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How much condensation on windows is normal?

Dan Box

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Location: Eastern ON

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posted 9 months ago

Greetings!

Now that the cold weather is back, our windows are covered in condensation every morning. I'm in eastern Ontario (Canada eh). Nighttime temperatures are below 10 C / 50 F. Not really cold yet.
In winter it'll be -25 C or worse and sometimes we get ice on the windows (inside). Is it normal/inevitable to have icy windows?

Not sure if it's too much moisture inside, bad windows, or both. And what can I do about it, short of replacing the windows? Ie cheaply.

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James Freyr

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posted 9 months ago

I suspect it's too much moisture inside. Dehumidify the air in your home and I think that the condensate problem will be greatly reduced if not gone altogether.

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Lucrecia Anderson

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Location: Middle Georgia

posted 9 months ago

Uhhh....pretty sure it is NOT normal to have ice on the inside of your windows.

The humidity level should drop considerably once the cold weather sets in. You may also want to put window film on the inside of your windows (shrink wrap plastic, it keeps the house much warmer). I use them every year. You tape it to the window frame so there is a dead air pocket between the plastic and the window, it also stops all drafts. Once it is taped on you use a hair dryer to tighten/shrink the plastic and it becomes completely invisible.

In your case thermal curtains may also be a good idea, they could save you a lot in heating cost. I made a thread on that if you are interested: https://permies.com/t/93472

Jeff Sullivan

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Location: New England

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posted 9 months ago

It's not inevitable, but it can be difficult to completely eliminate, depending on your house and habits. A few things to look in to:

* where is the moisture coming from? Vent fans in bathrooms and kitchens can help a lot with this
* If the windows are old (i.e. single-pane), you should have storm windows. This will keep the interior surface warmer
* If the windows are double-pane, check that the seals are still good (is there moisture or rust inside the window itself?). You can often replace the sash (the part that goes up and down) without replacing the whole window. The good ones have 10- or 15-year warranties.
* An air-tight barrier on the inside of the window (plastic wrap if that doesn't bother you, well-fitted curtains for a longer-lasting approach) will often help, but make sure that you aren't just making a nice spot for mold to grow

Mike Jay

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posted 9 months ago

Hi Dan, I fought this for the past three winters in my new house and finally fixed it. Here's the thread where I reported all my findings Preventing Window Condensation in the Winter

I was going to type up a summary but it's just better to read the thread. Good luck!!!

Lucrecia Anderson wrote:Uhhh....pretty sure it is NOT normal to have ice on the inside of your windows.

Sorry Lucrecia but it is relatively common when the outside temps get down to -10F or so. Assuming your house is at 65 degrees and it's -20 outside, the window panes are somewhere in between. Odds are the interior pane is below freezing. That means that unless the house is below 30% humidity, it's condensing and then freezing. Two winters ago we dehumidified our house for weeks and got the humidity down to 25% and we still had tons of condensation and freezing. With a 1960's house and new double pane windows.

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Lucrecia Anderson

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Location: Middle Georgia

posted 9 months ago

Mike Jay wrote:
Sorry Lucrecia but it is relatively common when the outside temps get down to -10F or so. Assuming your house is at 65 degrees and it's -20 outside, the window panes are somewhere in between. Odds are the interior pane is below freezing. That means that unless the house is below 30% humidity, it's condensing and then freezing. Two winters ago we dehumidified our house for weeks and got the humidity down to 25% and we still had tons of condensation and freezing. With a 1960's house and new double pane windows.

I will admit I hate the cold and have never lived anyplace where the temps drop to that extent. I guess a little freezes and then more condensation keeps attaching itself?

Wouldn't window film help a lot with that? If the condensation is coming from the inside of the house the film stays quite a bit warmer than the freezing cold glass (though not sure how much warmer if it is -20 outside). I use the film and then a heavy multi-layer curtain right over top of it (touching it) and it seems to stop or at least absorb condensation during the winter.

Mike Jay

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posted 9 months ago

You got it. Once that pane of glass is below the dew point, water starts condensing on it. If it's below freezing, the condensation freezes as well. That's actually nicer so the water doesn't run down and rot out the window sill as fast.

The window film helps a bunch by keeping the humidity of the room from continuing to condense against the cold glass. The film itself stays above the dew point if it's at least a few inches away from the glass (as it is in my case). The issue is that any humidity between the film and the window (minor though it is) still condenses and then sits on the window sill all winter mocking you and rotting out the window sill.

