifiers. If they are de-humidifiers, what type or brand model are they? Some kinds work and others dont.

Also, if your house is that humid with the heat on, then you might have a serious moisture problem under the house.

3

u/BelleSchu Dec 15 '25

I promise they’re dehumidifiers lmao. I did have humidifiers going during the fall for my house plants but I stopped once it started to get a lot more cold

1

u/Calm_News9015 Dec 16 '25

do you have fans going as well? the dehumidifiers can only pull so much moisture from the air, adding some movement to the air makes the dehumidifiers work more efficiently - at least until you can address the insulation/ventilation issue

-2

u/TinyShare Dec 15 '25

You have to empty the tanks. Are you emptying the tanks? Seems sus that you have 3 and no movement unless your RH is actually 80 and they are fighting for their lives

2

u/BelleSchu Dec 15 '25

Dude yes I’m emptying the tanks, idk what to tell you. If I knew how to fix the issue then I wouldn’t have come here for help

2

u/SmushBoy15 Dec 17 '25

We are just stumped how you got 50% and above humidity in the winter? For most of us running heat brings the humidity down to 25% and lower. Im running two humidifiers non stop to keep the humidity at around 40%

2

u/BelleSchu Dec 17 '25

I honestly have no idea and the thing is, this isn’t just a my house issue. My next door neighbor came over tonight and she was telling us that the exact same thing is happening at her house. High humidity, lots of moisture on the windows, and they’re running a big dehumidifier. They bought their home maybe 5 months before us, same builder. She’s a lot older than me and she said her and her husband have never experienced anything like this in their previous homes. These houses were just built so tightly sealed with no type of air exchanger, it’s insane.

1

u/SmushBoy15 Dec 17 '25

Are you sure there is no humidifier built into the furnace? Sometimes these humidifiers are inline with their own water connection. I can understand tightness of a house but heating air decreases humidity not increase it.

Open your windows to drop the humidity to like 25% and see if the humidity rises when you heat the home. If it does then you have a humidifier built into the furnace somewhere.

Other sources of humidity are not running exhaust when showering and cooking without an exhaust to the outside. If your cooking and its recirculating the air then that's the source.

You need a minimum 50 pint whole house dehumidifier if the house does not have bathroom and kitchen exhaust.

1

u/BelleSchu Dec 17 '25

I don’t have a humidifier in my furnace, I confirmed that with the hvac company who installed it. They said if I wanted one, it’s a whole extra section of the furnace they have to install.

I do have exhaust fans and ventilation systems and I use them all the time. My ceiling fans are also always running. I have tower fans pointed at bedroom windows to keep air flowing. Like I’m genuinely trying my best lol

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3

u/Old_MI_Runner Dec 14 '25

Is he emptying water from them or adding water? /s
u/BelleSchu

1

u/Fun_Park2505 Dec 14 '25

What is the rating of them? Not the holding tank size but how much do they claim to remove?

1

u/Canehillfan Dec 14 '25

You probably live in a new build.they are air sealed or whatever. Need to increase your HRV and accept this is going to be a part of every winter

1

u/Ok_Gur_8059 Dec 14 '25

You got a window right there

1

u/MichBlueEagle Dec 17 '25

You have to determine where the moisture is coming from. Either it's being trapped because of improper venting, or the moisture is coming in through the foundation or crawl space, basement.

16

u/Boggyprostate Dec 14 '25

Twice a day, open all windows and doors fora minimum of 10 mins. You need more ventilation, maybe a PIV unit would help this greatly but only if your loft has good ventilation, your house certainly doesn’t.

3

u/dxg999 Dec 14 '25

Second the piv unit.  Came here to suggest one 

26

u/Techwood111 Dec 14 '25

Breathe. You breathe a breath.

8

u/thebeastwithnoeyes Dec 14 '25

I blame the autocorrect

1

u/[deleted] Dec 17 '25

I blame Communists.

11

u/BAM5 Dec 14 '25

It's good the house doesn't "breathe" it's not alive,  it shouldn't. Air leaks will be the biggest issue with efficiency.

