Why Is There Condensation on the Inside of My Windows?

LESLIE: Denise in Ohio is on the line with some window condensation. Tell us what’s going on.

DENISE: I’ve got some windows; they’re double-pane. The house is about 10 years old. And I’m constantly battling condensation in the windows. I typically, with a lot of the windows, open them daily and close them at nighttime. If there’s some windows that I don’t get to in the wintertime, when it gets really cold, there is water dripping. It pools, it turns to ice. I try and get some of that putty-type stuff that you can put in the bottom and along the sides.

TOM: Is the condensation inside the panes of the windows or is it like on the inside surface?

DENISE: Inside surface of the house.

TOM: Alright. And these are thermal-pane windows or single-pane windows?

DENISE: Double.

TOM: Well, clearly, the insulated glass is not insulated, so that’s why you’re getting this level of condensation. If you had truly insulated glass, it would be too warm for this condensation to occur. But you have warm, moist air in the house, it’s striking the very, very cold, virtually uninsulated glass and then condensing on that glass and dripping down. So that’s what’s going on; that’s what’s causing the moisture. It’s nothing more than, unfortunately, bad windows.

So, with that said, replacement windows are in your future. Now, you don’t have to do it immediately but it’s a project you’re going to have to face. I mean the good news is that replacement windows, the costs have come down. They’re all custom-made by just by nature, so the company will measure the windows in your house. And by replacing them, they simply pull out the sashes – the old sashes – and slip in a new window into the old hole. And it looks great, it works well. It’s just a good system. So that’s in your future.

For now, though, what we need to do is two things: we need to take as much humidity out of the house as we can and secondly, I’d like to see you get a barrier in front of those windows. So, if you could use, for example, an insulated shade – one that has sort of those honeycomb kind of designs – that would help a little bit.

DENISE: I’ve got double right now and I’ve just ordered triple for some other windows.

TOM: Well, that will help because that, basically, will stop some of that warm, moist air from hitting the window. And also drapes. Shades and drapes help the situation.

In terms of the humidity, there are a number of ways we can attack this. First of all, you want to make sure you start outside your house, look at the drainage conditions at the foundation perimeter. Because believe it or not, if water is allowed to collect around the foundation and it doesn’t run away from your house, if the gutters aren’t extended away from the house, that foundation will absorb water and it will release into the air once it gets inside. That adds to the humidity. So I would definitely do that.

Secondly, I would ask you to check to make sure that all your vent fans are venting out, not recirculating. Because that will help, as well.

And thirdly, up in the attic, you want to make sure that you’re well-ventilated. Because that vapor pressure starts at the basement or first floor – will permeate all the building materials and end up in the attic. And if the attic’s not ventilated enough, it’s going to kind of hang right there.

So, those are ways to reduce humidity inside the house. Of course, you could also use a whole-home dehumidifier. But I think, in this case, if we just control moisture and try to get something that’s protecting those windows, that’s the best you’re going to do short of replacing them.

DENISE: Well, what about getting some circulation? If I open them earlier in the morning and get some circulation going, will that …?

TOM: Nah, you’re – listen, this is just science, OK? Warm, moist air against cold surface equals condensation, you know? You see this in the summer when you go outside with a glass of iced tea and moisture forms on the outside of it. It’s the same thing. It’s just happening in the winter in your house because everything is reversed: the warm, moist air is inside the house and that cold glass is your window.

DENISE: Yes. And unfortunately, we have to keep the humidity at a certain temperature because of asthma and allergies.

TOM: Hmm. Yeah.

DENISE: Alright. Didn’t get as good a window as I thought I did. Alright. Thank you.