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TroubleshootingWindow Repair

Why is there condensation between my window panes?

Moisture or fog between the two panes of a double-pane window means the seal around the glass unit has failed and humid air is getting into the gap.[^andersen] It cannot be wiped off or stopped from coming back, and the lasting fix is a replacement glass unit or window. Moisture on the room-side glass is a different problem: it comes from indoor humidity.

Free to ask. Local shops send quotes, and you pay only when you book one.

By Kasra Taheri, Founder, LoclisPublished

Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.

Step by step

Read when to stop and call a pro, further down this page, before you start.

  1. Step 1: Find out which surface is wet

    Wipe the fogged glass on the room side, then on the outside. If the fog stays where it was, it is between the panes and the seal has failed.[1]

  2. Step 2: Rule out indoor humidity

    If the wet side is the room side, the cause is indoor humidity, not the window.[1] Check the humidity with a hygrometer; in winter aim for 30 to 35 percent.[1]

  3. Step 3: Look at every window

    Note which windows are fogged and whether the fog comes and goes with the weather. A failed seal usually shows up again after you wipe the glass or the weather turns.

  4. Step 4: Photograph and note the brand

    Take a photo of each fogged window, inside and out, and note the brand if it is printed on the glass spacer or the frame.

  5. Step 5: Check the warranty

    Find the purchase or installation paperwork. Window and installation warranties can run for different periods on different parts of the window.[2]

  6. Step 6: Lower indoor humidity meanwhile

    Run the bath and kitchen fans while you cook and shower, and open blinds in the day so warm air reaches the glass.[1]

  7. Step 7: Get a written quote

    Ask a window pro whether the glass unit alone can be replaced or the whole window should be, and ask for the price in writing.

The short answer

A double-pane window is two sheets of glass with an air space in between.[1] Condensation in between the two panes of glass is a sign that the seal on the window has failed.[1] Humid outside air has found its way into the gap, and it will keep coming back.

Once the seal breaks, the moisture between the panes cannot be prevented from forming, and the ideal solution is to replace the window.[1] In practice a window pro will tell you whether the glass unit alone can be swapped into the existing frame or the whole window should go. Either way it is a repair to plan and price, not an emergency.

A double-hung wooden window with six panes in each sash and dark shutters on a stone facade, in black and white
Photo: GSA, National Parks Service, Public domain, via Wikimedia Commons

First, find out where the moisture is

Not every foggy window has a bad seal. Where the moisture sits tells you what is going on:

  • Between the panes, and it stays when you wipe both faces: the seal has failed.[1]
  • On the room side: the humidity level is too high indoors, not because something is wrong with the window.[1] A strip of condensation only around the edge of the glass can come from a metal component that touches both the outside and inside of the window.[1]
  • On the outside: that is dew, and it is not a sign the window is failing.[1]

Wipe the inside face first, then the outside. If the fog does not move, it is between the panes.

If it is a room-side problem

Lower the humidity. In the winter months, aim for 30 to 35 percent humidity in the home;[1] a cheap hygrometer will tell you where you are. Run the bathroom fan until the mirror is clear and the kitchen fan while cooking.[1] Open blinds and drapes during the day so warm air reaches the glass.

If the seal has failed

The glass still works as a window. What you lose is some insulation, and over time the fog can leave film or spots on the inside faces of the glass that no cleaner will reach.

A few things are worth doing before you call anyone:

  1. Photograph each fogged window and note how many are affected.
  2. Dig out the purchase or installation paperwork. Window and installation warranties can have different time periods for different parts of the window,[2] so a young window may be covered even if the house is older.
  3. Ask the maker or installer whether the glass unit alone is available, and whether a service call is covered.

Treat the quote the way you would any window job. Ask for the price in writing, ask whether it covers the glass unit only or the whole window, and ask who handles trim and caulking afterwards. For what drives that price, see how much window repair costs in Virginia.

Skip the drill-a-hole and spray-clearing fixes. They leave the unit open to the room's humidity and the fog returns.

Older windows with storm windows

An old wood window does not have a sealed glass unit, so it cannot fail in this way. But moisture between the main window and an interior storm window is a real issue. On an older window with an interior storm window, moisture trapped between the layers of glazing can condense on the colder outer window and potentially lead to deterioration.[3] If you see this, check the weatherstripping and the paint and putty on the main sash, and read how to maintain old wood windows. If the window is original wood, whether to repair or replace it is the question to settle first.

Stop and call a pro if

  • Several windows are fogged at once. A pro can judge whether it is a bad batch, a warranty claim or a sign the whole set is near the end of its life.
  • The wood around the glass is soft, stained or rotted. The moisture is coming from somewhere else, and the frame needs repair.
  • The window is on an upper floor. Reaching it safely means a ladder or scaffold you should not be on.
  • You are replacing the window, not just the glass. If the work is valued at $1,000 or more, a valid Virginia Contractor's License is required for the license category in which the contractor is to work.[4]
  • Water is dripping inside the room. That is a leak, not condensation.

Getting help in Virginia

More repair guides are on the Home Repair answers page, and local pros are listed under Doors and Windows on Loclis. If the window will not stay open, see how to fix a window that won't stay open.

When you are ready, describe the window and local pros will quote it in writing.

Common questions

Can I fix condensation between window panes myself?
Not for good. Once the seal has failed, the moisture between the panes cannot be prevented from forming, and the ideal solution is to replace the window.[^andersen] Drilling holes to let it dry, or sprays sold to clear the fog, rarely hold up, and they leave the glass unit unsealed. A pro can tell you whether the glass unit alone can be replaced.
Is moisture between the panes dangerous?
Not by itself. It means the window no longer insulates as designed, so you lose some comfort and energy efficiency, and the fog can leave a film or mineral spots on the inside faces of the glass that cannot be cleaned. It is a repair to plan, not an emergency.
What if the condensation is on the room side of the glass?
That points to indoor humidity, not a failed seal.[^andersen] In winter aim for 30 to 35 percent humidity,[^andersen] run the bath and kitchen fans, and open blinds during the day so warm air reaches the glass. A strip of condensation only around the edge can come from a metal component that touches both the outside and inside of the window.[^andersen]
What about moisture on the outside of the glass?
That is dew, caused by conditions outside, and it is not a sign the window is failing.[^andersen] It burns off once the sun is on the glass.
My old single-pane window has moisture between the glass and the storm window. Is that a failed seal?
Not in the same way, because there is no sealed glass unit. On an older window with an interior storm window, moisture trapped between the layers of glazing can condense on the colder outer window and potentially lead to deterioration.[^nps] Check for gaps and drafts around the window and look at the wood for paint failure.
Do I need a licensed contractor to replace a window or glass unit?
In Virginia, if the work you are considering is valued at $1,000 or more, a valid Virginia Contractor's License is required for the license category in which the contractor is to work.[^dpor-guide] Check the licence on DPOR's licence lookup and get the quote in writing.

Sources

  1. [1] Condensation on windows: What causes it and how to manage it, Andersen Corporation. Checked October 27, 2026.
  2. [2] High Performing Windows or Storm Windows, ENERGY STAR, U.S. Environmental Protection Agency. Checked October 27, 2026.
  3. [3] Preservation Brief 9: The Repair of Historic Wooden Windows, Technical Preservation Services, National Park Service. Checked October 27, 2026.
  4. [4] What You Should Know Before You Hire a Contractor, Virginia Board for Contractors, DPOR. Checked October 27, 2026.

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