Condensation Between the Window Panes

You wipe the inside. It does not clear. You wipe the outside. Same fog, same droplets, trapped in the glass. That is condensation between the panes, and it is a different problem from a sweaty sill. A double pane is a sealed unit. When the seal fails, moist air gets in the gap and shows up as fog you cannot reach. No amount of morning wiping, and no honest dehumidifier, will dry the inside of the glass sandwich.

You can live with the fog for a while. It is ugly, it can reduce clarity, and it can stain. It is not, by itself, the same as water pouring into the wall. Do not let a salesperson fold it into a whole-house moisture crisis without looking at the rest of the windows. One failed unit is a glass repair. Every window pouring on the room side is humidity. You might have both. Sort them.

Look at the room-side sill on a cold morning. Dry sill, fog only in the gap: seal failure. Wet sill you can wipe, clear gap: indoor condensation. Wet sill and a fogged gap: both, and the sill still needs the humidity habits while you plan the glass. Rain coming through the frame is a third thing, a leak, and it shows up in storms more than on clear cold mornings.

Replacement is the real fix for a failed seal. Sometimes the sash, sometimes the insulated unit, depending on the window. Get someone who repairs windows to say which. Cleaning, drilling, and "defogging" tricks are a mixed bag and can ruin a unit that was only ugly. Be wary of a cheap drill-and-vent promise that leaves you with a permanent hole. Ask what happens when it fails.

While you wait, do not caulk the weep holes shut trying to solve fog in the gap. Those holes are often how the frame drains. And do not ignore a separate humidity problem because one window is a seal failure. The other panes can still sweat if the house is wet.

If the wood around a fogged window is soft, that may be an old leak or years of room-side condensation, not the gap itself. Soft wood is a carpenter. The glass unit will not stiffen a rotten sill.

Write how many windows are fogged in the gap versus how many have wipeable water. That count keeps the quote honest. A whole-house window package is a big spend. A couple of failed units is a smaller one. You want the quote that matches the count.

Circle the house once with two marks in a notebook. G for fog in the gap, W for water you can wipe. Do it on a cold morning. The list is what you hand a window person. Without it, every pane looks like a reason to replace the wall of glass.

A failed seal can sit for a season while you budget. Water on the wood should not. Wipe the W windows and deal with house moisture even if the G windows are waiting on a quote. The two lists do not have to be fixed on the same Saturday.

If a contractor blames all of it on humidity, show them a G window with a dry sill. If they blame all of it on bad windows, show them a W window that is clear in the gap and wet on the room side. You are allowed to have two problems and to pay for the right one.

Stuffy mornings that worry you belong with a doctor. Anything that means cutting drywall or working on gas equipment belongs with a licensed pro.

Failed seals versus sweaty glass is a plain distinction in When Your House Doesn't Feel Right. $2.99 at https://clearnestair.com/book.