Fog or water droplets on an impact window mean one of three things: normal condensation on the surface, a failed seal inside an insulated unit, or a leak at the frame. Each looks a little different and each has a different fix. Here is how to tell them apart.
1. Condensation on the outside of the glass
On a humid South Florida morning, the outside of a Low-E impact window can fog up the way a cold drink sweats. This is normal and is actually a sign the glass is doing its job: the Low-E coating keeps the inside pane cool, so the outer surface is cooler than the humid air. It clears as the sun comes up. No action needed.
2. Condensation on the inside of the glass
Moisture on the room side of the glass means indoor humidity is high. It is common with new, tight-sealing impact windows in homes that previously leaked air through old frames. Run the air conditioner on a dehumidify setting, use bathroom and kitchen exhaust fans, and check that the AC drain is clear. Persistent interior condensation is a humidity problem, not a window problem.
3. Fog between the panes
If the haze is inside the glass and you cannot wipe it from either side, the seal on an insulated laminated unit has failed and moisture has entered the air space. This only happens on insulated units; a plain laminated impact window has no air space and cannot fog internally. A failed seal does not affect the impact rating, but the unit loses its insulating value and looks bad. The fix is replacing the glass unit, which may be covered by the manufacturer’s warranty depending on age and terms.
4. Water at the frame or sill
Water on the sill, stains on the drywall below a window, or drips at the frame corners point to a flashing or sealant problem, not the glass. This needs attention: check the exterior caulking and weep holes, and call your installer. Under the Elevate workmanship warranty, installation leaks in the first year are corrected at no charge. Our warranty.
Quick diagnosis
| Where is the moisture? | What it means | What to do |
|---|---|---|
| Outside surface, mornings | Normal; Low-E glass is working | Nothing |
| Inside surface | High indoor humidity | Dehumidify, run exhaust fans, check AC drain |
| Between the panes | Failed seal on an insulated unit | Replace the glass unit; check warranty |
| Frame, sill or wall below | Installation or sealant issue | Inspect caulking and weep holes; call the installer |
Preventing seal failure
- Choose a quality manufacturer; seal durability varies by brand
- Keep weep holes clear so water never sits in the frame
- Do not pressure-wash windows at close range
- Avoid aftermarket window film on insulated units, which can overheat the glass and stress the seal
Frequently asked questions
Why are my impact windows fogging up on the outside?
Humid air is condensing on a cool outer surface because Low-E glass keeps the inner pane cool. It is normal and clears as the day warms.
Why is there fog inside my impact window?
Fog between the panes means the seal on an insulated unit has failed. The glass unit should be replaced, often under warranty.
Do laminated impact windows fog?
Laminated glass with no air space cannot fog internally. Only insulated laminated units have a seal that can fail.
Is condensation covered by warranty?
Surface condensation is not a defect. Fog between panes from a failed seal is typically covered by the manufacturer’s warranty, subject to its terms.
Does fogging mean the window is no longer impact-rated?
No. The impact rating comes from the laminated pane, which is unaffected by a failed insulating seal.