If your window is foggy, cloudy, or has moisture trapped between the panes that you can't wipe away, the insulated glass unit (IGU) seal has failed. It's one of the most common window problems we see in New Jersey — and the good news is that it often doesn't require replacing the whole window. In many cases we can replace just the glass. This guide explains why glass fogs, what NJ's climate does to seals, and your real repair options.
The most important thing to know up front: foggy glass isn't a cleaning problem and it isn't purely cosmetic. The window has lost the sealed gas fill that gives it its insulating value, so it's also quietly costing you energy. Here's the full picture.
What's actually happening — IGU seal failure
A modern energy-efficient window isn't a single piece of glass — it's an insulated glass unit: two (or three) panes separated by a spacer, with an inert gas like argon sealed in the gap and a desiccant in the spacer to absorb any trace moisture. That sealed gas layer is what makes the window insulate.
When the perimeter seal fails, two things happen: the argon gas escapes, and humid outside air works its way into the gap. The desiccant eventually saturates, and moisture starts condensing on the inside surfaces of the panes — the fog you see. Because it's sealed inside the unit, you can't clean it off from either side, and it comes and goes with temperature and humidity.
So foggy glass is a definitive sign: that window has lost its seal and much of its insulating performance, even if it still looks intact otherwise.
Why New Jersey's climate fails window seals
Seal failure is largely a function of thermal cycling, and NJ delivers plenty of it. The daily freeze-thaw swings of a NJ winter, combined with hot humid summers, expand and contract the glass, spacer, and seal constantly. Every cycle stresses the seal a little more until it eventually breaks down.
South- and west-facing windows fail first, because they take the most sun and the biggest daily temperature swings. Age matters too — typical IGU seal life is roughly 10-20 years, shorter for lower-quality original units with cheap spacers and seals. First-generation double-pane windows from the 1980s and 90s are the ones we most often find fogging across a whole house.
Does foggy glass matter if I can still see okay?
Yes, for three reasons. First, energy: the window has lost its gas fill and a good chunk of its insulating value, so it's leaking heat and adding to your bills. Second, it gets worse — the fog deepens over time, and persistent moisture eventually etches the glass permanently, leaving a haze that can't be cleaned even after the unit is replaced. Third, it's a signal: if one or several units have failed, the rest of that generation of windows is aging on the same clock.
It's not an emergency, but it's not nothing. A foggy window is an underperforming window, and the longer it goes the more likely glass-only repair gives way to needing the whole unit.
Your repair options
Replace just the glass unit (IGU). If the frame and sash are sound, we can often replace only the failed insulated glass unit and keep your existing window. This is far less expensive than full window replacement and is the right move for a sound window with a failed seal — common on newer homes where one or two units have fogged.
Full window replacement. When the frame or sash is also failing, when many windows across the home are fogging and aging together, or when the windows are old and inefficient beyond just the seals, replacing the windows makes more sense than chasing individual glass units.
When glass-only isn't possible. Some windows have non-serviceable, factory-sealed sashes where the glass can't be separated from the frame, and some older or oddly-sized units no longer have a matching IGU available. In those cases the sash or window has to be replaced. We'll tell you honestly which situation you're in.
Glass-only vs whole-window — how to decide
The decision comes down to the window's age, how many units have fogged, and the condition of the frames. One or two fogged units on otherwise-good, reasonably new windows point to glass-only replacement — keep the windows, swap the failed units. A whole house of aging, drafty windows with several fogged units points to whole-home replacement, where you're getting efficiency and comfort gains beyond just clearing the fog.
There's a cost crossover, too: replacing a couple of glass units is clearly cheaper than new windows, but replacing glass units one at a time across a dozen failing windows can approach the cost of just replacing them — at which point new windows give you far more for the money. We lay out both numbers so you can decide. Our window cost calculator helps you scope the full-replacement side.
Preventing it — what to look for in new glass
You can't make a seal last forever, but quality buys you years. When you replace glass or windows, look for a unit with a warm-edge spacer (which handles thermal cycling better than old aluminum spacers), a quality dual-seal construction, and argon fill with a Low-E coating for NJ's climate.
Just as important, look at the warranty. A good manufacturer covers the glass seal specifically — often for 10-20 years or even a limited lifetime — which is exactly the failure mode that produces fogging. We spec units with strong seal warranties so a future seal failure is covered rather than out-of-pocket.