When is a foggy window just weather, and when is it a problem?

I get where you’re coming from—those new windows can actually make it seem like there’s more of a problem when it’s just your house holding humidity better. I see this a lot: folks swap out old leaky windows, then suddenly notice fog or condensation that wasn’t there before. The thing is, a little fog on the inside surface (the part you can touch) usually just means the air inside is humid and the glass is cold. That’s not a window issue, more like a ventilation one.

But once you spot that cloudy haze between the panes—where you can’t wipe it off—that’s the red flag. That means the seal’s failed and moisture’s got in where it shouldn’t be. One window feeling colder than the rest could mean a draft, or sometimes just a spot where insulation isn’t as tight.

Running a dehumidifier helps, but if you keep seeing fog trapped inside the glass layers, it’s probably time to look into repair or replacement for that window. Otherwise, it’s mostly just about keeping your home’s humidity in check... not always easy in winter, but worth trying.

Seen this a bunch—folks think the new windows are “broken” when the truth is, their old ones were just so drafty everything dried out faster. Had a customer who called me out mid-January, swearing her new kitchen window was defective. Turned out she’d started drying laundry inside and closed off the vents for “efficiency.” Big surprise: foggy glass. Once she cracked a window and ran her bath fan, problem solved. But if you ever get that stubborn fog between the panes, yeah, that’s a different story... no amount of venting will fix a busted seal.

That’s a fair point about the difference between surface condensation and fog inside the panes. But I do wonder if we’re sometimes too quick to blame “user error” when it comes to moisture on new windows. I mean, yes, closing off vents and drying laundry indoors will definitely spike humidity, but there’s more to it than just habits.

I’ve seen cases where even with regular ventilation—bath fans running, kitchen hood on, windows cracked in mild weather—you still get persistent condensation on brand-new windows. Especially in really tight houses built or retrofitted for energy efficiency. It can be a sign that the home’s overall moisture management isn’t quite dialed in, not just that folks are doing something wrong.

“But if you ever get that stubborn fog between the panes, yeah, that’s a different story... no amount of venting will fix a busted seal.”

Totally agree here. Once you see that milky haze trapped *inside* the glass sandwich, it’s almost always a failed seal—nothing to do with indoor humidity at that point. That said, I’ve noticed some confusion among homeowners about where exactly the condensation is showing up. Surface fog wipes away; inner-pane fog sticks around no matter what you do.

One thing I’m curious about: does anyone else notice more window condensation after adding insulation or air sealing? I upgraded my attic and rim joists last fall (old 1950s house), and suddenly had to start watching my indoor humidity way more closely. Didn’t expect such a difference—almost like the house stopped “breathing” overnight.

Maybe it’s less about blaming people for not venting enough and more about helping folks understand how these upgrades change the whole balance of air and moisture. Drying laundry inside was never an issue before my place got tighter... now I have to run dehumidifiers or crack a window even in winter. Not saying drafty old windows are better—but sometimes, they did make things simpler in their own leaky way.

I mean, yes, closing off vents and drying laundry indoors will definitely spike humidity, but there’s more to it than just habits. I’ve seen cases where even with regular ventilation—bath fan...

That “house stopped ‘breathing’ overnight” line really hits home for me. After I had spray foam put in the crawlspace and attic, condensation started popping up on our brand new windows, even though we weren’t doing anything different. Before that, the place was drafty as heck but never had wet sills. It’s like tightening up the envelope just shifted the problem from cold drafts to trapped moisture—now I’m chasing humidity with a hygrometer and a dehumidifier, especially when it’s cold out. Funny how fixing one thing can create a whole new set of quirks.

- Been there, done that. Tightened up our 70s ranch and suddenly I’m on a first-name basis with my dehumidifier.
- Funny how “energy efficient” can mean “moisture detective” now. Used to be cold toes, now it’s foggy glass.
- You’re not alone—seems like every fix comes with a new quirk. At least we’re saving on heating bills... I think?
- Silver lining: at least you know your windows work. If only houses came with a manual for this stuff.

- Totally get where you're coming from—tightening up an older house is a bit of a trade-off.
- More efficient? Definitely. But yeah, the humidity takes some wrangling now that the drafts are gone.
- I used to think foggy windows meant a bigger issue, but half the time it’s just our wild Midwest weather doing its thing.
- Still, I’d rather run the dehumidifier than pay for heat leaking out all winter... even if I have to empty that bucket more than I’d like.
- If only there were a “house quirks” section in the manual, right?

I’m right there with you on the trade-offs. After I sealed up my 1950s place, I was surprised by how much more I had to pay attention to humidity. The dehumidifier’s basically my new best friend—definitely beats watching my heating bill spike. And yeah, sometimes those foggy windows are just the Midwest being... well, the Midwest. I do check the seals every now and then, just in case, but most of the time it’s nothing serious. Wouldn’t mind a manual for all these quirks either—seems like each house just makes up its own rules.

I totally get that—sometimes I feel like my house is just testing me. For me, the red flag is when the fog is *between* the panes, not just on the inside or outside. That’s usually a busted seal and means trouble. But if it’s just surface condensation, especially after a shower or when it’s freezing out, that’s usually nothing to stress over. Still, I wish someone handed out a “quirk manual” at closing… would’ve saved me a few panicked googling sessions.

I get where you’re coming from, but I’d push back a bit on the idea that surface condensation is “usually nothing to stress over.” Here’s the thing: while it’s true that fog *between* panes is a classic sign of a blown seal (and yeah, that’s a pain), even regular condensation on the inside can be a warning if it’s happening a lot or in weird spots.

You mentioned,

But if it’s just surface condensation, especially after a shower or when it’s freezing out, that’s usually nothing to stress over.

I used to think the same until we moved into our current place—a 1980s split-level with original windows. For the first winter, I shrugged off the beads of water on the living room glass. Fast forward to spring, and I found black mold in the window tracks and even some peeling paint on the sill. Turns out, our humidity was way too high and the windows just weren’t insulating well anymore. Surface condensation was basically my house waving a red flag.

If you’re only seeing it after long showers or on really cold mornings, sure, probably not an emergency. But if it sticks around or shows up in rooms you barely use, I’d say it’s worth checking your indoor humidity (those cheap hygrometers are surprisingly helpful) and maybe looking at ventilation. Sometimes it’s less about the window and more about what’s going on inside the house.

And honestly, I agree about the “quirk manual”—I can’t count how many times I’ve wished for one. But after dealing with moisture issues for a year, I’d rather overreact to condensation than ignore it. Fixing a bit of humidity now is way cheaper than replacing window frames or dealing with mold later. Just my two cents from the “learned the hard way” club...

Totally agree with this—surface condensation isn’t always harmless. I had the same thing happen: ignored it for a winter, then found peeling paint and that nasty black mold in the corners.

Surface condensation was basically my house waving a red flag.