THE SHORT ANSWER
Condensation trapped between the sealed panes of an insulated window can indicate a failed glass seal. First distinguish it from moisture on the room-facing or outdoor surface. Record what you can see safely and contact the window maker or a glazier. Surface cleaning cannot reach moisture inside a sealed glass unit.
Before you try anything
Stay on the floor or ground. Do not lean out, climb, remove a sash, pry glass, drill a pane or heat it to clear the fog. Keep people away from cracked, loose or broken glass and arrange professional help. Do not open a window that will not stay securely supported.
Before you begin
For intact household windows with suspected moisture between sealed panes. This is an observation guide, not a glass-replacement procedure. Separate storm windows and removable or hinged secondary glass panels can have different condensation causes. Identify the construction before calling it seal failure. Rain entering the room belongs to a separate leak check.
A dry soft cloth, the window brand or existing paperwork, and a phone for photos. Note the room, date, weather and which pane appears affected. Use labels already visible from a safe position; do not remove components to find a serial number.
In a rental, report the problem to your landlord or property manager before making repairs. Building rules and local requirements vary.
Work through the checks
- 01
Identify the window type
Check existing documents for a sealed insulating-glass unit, a separate storm window or an additional hinged panel. If uncertain, take a wide photo for the manufacturer instead of dismantling it.
- 02
Check the room-facing surface
On intact, easily reachable glass, wipe a small patch gently with a dry soft cloth. If that patch clears, some moisture is on the room side. More than one surface can be affected.
- 03
Observe the outdoor surface safely
From ground level, look for exterior droplets or haze that changes as the day warms. Do not reach out of an upper window to wipe the far side. Inaccessible glass is a reason to leave the location uncertain.
- 04
Record persistent trapped haze
Photograph the same window at different ordinary times. Note whether room-side wiping changes it and whether the apparent haze remains between sealed panes. A photo documents the symptom; it cannot establish the condition of every seal.
- 05
Ask for a product-specific assessment
Send the observations through your chosen service channel or tell the landlord. Ask whether the affected insulating glass or sash can be replaced, what condition the frame is in, and which warranty terms apply. Do not assume the whole window must be replaced.
What your result means
These observations help choose a next step. They do not confirm a diagnosis.
| What you notice | What it tells you | Next step |
|---|---|---|
| Moisture wipes off indoors | Room-side condensation is present | Use the related indoor-condensation guide; record any separate trapped haze. |
| Exterior dew changes through the day | Outdoor conditions may explain it | Observe safely; exterior moisture alone does not establish seal failure. |
| Haze remains inside a sealed unit | A glass-seal problem may be involved | Ask the manufacturer or glazier to confirm the location and repair options. |
| Moisture behind a hinged secondary panel | This may not be the sealed cavity | Use the exact product manual before drawing a conclusion. |
| Cracked glass or rain entering the room | A separate damage or water-entry issue exists | Keep clear and arrange appropriate help. |
Know what happens next
Check the outcome
A useful outcome is a clear record of which surface is affected, or an honest note that you cannot tell. If service replaces a glass unit or sash, ask how to check the completed work and what warranty applies. A temporarily clear pane does not prove the original seal has recovered.
When to call a professional
Stop home checks for cracked glass, a loose pane, an unsupported sash, inaccessible exterior glass or water entering the room. Contact a qualified window professional. In a rental, report the observation before arranging alterations.
Take useful notes with you
A short record makes it easier to explain the problem to a landlord, technician, or responder. Do not collect notes during an emergency.
Notes stay in this page until you leave or reload. Download a copy to keep them. They are not sent to us.
Common questions
Will a dehumidifier clear condensation between sealed panes?
Reducing indoor humidity can help room-side condensation. It does not repair a failed sealed-glass unit. Pella distinguishes sealed-pane moisture from condensation behind its hinged glass panel.
Does fog mean I need an entirely new window?
It calls for an assessment. Pella identifies replacement of the affected insulating glass for seal failure; available glass, sash or full-window options depend on the product and frame condition. Ask before ordering.
Can I drill a small hole or use a hair dryer?
Do not drill, pry or heat the glass for this check. Ask the manufacturer or a qualified glazier about an approved repair. Clearing the appearance would not by itself verify restored performance.
Sources & scope
This is a desk-researched guide, not a hands-on test or an on-site diagnosis. A licensed tradesperson has not independently reviewed this edition. Follow your product’s manual and local requirements.
- Andersen — Window condensation 101
Read 2026-10-15. Distinguishes interior, exterior and between-pane condensation; sealed-cavity moisture indicates seal failure.
- Pella — Condensation Owner’s Manual
Read 2026-10-15, pages 3 and 6. Sealed insulating glass may need replacement; a Lifestyle hinged glass panel is a distinct case.
- Andersen — Condensation on Exterior Glass
Read 2026-10-15. Exterior dew can occur with changing outdoor conditions and commonly evaporates through the day.
- Related guide: Condensation inside windows
For moisture on the room-facing surface, rather than trapped inside sealed glass. Internal Home Fieldnotes reading, not independent technical evidence.
- Related guide: Window leaks during rain
For actual water entering the room during rainfall; do not recreate a known leak. Internal Home Fieldnotes reading, not independent technical evidence.
Published 2026-10-15 · Our editorial policy · Report a correction