Double Glazing Wet Inside — What It Means and What to Do
If your double glazing is wet or fogged on the inside — moisture you can see between the panes but cannot wipe away — the sealed unit has failed. It is one of the most common double glazing faults in UK homes. Here is what is happening, and what to do about it.
Why Is My Double Glazing Wet Inside?
The moisture you are seeing is trapped between the two panes of glass that make up the sealed unit. A double glazed unit is manufactured with a hermetically sealed cavity between the panes — usually filled with argon gas or dry air — and a perimeter seal that keeps moisture out. When that seal degrades, moisture enters the cavity and condenses on the inner surfaces of the glass.
Seal failure is typically caused by age, UV degradation, and the repeated expansion and contraction of the glass as it heats and cools throughout each day. Most double glazed units have a working life of 15–25 years before seal failure becomes likely. Budget units, south-facing windows, or units that were not made or fitted correctly may fail sooner.
Is It Condensation, or Actual Water?
Both can appear — and both point to the same underlying fault.
In the early stages of seal failure, the moisture usually shows as condensation: a hazy, foggy film on the inner glass surfaces that forms when the air temperature inside the cavity drops. In more advanced cases, you may see visible water droplets running down the inner glass, or a small pool forming along the bottom edge of the unit.
It is worth distinguishing this from two other types of window moisture that are not caused by a failed unit:
Condensation on the inside surface of the glass. A film of moisture on the room-facing glass in cold weather, most common in kitchens, bathrooms, and poorly ventilated rooms. This clears as the room warms up and is a ventilation issue, not a glazing fault.
Condensation on the outside glass surface. Moisture on the outer face of the glass on cold, clear mornings. This is normal and actually a sign the window is performing well. No action is needed.
If the moisture is between the panes and won’t clear, the unit has failed — and the sections below apply.
Will It Clear on Its Own?
No. Once the hermetic seal is broken, the moisture cycle accelerates rather than reverting. In warm, dry conditions some of the moisture may partially evaporate, but the unit does not return to its original sealed state.
Each cycle of condensation and evaporation leaves mineral deposits on the inner glass surfaces. Over time, these deposits form a permanent cloudy staining that remains visible even on warm, dry days and cannot be cleaned from the inside or outside. The appearance worsens month by month.
What Happens If You Leave It
There are practical consequences to leaving a failed unit in place beyond the worsening appearance.
Loss of thermal performance. The argon gas that provides the unit’s insulating value escapes through the failed seal. A unit that has lost its gas fill performs closer to single glazing than properly sealed double glazing, contributing to heat loss and higher energy bills. This effect is more significant over a full heating season, particularly where several units in the property are affected.
Permanent glass staining. As described above, mineral deposits from the condensation cycle eventually cause irreversible discolouration of the inner glass surfaces. A new unit at this stage still gives you a clear pane — but it is worth acting before reaching this point simply on the grounds of cost and disruption.
Frame deterioration in timber windows. In properties with timber window frames, condensation moisture that runs down from a failed unit can accelerate rot at the cill and lower rails over time. Addressing the glass unit before this stage avoids more significant repair costs later.
The Fix: A New Sealed Unit
The only permanent fix for moisture between double glazed panes is a new sealed unit. In almost all cases, only the glass unit needs replacing — the frame (whether uPVC, aluminium, or timber) is retained.
PTF Glass makes the replacement unit to measure: send us the sizes, we manufacture a matched, factory-sealed unit, and you collect it from Bramley (LS13 4EN) or we arrange delivery. The new unit is then fitted into your existing frame by you or your own glazier.
Typical costs range from around £60 for a small top-opener casement to £320 for a larger patio door panel for the supplied unit. See our full pricing guide for replacement double glazed units for a size-by-size breakdown.
Made-to-measure units are typically ready within 7–14 working days.
How PTF Glass Can Help
PTF Glass makes and supplies made-to-measure replacement sealed units across Leeds and the surrounding area — for homeowners and the trade. We make the glass to your exact sizes; you or your own glazier fit it. You get a fixed price for the unit before you order, with no obligation. We serve Leeds and West Yorkshire including Morley, Rothwell, Armley, Headingley, Roundhay, Horsforth, Pudsey and Bramley, plus Wetherby, Wakefield, Castleford and Pontefract.
Send us your sizes for a price on a made-to-measure replacement unit. Every unit carries the Eurocell 10-year manufacturer guarantee plus PTF Glass’s own 5-year guarantee against sealed-unit failure.
Also useful:
- Condensation between double glazed windows — causes and solutions in full
- Misted unit replacement near me — where PTF Glass supplies
Frequently Asked Questions
Will the moisture between my panes go away if I leave it?
No. Seal failure is not a self-correcting problem. The moisture that enters the cavity does not leave through the same route, and each temperature cycle progressively worsens the staining inside the unit. The only fix is a new sealed unit.
Is double glazing wet inside serious?
It depends on the stage. Early-stage seal failure is a cosmetic and thermal performance issue — not dangerous, but getting progressively worse. In timber-framed windows, moisture from a long-standing failed unit can contribute to frame deterioration over time. It is worth addressing sooner rather than later, but there is no immediate emergency.
Can I just get a new glass unit, or do I need a whole new window?
In the vast majority of cases, just the glass unit needs replacing and the frame is retained. PTF Glass makes the replacement sealed unit to measure; you or your own glazier fit it into the existing frame. This is much simpler and more cost-effective than full window replacement, unless the frame itself has also failed.
Misted double glazing — areas we supply across West Yorkshire
We make replacement sealed units to measure for homeowners and installers across Leeds and West Yorkshire. Areas we regularly supply include: