Your free quote, in seconds
Misted or failed double glazing? Measure the unit, pop your sizes into the calculator below and get an instant guide price, supplied and fitted. Every job is confirmed with a free, no-obligation exact quote.
Price your replacement unit
Pop in your sizes for an instant guide price. Not sure how to measure? Send us a photo on WhatsApp and we'll talk you through it.
Double glazed unit cost calculator
Measure the visible glass, add 10mm each way, and we'll give you an instant guide price, supplied and fitted.
Enter a width and height to see your guide price.
Estimated: per unit, fitted
That's a big unit, so call us on 07706 188127 for a price.
- All conservatory glass, door glass and any window glass less than 80cm from the floor must be toughened safety glass.
- Most units are no more than 100cm wide. If your sizes fall outside the calculator, call us for a price.
- Guide price only, subject to survey. Every job is confirmed with a free, no-obligation exact quote before any work is booked.
Why do double glazed units fail?
A double glazed unit is two panes of glass with an insulating gas, usually argon, sealed into the gap between them. The seal around the edge keeps that gas in and moisture out. Once the seal fails, mist creeps in and the unit's performance falls away.
A healthy unit
Two panes, a dry insulating gap and a tight edge seal quietly doing its job.
The seal breaks down
Sunlight, weather and years of expansion and contraction wear the seal until moisture finds a way in.
Mist you can't wipe
Condensation forms between the panes, out of reach from either side. That's the sign the unit has failed.
What causes a seal to fail?
Seal deterioration
The edge seal simply ages with sunlight, temperature swings and weather. This is the most common cause of all.
Thermal expansion
Daily heating and cooling makes the glass and spacer expand and contract, putting stress on the seals.
Poor manufacturing
Inferior materials or defects during production can cause seals to fail years earlier than expected.
Improper installation
A twisted frame, a unit fitted under stress or inadequate drainage all put extra pressure on the seals.
Building movement
Settling foundations or structural movement can distort the window frame and stress the sealed unit.
Physical damage
Impacts or excessive vibration can compromise the edge seal or crack the glass itself.
Water exposure
Blocked drainage or perished window seals leave persistent moisture sitting against the unit's edge.
Signs your unit has failed
- Condensation or mist between the two panes that can't be wiped away.
- A cloudy or hazy appearance inside the unit.
- Rooms feeling colder as the thermal insulation drops off.
- In some cases, visible deterioration or a gap around the edge seal.
How long should a unit last?
A quality double glazed unit typically lasts 15 to 30 years. What makes the difference:
- The quality of the unit itself.
- Local climate and sun exposure.
- The quality of the original installation.
- How well the frames and drainage are maintained.
Seeing mist between your panes? That almost always means the seal has failed, and the practical fix is a new sealed unit. If your frames are still in good condition, only the glass needs replacing, which costs a fraction of a whole new window.
Don't replace, repair!
At Window and Door Doctor, we pride ourselves on our reputation across Bridgwater and the surrounding areas as a leading expert in window and door repairs and installations. With over a decade of experience serving domestic and commercial clients in the South West, you can trust us for expert advice, competitive prices and professional customer service.
Our mission is to help customers understand the benefits of repairing their windows and doors rather than immediately replacing them. By fitting new glass into your existing frames we can breathe new life into your windows and doors, restoring their function and looks while saving you money and reducing your environmental impact.
Areas we cover
Bridgwater • Taunton • Glastonbury • Cheddar • Weston-super-Mare • Congresbury • Watchet • Minehead • Wellington • Chard
Happy with your guide price?
Send us your sizes and a photo or two, and we'll confirm everything with a free, no-obligation exact quote.
Send us your sizes
Pop the sizes from the calculator into a message, tell us if you need toughened glass or Georgian bars, and we'll come back with an exact quote. Or call us on 07706 188127.