Condensation Between Double Glazed Windows — What’s Causing It and How to Fix It
If you’ve noticed a foggy or hazy patch inside one of your windows — the kind that won’t wipe away from either side — you’re looking at condensation trapped between the glass panes. It’s one of the most common double glazing problems in UK homes, and the good news is that it’s fixable with a replacement sealed unit.
This guide explains exactly what’s happening, why DIY approaches fall short, and what the permanent fix actually involves.
Why Is There Condensation Between My Double Glazing?
A double glazed unit is made up of two panes of glass separated by a hermetically sealed cavity. That cavity — typically filled with argon gas or dry air — is what gives the window its thermal performance. The argon slows heat transfer between the warm room-side pane and the cold outside pane, which is why double glazing is significantly warmer to the touch than single glazing and why it reduces heat loss.
The seal around the perimeter of the unit keeps that cavity intact. Over time — typically 15 to 25 years, though sometimes sooner in cheaper units or particularly exposed positions — this seal degrades. The main culprits are UV radiation from the sun, and temperature cycling: the constant expansion and contraction of the glass as it heats and cools throughout each day gradually breaks down the edge bond.
Once the seal fails, moisture from the surrounding atmosphere enters the cavity. When the temperature inside the cavity drops below the dew point — the temperature at which water vapour condenses into liquid — that moisture becomes visible as condensation on the inner surfaces of the two panes.
This is what you’re seeing: moisture inside the sealed unit, condensing on glass that you can’t reach from either side of the window.
Is It Actually Condensation — or Something Else?
Not all window condensation is the same problem. It’s worth being clear about where exactly the moisture is appearing before drawing conclusions.
Condensation between the panes (inside the unit). This appears inside the sealed cavity — foggy, hazy, or as visible droplets on the inner glass surfaces. You cannot reach it from inside or outside the property. This is seal failure. The unit needs replacing.
Condensation on the inside surface of the glass. A thin film of moisture on the room-facing glass face in cold weather, most common in kitchens, bathrooms, and bedrooms. This clears as the room warms up. It indicates a ventilation issue — not a window fault — and is addressed by improving airflow, not replacing glass.
Condensation on the outside surface. Moisture on the outer face of the glass on clear, cold mornings. This is actually a sign the window is working well. The outer pane is cold because the argon-filled cavity is effectively blocking heat transfer from inside. No action is needed.
If the moisture is inside the unit and won’t clear, you have a seal failure. The rest of this guide applies to you.
Can You Remove Condensation from Between Double Glazed Panes?
Most people searching for how to get rid of condensation in between double glazed windows find the same answer: it cannot be done. Once moisture is inside the sealed cavity, it cannot be removed without replacing the unit.
The cavity is hermetically sealed by manufacture — airtight and moisture-tight by design. When the seal fails, moisture enters through microscopic gaps in the edge bond. There is no way to extract that moisture, restore the seal without opening the unit, or return it to its original dry, gas-filled state other than fitting a new sealed unit.
Some temporary measures circulate online. Neither of the most common options offers a lasting fix.
Why DIY “Fixes” Don’t Work
Drilling small holes in the unit. The idea is to drill into the cavity, introduce a desiccant to absorb moisture, and allow the unit to breathe. In practice, this permanently removes the argon gas fill and opens the cavity to external air — the unit’s thermal performance is reduced for good. The condensation may temporarily appear less severe, but the underlying seal failure has not been addressed, and the energy-saving performance of the window does not return.
Window “restoration” or re-sealing services. Some companies offer a process involving drilling, drying, and injecting a gas or sealant. Results vary, and the longevity is generally poor. The edge seal that failed once is not structurally restored by this process, and repeat failure within a few years is common. For most homeowners, a new factory-sealed unit with a fresh guarantee is the more reliable and cost-effective long-term outcome.
The Only Permanent Solution: A New Sealed Unit
The good news is that fixing a failed sealed unit does not mean replacing the entire window. In the vast majority of cases, the frame — whether uPVC, aluminium, or timber — is perfectly fine. Only the glass unit itself needs to go.
PTF Glass makes replacement double glazed sealed units to measure. You send us the sizes — we’re happy to explain how to measure accurately — and we manufacture a matched replacement to the exact dimensions, with the same glass type and spacer as the original. You then collect the finished unit from our Bramley premises (LS13 4EN) or we can arrange delivery. The new unit is fitted into your existing frame by you or your own glazier; the frame itself is not disturbed.
Made-to-measure sealed units are typically ready within 7–14 working days, depending on the unit specification and glass type.
For a full breakdown of what to expect on cost, see our guide to the cost of replacing a double glazed unit.
How Long Can You Leave It?
Condensation between the panes is not an emergency, but it worsens progressively and does not self-correct.
In the early stages, you may see occasional fogging that partially clears in warm, dry conditions. As the moisture cycle continues, mineral deposits begin to build up on the inner glass surfaces. Eventually this causes permanent staining — a cloudy, whitish haze that remains visible even on warm, clear days and cannot be cleaned away. At this stage the window looks permanently impaired regardless of conditions.
Beyond appearance, a failed unit loses its thermal performance. The argon gas escapes through the failed seal, and the window’s insulating value drops. Over a heating season, this contributes measurably to heat loss — particularly noticeable if multiple units in the property are affected.
In timber-framed windows, moisture from the condensation can also accelerate frame rot at the cill and lower rails over time. Addressing the glass unit failure before this stage avoids more significant repair costs later.
Get a Price from PTF Glass
PTF Glass makes and supplies made-to-measure replacement sealed units across Leeds and the surrounding area — for homeowners and the trade alike. We make the glass to your exact sizes; you or your own installer fit it. Pricing is transparent and confirmed before you order.
We serve Leeds and West Yorkshire including Morley, Rothwell, Armley, Headingley, Roundhay, Horsforth, Pudsey and Bramley, plus Wetherby, Wakefield, Castleford and Pontefract.
If you’ve noticed condensation between your panes, 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. Collect from Bramley (LS13 4EN) or ask about delivery.
Looking for the replacement glass in your area? See our misted unit replacement service areas page.
If your double glazing is visibly wet between the panes rather than just hazy, see our guide to what to do when your double glazing is wet inside.
Frequently Asked Questions
How long does a double glazed unit typically last before the seal fails?
Most quality double glazed units have a working life of 15–25 years before seal failure becomes likely. Budget units, units in south-facing or particularly exposed positions, and units that were not made or fitted correctly may fail sooner. Age is the most common factor by some distance.
Will condensation between the panes go away on its own?
No. Once the hermetic seal has failed, moisture continues to enter the cavity whenever external humidity is higher than the cavity’s current state. The problem does not self-correct. It typically worsens over time as mineral deposits accumulate on the inner glass surfaces, eventually causing permanent staining.
Does insurance cover failed sealed units?
Most standard home insurance policies treat double glazed unit failure from wear and age as a maintenance issue rather than accidental damage, and do not cover it as standard. Some policies include glazing cover — it is worth checking your policy documents. If your units are within the original manufacturer’s guarantee period, check that first.
Can I just get a new glass unit rather than the whole window?
Yes — in most cases this is the correct and most cost-effective approach. A replacement sealed unit is a new piece of glass made to the exact size of the failed one, then fitted into your existing frame. The frame is retained. PTF Glass makes the replacement unit to measure; you or your own glazier fit it.
Is condensation between the panes a sign I need to replace the whole window?
Not necessarily. Condensation between the panes indicates seal failure in the glass unit, not in the frame. If the frame is in good condition — no rot, no significant warping, no failed frame seals — a new sealed unit is all you need. If you’re unsure whether your frame is sound, your glazier can confirm at the point of fitting.
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: