Updated June 2026 · CW Doors & Windows
Can double glazing stop condensation? The honest answer
Double glazing reduces internal condensation dramatically — but it never eliminates it. And external condensation on the outside of A-rated glass is actually a sign the windows are working. Here's the diagnosis.
Internal condensation (on the inside of the glass)
Caused by warm humid indoor air hitting a cold pane. Modern A-rated double glazing keeps the inner pane warm enough to prevent this in most rooms.
If you still get internal condensation after installing new double glazing, the cause is humidity, not the glazing — kitchen extractors, bathroom fans, and trickle vents need to be working.
Condensation between the panes
This means the sealed unit has failed and the desiccant is saturated. No repair — the unit needs replacing. £150–£300 per window in Leicester.
External condensation (on the outside of the glass)
Counterintuitive but true: A-rated glass is so well insulated that the outer pane stays close to ambient temperature, and on cool clear mornings dew forms on the outside.
This is proof the windows are working — not a defect. It usually clears within an hour of sunrise.
What actually fixes condensation
Trickle vents open. Bathroom extractor working. Cooker hood vented externally. Tumble dryer vented. Wet washing not hung on radiators.
If condensation persists, a positive input ventilation (PIV) unit costs £400–£700 and cures most chronic condensation problems.
When condensation means something has failed
Condensation on the room side of the glass is usually about humidity and ventilation. Misting between the two panes is different: it means the seal in the sealed unit has failed and the unit needs replacing.
We can replace failed units or, where the frames are also past their best, fit new A-rated windows from £450. Trickle vents can be specified on new windows to help rooms that suffer badly from condensation.
Get a free written quote
Family-run Leicester installer, 40+ years, 10-year insurance-backed guarantee. Clear, itemised written quotes.
Request your free quoteFrequently asked questions
Get your free quote
No pressure, no salesmen, itemised in writing.