Michael Cox

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posted 9 months ago

Condensation can be a real problem, and can do considerable damage to a property. I had tenants move into my house for a few years, while I moved out for work. When I got the property back there was condensation damage in every room - damp patches on walls, rotten window sills, crumbling plaster. This was a house where I had previously lived and never had a hint of an issue.

Turns out they had been running the heating at about 30 degrees C, year round, and drying all their clothes indoors without ever opening windows. The humidity was unbearable, and the moisture had soaked into the structure of the place. It took weeks to dry with a dehumidifiers before we redecorated.

The high humidity was entirely due to how they were using the house - they had shut the ventilation right down, ran the heat high (warm air holds more moisture) and dried everything indoors. Lesson learned for me, as a landlord. I installed fixed air vents in every window frame, after that.

My point is if you are concerned about condensation and humidity you should look and see what changes you can make you how you are using the space - dry your clothes outside, make sure there is adequate ventilation etc... If you really can't dry clothes outside, then consider investing in a condensing clothes drier, so that the moisture does not go into the air.

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Tereza Okava

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posted 9 months ago

I've lived in two places now where double paned windows are unheard of and temps dip drastically (Japan and southern Brazil). Here in Brazil the condensation doesn't freeze, like it did in Japan, but it sure is present.
two things that help (because it needs to be addressed, or else mold....): circulation (if condensation is worst at night, which is my case)-- sleep with bedroom doors open, and electric dehumidifiers (thank god I have mine from Asia). Also, if you cook anything involving humidity (steaming, boiling, etc) try to close off the rest of the house. It's an ongoing battle.

I found when I lived in snow belt places that plastic film helped with drafts but not with condensation (again, single pane windows, no central heating).

Dan Box

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Location: Eastern ON

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posted 9 months ago

Thanks Mike, that thread helps. Seems like you're in a very similar siuation to me. I'll have to look at the plastic film again - we have pretty big windows so it could be an ugly solution.

Are dehumidifiers expensive to run?? I had a glance but didn't see any kwh ratings online. Any other options to remove humidity that don't include another fan whirring endlessly? Of course we could vent more warm, moist air outside but that seems self-defeating when you're trying to keep warm.

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Mike Jay

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posted 9 months ago

I ran a dehumidifier for many days and I'm not sure the usage but I'm sure it bumped up the bill. Once the house was "dry" and we were still condensing, I just kept running the dehumidifier and it seemed to not make a difference.

I thought the film would be ugly but it wasn't as bad as I thought. We have one big picture window (7' by 5') and even that was ok. I used two baggies of desiccant on that one.

The other way is to run your bath fans to exhaust warm humid house air and replace it with cold dry air from outside that you'll then have to heat up. At least it uses infrastructure you already have but it is a fan whirring away and may not get you dry enough either.

On dry fall days you can open the windows and exhaust air. It will cool the house down but it gets it done in less time. Probably not dry enough but it helps and is cheap.

Phil Stevens

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posted 9 months ago

Dan, a decent residential dehumidifier will typically use 200-500W when it's running. If you don't want the electric option, you could get bags of dessicant (silica gel, calcium chloride, etc.) and put those around the house. The dessicant can be refreshed on a stove or in an oven and used over indefinitely...but don't "dry" it inside the house! Biochar or any decent activated carbon is also a good at absorbing moisture, and can also be reused.

One of the best things you could do for the long term would be to figure out a way to bring fresh air into the house across a heat exchanger. This is the essence of Passivhaus ventilation and a good way to have healthy, dry buildings in general.

L Goodwyn

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posted 9 months ago

This is the danger of upgrading an older house. Do not create a closed loop system it will not work. Your heating
systems needs make-up air to function. I.E. your clothes dryer, your furnace, your fireplace, your refrigerator.

What your refrigerator? yes its not a closed loop system. It condenses moisture from the inside and displaces (evaporates) it
to the room. Condensers are on the inside and Evaporators are on the outside of air conditioning systems .
Your refrigerator removes heat (making the interior colder). Everything with mass generates heat.

Dehumidifiers make the air colder to remove moisture(condensing).

The vacuum of space contains heat because its not devoid of mass, (virtual particles that pop in and out of
existence)(CASIMIR effect) the vacuum of space is not and can not be absolute zero due to this.

Back to make up air, if you upgrade windows and heating systems make sure you have adequate make up air
to not create a closed loop system.

New eco buildings are making people sick because they do not have make up air systems. The toxins stay in
the new construction because they are closed systems.

This will eliminate your condensation problems.

Mike Jay

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posted 9 months ago

L Goodwyn wrote:This is the danger of upgrading an older house.

