You've cleaned that window twice this week. From the kitchen it still looks like you never touched it. There's a milky film across the bottom of the glass, worse in the afternoon, and no amount of Windex is doing anything about it.
You're cleaning the wrong surface. The dirty one is sealed shut.
What That Fog Actually Is
A double-pane window is two sheets of glass held apart by a spacer around the edge, with dry air or argon sealed into the gap between them. That sealed gap is the entire point of the window. It's what keeps the July heat on the other side of the wall and your electric bill from going sideways.
The seal around the edge of that gap is the part that fails. Once it goes, humid outside air works its way into the space between the panes and it has no way back out. The water vapor rides in with it and stays.
So what you're looking at is condensation on the inside faces of the glass, inside a sealed pocket about half an inch wide. You can wash both sides of that window until your arm gives out and nothing about it will change. In the trade it gets called a failed insulated glass unit, or just a blown window.
Why It Shows Up Worst in July
The seal probably failed months ago. Summer is when it starts announcing itself.
Every day the sun hits that window the trapped air heats up and expands. Overnight it cools and pulls back in. That's a little bellows breathing humid North Texas air in and out through the broken seal, and July hands it the biggest temperature swing of the year with plenty of moisture to carry.
There's also the daily pattern you've probably already noticed. Morning sun warms the gap, the moisture evaporates, and the glass looks nearly clear. By late afternoon or the next cool morning it condenses again and the fog is back. If the window seems to change through the day, you're not imagining that, and it's one of the better signs of what you're dealing with.
Hail season feeds into this too. A hard DFW storm doesn't have to crack anything to hurt a window. It flexes the frame and stresses the seal, and the failure turns up a season or two later when nobody's connecting it to the storm anymore. If your street took a beating this spring it's worth keeping in mind, and it's the same reason we tell people to walk the house after a big one even when nothing looks broken from the driveway.
How to Be Sure It's the Seal
Two minutes of checking settles it.
Wipe the inside of the glass. Then go outside and wipe the same spot. If the haze doesn't move from either side, it's between the panes and the seal is gone. That's the whole test and it's almost always conclusive.
Look for the other tells while you're out there. A failed unit often shows faint mineral streaks or dried water tracks down in the bottom corner, left behind by moisture that's been cycling in and out for a while. Sometimes there's a visible drip line. On a bad one the two panes look slightly drawn toward each other in the middle, because the gas that used to hold them apart has escaped.
One thing to rule out. If it's a cold morning and the condensation is on the room-side surface, that's just indoor humidity meeting cold glass, and it wipes right off. Different problem, much cheaper one.
Glass Only, or the Whole Window?
This is where people brace for a terrible number, and most of the time they don't need to.
If the frame is solid, the window opens and locks the way it should, and there's no rot, the insulated glass unit can usually be swapped on its own. A glazier pulls the failed unit and sets a new one into the existing frame and sash. It costs a fraction of a full window and it's done in an afternoon. Whenever we look at window work in an Allen home that's the first thing we check, because it's the cheapest honest answer available and a lot of homeowners never hear it.
Replacing the whole window makes more sense when the frame itself is the problem. Rot in a wood frame, a sash that won't stay up, hardware that's given out, or a window that was single-pane and struggling before any of this started. It's also the better call when several have failed at once and you were already thinking about what those windows are doing to your energy bill.
Check your warranty before you spend anything. Insulated glass units usually carry a seal warranty, often ten to twenty years, and plenty of them follow the house instead of the original buyer. A lot of Allen subdivisions built through the 2000s and 2010s sit right inside that window. The manufacturer stamp is in the corner of the glass or down in the frame channel, and finding it costs you one phone call.
Which Ones Go First Around Here
It's rarely random.
West and south-facing windows fail first. They take the worst of the afternoon sun and the biggest daily swing, so the seal works harder than anything on the shaded side of the house. If you've got one foggy window, check the rest of that same wall before you look anywhere else.
Big fixed picture windows are next in line. More glass means more expansion pushing on the seal, and they don't get the small flex relief that a window you actually open does.
Anything over a kitchen sink or in a bathroom or laundry room is living in more moisture than the rest of the house, and that pushes on the seal from your side too.
The pattern is the same one that goes after everything else on a west wall in an Allen summer. That afternoon exposure is what makes vinyl plank flooring buckle by the glass and bleaches whatever furniture sits in that spot. Homes in Twin Creeks, Montgomery Ridge, and Suncreek all went up with big west-facing windows, and that wall is simply doing harder duty than the other three.
What It Costs You to Leave It
Honest answer: a foggy window is not an emergency. Nobody has to fix one this week.
What you're losing is the insulation. Once the gas is out and the seal is open, that window performs closer to single-pane, so the room runs hotter in August and colder in January and your system works harder covering for it. One window and you'll never find it on the bill. Six of them and you will.
The part people actually mind more is that it looks bad and there's nothing you can do about it. It shows in listing photos. A buyer's inspector writes down every failed unit in the house, and that list turns into a line item at closing.
So it can wait until you're ready. Just don't let it sit for five years and quietly become twelve windows.
What to Do This Week
Walk the outside of the house and count. Stand back a few feet from each window in good light and note which ones are hazy. That list is the whole conversation, and it's usually shorter than people expect.
Then find the manufacturer's mark on one of the bad ones and check the warranty before you pay anybody a dime.
If you'd rather have somebody else sort out which ones need glass and which need replacing, give us a call at (469) 242-3276. We've been remodeling homes in Allen since 2010. We'll tell you straight whether it's a glass swap or a full replacement, and if the answer is that three of your windows are fine and one needs a new unit, that's exactly what you'll hear from us.