First, tell the two apart
Condensation on the inside surface (you can wipe it) — normal. That's humid indoor air meeting cold glass. Common on Utah winter mornings, especially in kitchens and bathrooms.
Condensation on the outside surface (you can wipe it) — also normal, and actually a sign of a well-insulated window. It happens on cool mornings when the outer pane is colder than the dew point.
Fog between the panes (you cannot wipe it, from either side) — seal failure. That's the one this article is about.
What's actually happened
A double-pane window is two pieces of glass with a sealed, dry air or argon gas space between them. That sealed space is the insulation.
When the perimeter seal fails, the gas escapes and humid outside air gets in. That air carries moisture. When the glass gets cold, that trapped moisture condenses — and it can't go anywhere.
Over time it gets worse, and mineral residue from repeated condensation can leave permanent staining on the interior surfaces of the panes.
Why cleaning can't fix it
We get this call a fair amount, and we always tell people the same thing before they book: if the fog is between the panes, we can't clean it out. The surface is inside a sealed unit. There's no access.
We'd rather say that on the phone than take your money and show up.
What actually fixes it
Replace the insulated glass unit (IGU). In most cases the frame is fine and only the glass unit needs replacing. That's substantially cheaper than a full window replacement, and it's what a glass company will typically recommend.
Replace the whole window. Necessary if the frame is also damaged, or sensible if the window is very old and you were planning to upgrade anyway.
"Defogging" services. These exist — a hole is drilled, the unit is cleaned and vented. It can improve appearance, but it usually doesn't restore the insulating value, because the sealed gas space is gone. Some people find it a reasonable stopgap. Go in with clear expectations.
Does it need fixing right away?
It's not an emergency. A failed seal is a performance and appearance problem, not a safety one. The window still keeps weather out — it just insulates like a single pane now, which shows up on your heating bill and as a colder spot in the room.
Most people replace failed units as budget allows, prioritizing the rooms they use most.
Who to call
Not us — this is a glass company's job. We'll happily tell you what we're seeing when we're at your house, but we don't want to sell you a cleaning that won't help.
Have other windows that can be cleaned? Get a free quote.