Back to make up air, if you upgrade windows and heating systems make sure you have adequate make up air
to not create a closed loop system.

This will eliminate your condensation problems.

Just to check my system out... I have a wood stove for 95% of my heat, forced air for vacations. Dryer operates once a week and blows outside. Outside air enters via a 4" duct to a cold air trap for make up air for the stove and other consumers. I improved the air sealing and insulation on my 1960s house two years ago. But I had the condensation issues in the winter prior.

I have a hunch if I left a window open all winter in the basement I'd still have condensation issues upstairs.

So what am I doing wrong L?

Lucrecia Anderson

Posts: 538

Location: Middle Georgia

posted 9 months ago

Dan Box wrote: I'll have to look at the plastic film again - we have pretty big windows so it could be an ugly solution.

If it is properly applied it is invisible. Really. Maybe the window kit plastic has been improved over the last few years? I just started using it 3-4 years ago and I don't understand why people say it looks bad. Just think carefully about where you place the tape so it is less noticeable but at the same time secure enough that it won't pull away once you heat shrink it. And be careful when removing the tape as it can strip the paint off some window sills.

Dan Box

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Location: Eastern ON

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posted 9 months ago

One of the best things you could do for the long term would be to figure out a way to bring fresh air into the house across a heat exchanger. This is the essence of Passivhaus ventilation

Thanks Phil.. Any links for that? Sounds like the right idea. I know a bit about heat exchangers/heat recovery ventilators but again, just more expensive boxes with fans.

L is probably right that we're lacking in make-up air. The house was built in the early 80's, not too old or leaky, so not much fresh air coming in. But all the fresh air in the world won't make it dry inside with a family of six.

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S Bengi

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posted 9 months ago

Possible sources of the extra humidity that could be reduced:

Cooking
I have only had that problem went I purposely tried to replicate it by boiling a pot of water (2gallon) until it all evaporated.
It is possible that you do alot of your cooking at home and you leave the lid off or the lids just aren't made the way how others are.

Humidifier
Or maybe you use a humidifier in the winter, lol I know funny, I feel like a tech guy saying is your device pluged in? If you do have a humidifier get a wicker/evaporation type vs the hot steam one or the ultrasonic misting one.

Showers
Turn on the vent if you have one or you could also open the bathroom window after your shower and then close it after 3 minutes
You might want to change over to a laminar-flow showerhead because it won't create as much steam and moisture as a regular aerating one.

Clothes Dryer
The dryer vent might be sending moisture into the house vs outside via leaks or just complete lack of venting

Ways to reduce the window temp: Triple or double pane windows, add some suran wrap or bubble wrap for a "bootleg" double/triple pane.

How to removing the moisture in the air: HVAC/Ventilation system with heat recovery, Dehumidifier, opening windows.

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posted 9 months ago

Might want to see if your windows need a refill of Argon.

Phil Stevens

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posted 9 months ago

Dan - Here is a link to a DIY build:

https://makezine.com/projects/heat-exchanger/

Family of six will definitely pump a lot of H2O into the air.

Dan Box

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Location: Eastern ON

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posted 8 months ago

Timmy Eco wrote:Might want to see if your windows need a refill of Argon.

Anybody know how I might check that?? And is it worth the expense?

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Mike Jay

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posted 8 months ago

I think if they leak out the argon, then they've let normal air in. That leads to condensation between the glass panes. So unless the condensation is between the panes, I think your argon is still doing its job.

Rebecca Norman

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posted 8 months ago

I agree with all that S Bengi says above, and in addition, if you're line drying clothing indoors, of course that adds moisture.

Combustion of gas produces steam as part of its exhaust, so if you use a gas stove without running an exhaust fan, that can add a lot of moisture to the air (as well as, if it's making noticeable moisture you may even be increasing the carbon monoxide in your house!) If adding a ventilator fan seems too difficult, replace some of the cooking with electric versions like an electric kettle, microwave, or the electric pressure cooker below.

A pressure cooker does some great things: it keeps most of the cooking moisture from boiling out into the house, it cooks things much faster, and it uses much less energy to cook the same thing. Pressure cookers are commonly used all over India so I'm used to it, but maybe it sounds too exotic for Canada, I don't know. The Instant Pot is a big hit in the US the past couple of years, an electric pressure cooker with lots of timer settings that make things easy. It can do things like soak your beans and then pressure cook them after the soaking time is finished, or slow-cook stews. It releases less steam into the house than doing the same on the stovetop in a normal pot.

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How much condensation on windows is normal?

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