What to do if PVC windows fog up

What does "fogging" of PVC windows mean?

Fogging is condensation forming on the glass surface or between the panes of a double-glazed unit. There are two main cases:

• Condensation on the interior glass surface (facing the room) — usually caused by high indoor humidity and poor ventilation.
• Moisture trapped between panes (inside the sealed unit) — a sign of a failed seal; moisture has entered the glazing cavity and the insulating unit needs repair or replacement.

Quick checks to identify the cause

1. Wipe the glass. If the moisture clears and reappears later, it is surface condensation.
2. Look for droplets or a foggy film between the panes — if present, the seal is compromised.
3. Feel the window frame edges for cold spots — cold edges can indicate seal or installation problems.

Immediate actions you can take

• Wipe the glass with a soft, dry cloth or microfiber to remove water.
• Check the sill and surrounding areas for water buildup.
• Increase ventilation: turn on bathroom/kitchen fans, open windows for brief airing several times a day.
• Use desiccant packs or a household dehumidifier in rooms with persistent humidity.

Adjustments and maintenance to reduce fogging

• Improve ventilation: regular airing, installing trickle vents or mechanical ventilation. Micro-ventilation on PVC windows lowers humidity without excessive cooling.
• Maintain indoor humidity at 40–60%. Use an electric dehumidifier if needed.
• Avoid drying large amounts of laundry indoors without ventilation.
• Inspect and replace worn seals — degraded rubber gaskets fail to prevent air and moisture ingress.
• Keep drainage holes and profiles clear from debris.

When fogging is inside the insulated glass unit (between panes)

Moisture inside the sealed unit is a sign of a broken seal. DIY attempts (drilling, heating with a hairdryer) are temporary and do not fix the root cause.

• Document the problem with photos and check your warranty from the manufacturer or installation company.
• Contact a professional glazing service: repair usually requires replacing the sealed unit or renewing the spacer and desiccant — specialists should perform this.
• Cost note: replacing the sealed unit is often more economical than replacing the entire frame. Choose high-quality spacers and desiccants when ordering replacements.

Prevention and correct usage

• Install trickle vents or a ventilation system in rooms prone to humidity.
• Keep stable indoor temperature; avoid large local cold zones near windows.
• Use short frequent airing (5–10 minutes) rather than long, slight openings in winter.
• Monitor indoor plants and occupancy — many plants and people increase humidity quickly.

When to call a technician

• You see fogging permanently inside the sealed unit.
• Frost or ice forms on the glass edges.
• You feel drafts, loose seals, or difficulty operating the window.

Frequently asked questions

Why do my windows fog up only in the morning?

Night-time temperature drops lead to cold glass; warm, moist indoor air condenses on the colder surface. Morning airing and reducing humidity help.

Can I dry the sealed unit myself?

Using a hairdryer or heater can remove surface moisture but won’t restore a failed seal. Professional replacement of the sealed unit is the lasting fix.

Does heating solve the fogging problem?

Heating evens out cold spots but does not reduce humidity. Proper ventilation and humidity control are necessary for a permanent solution.

Quick checklist

• Air rooms 3–5 times daily for 5–10 minutes.
• Maintain indoor humidity 40–60%.
• Check seals and drainage holes regularly.
• Use desiccants or dehumidifiers when needed.
• Call a specialist if fogging appears between panes.

Need step-by-step guidance for checking seals or a recommended service in your area? Provide your region and window model, and we will help.