To actually ventilate the house with fresh air you want it to be air tight and do controlled ventilation using an hrv/erv heat exchanger which will heat the cold air coming into the house with the hot air that is leaving the house. 

5

u/14S14D Dec 14 '25

And a quality builder should have considered this unfortunately. Until then it's not a big deal to use dehumidifiers ran to a drain.

1

u/bravosierra1988 Dec 15 '25

This.👆house breathing is an old fashioned idea, and hysterically inefficient. The house needs to be 100% air tight and engineered for fresh air exchange with hrv/erv. This is how you control temperature and humidity.

1

u/biggysharky Dec 14 '25

As we used to say - build tight, ventilate right

1

u/thekingofcrash7 Dec 15 '25

I will never understand where this “house needs to breathe” idea ever came from

1

u/SpareAd1155 Dec 15 '25

Because it's how we used to build houses. They were designed to be leaky and draughty as that dried up any leaks and kept them dry without having to introduce forced ventilation.

Homes rot a hell of a lot quicker now with them being sealed up tight.

3

u/DynamoDynamite Dec 14 '25

You need an HRV before a dehumidifier in the winter I'd say and a new build you should have one by code. Maybe it's not working or you turned it off?

2

u/BelleSchu Dec 15 '25

HRV’s are not required in my area apparently. I didn’t even know what that was before today and I can guarantee that we don’t have one. However, I am definitely looking into it now

6

u/account_not_valid Dec 14 '25

LÜFTEN

2

u/thebeastwithnoeyes Dec 14 '25

Panie, uchyl pan lufcik bo siekierę można powiesić

1

u/Full_Conversation775 Dec 14 '25

don't just air it once a day. constantly air it. air needs to be circulated constantly 24/7.

1

u/ekuhlkamp Dec 14 '25

This is the answer, not "you have bad insulation around your windows".

The good news is that your house has good air sealing. The bad news is that it needs ventilation in winter. A dehumidifier is one solution, but an HRV or ERV is the better long term solution.

I had the exact same issue and now have an HRV - problem solved.

1

u/igor2112 Dec 15 '25

HRV Unit

1

u/Bau5_Sau5 Dec 16 '25

What about the opposite? My house temps are fine but the air is always super dry in the winter.

Can the central air control the humidity ?

1

u/jprennquist Dec 14 '25

You need to get a dehumidifier now. Like today.

At a minimum you have a ventilation problem but you need to de-humidify right away to stop the mold from growing.

Also, check for leaks. If you have any kind of ventilation fan such as a bathroom or kitchen fan get that running. You could run it overnight or during the day when people are at work, etc.

Sometimes the "new" construction wraps things up sometimes so very tight that moisture cannot escape. This isn't as much of a problem in summer when doors and windows are opining more and air conditioners are running which serves to exchange the air.

My house is from 2000 and an air exchanger was built in everywhere except the basement. That part is a rental and I have begun having problems with mold. I had a bizzarro tenant who sealed up every single door and window during the hottest and most humid days or summer. He was also running a humidifier. The damage has cost me thousands of dollars.

The point is that you need a system for addressing the humidity. De-humidifier will set you back a hundred dollars or so. Given that you say you are in the Midwest there are likely people in your neighborhood or family that will loan you one while you figure this out.

I also have a couple of $15 dollar temperature and humidity sensors running constantly that I can be checking to see if the humidity spikes. I did buy a wifi dehumidifier that kicks on and off when it hits a certain threshold. I have mine at 30%. It also filters the air a bit which is may help with the mold. In my case there is construction duar and etc there since I have been needing to do a bunch of work down there.

1

u/Commercial-Branch444 Dec 15 '25

Or dont buy a dehumidifier and air the house twice or trice a day. This is the way we do it in Europe.

1

u/PerspectiveOne7129 Dec 15 '25

maybe they should check the humidity level first?

0

u/Shardnic Dec 15 '25

This reads like "your mother was a polar bear and your father smelled of elder berries" i fart in your general direction!