If you’re seeing moisture between the panes, I wouldn’t just chalk it up to humidity. Learned that lesson the hard way.
Yeah, same here—thought it was just a cold snap making things weird, but once that fog wouldn’t clear up for weeks, I knew something was up. My kitchen window had the same crumbly trim you mentioned, and when I pulled it back, there was actually a little mold. I tried the hairdryer trick and everything... didn’t help at all. In my experience, if the fog’s not going away after the weather changes, it’s usually a seal issue, not just condensation.
I hear you on the stubborn fog, but I’ll throw in a slightly different take—sometimes, especially in older homes, you get weird microclimates near certain windows that make things look worse than they are. Our upstairs bathroom window gets all foggy for days in the winter, but it’s actually just from showers and poor ventilation—not a busted seal. The fog always clears up once the weather shifts or we crack the window a bit. Not saying seal failure doesn’t happen (we had to replace two living room windows because of that exact issue), but I’ve seen folks jump straight to “window’s shot” when it’s really just a ventilation or humidity problem.
About that crumbly trim and mold though... yeah, that’s never a good sign. We had something similar in the sunroom, and it turned out to be a slow leak from outside, not even the window itself. Ended up patching some siding and adding flashing instead of replacing the whole window. Kind of wish I’d looked for leaks first before assuming the glass was toast.
The hairdryer trick never worked for me either, by the way—just made the glass warm and foggy in new ways. Sometimes these fixes feel like old wives’ tales more than anything else.
Point is, if the fog sticks around after you’ve tried airing out the room and checking for obvious leaks or drafts, then yeah, probably a seal issue. But I wouldn’t rule out other stuff right away—especially if your house is older or you’ve got odd airflow in certain rooms. Sometimes it’s just about figuring out where the moisture’s really coming from before shelling out for new windows.
I get where you’re coming from about microclimates and humidity, but I think it’s easy to underestimate how much energy you can lose through even a little window fogging. Here’s my take: if you’re seeing condensation between the panes (not just on the inside or outside surface), that almost always means the seal’s shot, and your insulation is compromised. Even if it clears up sometimes, that air gap isn’t doing its job anymore. Before replacing, I’d try this—check for drafts around the frame with a candle or incense stick, then use a moisture meter on nearby trim. If both are fine, maybe it’s not urgent... but I’d still keep an eye on your heating bills. Sometimes the leak shows up there first.
I get the concern about energy loss, but I’m not totally convinced that every bit of fogging between panes means you need to jump to replacement right away. Like you said,
That’s true, but in my place (built in the late 90s), I had a couple windows with mild fogging for over a year. Heating bills didn’t really budge, and the draft test didn’t show much either.“if you’re seeing condensation between the panes (not just on the inside or outside surface), that almost always means the seal’s shot, and your insulation is compromised.”
Here’s what worked for me:
1. Waited through a full winter before deciding.
2. Used a space heater in that room to see if it made any difference—didn’t notice much change.
3. Kept an eye out for any moisture damage on the sills or trim—nothing showed up.
If it gets worse or you see water pooling, then yeah, probably time to think about replacing. But in my case, it was more of an eyesore than an actual problem. Just depends how much the look bothers you, honestly.
That lines up with what I see a lot—minor fogging doesn’t always mean you’re hemorrhaging energy. If the condensation is just a little haze and not puddling or dripping, you can usually hold off. I’d add that sometimes the argon or krypton gas between panes leaks out, which lowers insulation a bit, but not always enough to notice on bills right away. If you’re in a milder climate or the window isn’t in a critical spot, it’s often more about the look than performance. Still, if you start seeing wood rot or mold around the frame, that’s when I’d move replacement higher up the list.
If the condensation is just a little haze and not puddling or dripping, you can usually hold off.
I get that, but I’m not sure I’d always wait. In my place, that “little haze” turned into a bigger mess after a few months—ended up with a musty smell and had to deal with some hidden mold. Maybe it depends on how old the windows are? I’d probably keep an eye on it, especially if the frame’s wood.
Maybe it depends on how old the windows are? I’d probably keep an eye on it, especially if the frame’s wood.
That’s a fair call. In my experience, once you spot haze inside double panes, especially on older wood frames, it’s rarely just “weather.” I’ve seen folks ignore it and end up with rotten sills or warped trim—sometimes it creeps up on you. Have you noticed if the condensation is worse after showers or cooking? Sometimes the culprit’s just poor ventilation rather than a window issue... but wood frames really don’t forgive much moisture.
I had this exact debate with myself last winter. My house is a 70s ranch with the original wood windows—so, not exactly airtight anymore. I used to see fog on the glass after a shower or when boiling pasta, but that would clear up after a bit. What got me worried was when the haze stuck around between the panes, no matter what I did. That’s when I realized it wasn’t just humidity from cooking or showers.
One of the bedroom windows started showing that cloudy look in the middle of summer, which seemed off since we weren’t running humidifiers or anything. Turns out, the seal had failed and moisture was trapped inside. The wood frame around it started to feel a little soft at the bottom—nothing dramatic, but enough to make me nervous. I ended up biting the bullet and replacing that window before it turned into a bigger project. Not cheap, but better than dealing with rotten wood later.
On the flip side, I’ve got a bathroom window that fogs up like crazy when someone takes a hot shower, but it always clears up within an hour. That one’s just poor ventilation—cracking the window or running the fan helps a lot. Never had any trouble with rot there.
I guess my rule of thumb now is: if it’s condensation on the inside surface of the glass and goes away, it’s probably just humidity in the house. If it’s between panes and sticks around, especially with old wood frames, that’s usually a red flag for me. And yeah, wood doesn’t give you much leeway... once it starts soaking up water, you’re on borrowed time.
Funny how you start noticing these things more as your house gets older—or maybe as you do!
if it’s condensation on the inside surface of the glass and goes away, it’s probably just humidity in the house. If it’s between panes and sticks around, especially with old wood frames, that’s usually a red flag for me.
Couldn’t agree more—once you see that haze between panes, it’s game over for the seal. I’ve tried the “wait and see” approach before, hoping maybe it was just a weird weather thing. Nope. Ended up with a soft window sill and a musty smell that took weeks to clear out. With wood windows, you really can’t mess around. Quick fixes like running a dehumidifier only buy you a little time if the seal’s shot. I’d say if you’re seeing persistent fog between panes, don’t wait—your future self will thank you when you’re not replacing half the frame.
I get the concern about fog between panes, but I’ll play devil’s advocate for a sec. I had a double-pane window in my old place that would fog up between the glass every winter morning, then clear up by noon. Never actually got worse, and the frame stayed solid for years. Maybe I just got lucky, but sometimes it’s not an instant death sentence for the window. That said, if you get that musty smell or soft wood, yeah, that’s a different beast. Just saying—sometimes it’s worth watching for a bit before you rip the whole thing out.