The short answer
If the frame is sound and only the sealed glass unit has failed, replacing the unit is usually the sensible, cheaper fix. If the frame is rotten, warped, hard to open or simply worn out, new glass in an old frame is money poorly spent, and replacing the whole window makes more sense. The price difference on the page below shows what other homeowners actually paid for each job. The condition of the frame should decide it, not the misting alone.
How they differ
Misted window repair means replacing the sealed glass unit and keeping the existing frame. Double glazing is two panes separated by a spacer bar and sealed around the edge. When that seal fails, moist air gets in and condensation forms between the panes. It cannot be wiped away, because it is inside the unit. A fitter measures the old unit, makes or orders a new one, removes the beads or gaskets holding it in, and fits the new sealed unit in the same frame.
Window replacement means taking out the whole window, frame, sashes and glass, and fitting a new one. You can change the style, the frame material, the opening arrangement and the glazing specification, for example moving to triple glazing or a different type of glass. It is a bigger job, with more making good around the opening.
The key difference is what you end up with. A new unit gives you clear glass again, but the frame, hinges, handles and seals around it are as old as before. A new window gives you everything new.
Cost: what makes each more or less expensive
In general, replacing a sealed unit costs less than replacing a whole window of the same size. You are paying for glass and labour, not for a new frame, hardware and the work of removing and fitting a complete window. The real prices homeowners paid are shown separately on this page, so you can see how the two compare in practice.
For glass unit replacement, the main factors are:
- Size and number of units. Larger panes cost more, and several units in one visit are often better value per window than a single call-out.
- Type of glass. Toughened, laminated, obscured, tinted or low-emissivity glass costs more than plain clear glass.
- Access. Upper floors, awkward openings or the need for scaffolding or a hoist add cost.
- Fixing method. Some frames are easy to open up. Others have beads that are painted over or fragile, which takes longer.
For whole window replacement, the main factors are:
- Frame material. uPVC is generally the more affordable option. Aluminium and good-quality timber usually cost more.
- Glazing specification. Triple glazing costs more than double, and whether it pays back depends on your home and how long you will stay.
- Style and complexity. Sash windows, bay windows, bespoke shapes and heritage-style frames cost more than standard casements.
- Making good. Plastering, redecorating inside and repairing the sill or reveals can add to the bill.
- Number of windows. Doing several at once usually reduces the cost per window.
A cheaper job now is not always the cheaper job overall. If you fit a new unit into a frame that fails soon afterwards, you may pay twice.
Lifespan and upkeep
A new sealed unit should last for a long time if the install is good, but it is only as durable as the frame holding it. If the frame is in good order, the new unit can serve for as long as the original did. If the frame is tired, you may find gaskets perishing, drafts returning or hinges failing before the new glass has done its job. Check what guarantee comes with the new unit and whether it covers the installation as well as the glass.
A new window should give you the longest period without worry, because every part is new. Upkeep depends on the material. uPVC needs little more than cleaning and an occasional check of hinges and locks. Aluminium is also low maintenance. Timber needs regular painting or staining and attention to any damp or rot, but it can be repaired and kept going for a very long time if looked after.
In both cases, look for a written guarantee, and keep the paperwork. It matters if you sell the house, and if the seal fails again you will want to know who is responsible.
When to choose Misted window repair
Replacing just the glass is the better choice when:
- The frame is solid, with no soft or rotten timber, no cracking or serious warping, and the window opens and closes properly.
- The hinges, handles and locks work and the seals are in decent order.
- Only one or a few units have misted, and the rest of the windows are in good shape.
- You are happy with how the window looks and the existing frame suits the house.
- Your budget is tight and you want the clear view and insulation back without a bigger project.
- The property is listed or in a conservation area, where changing windows may be restricted and keeping original frames is preferable. Check with your local council first.
It is also a good fit if the windows are fairly recent and the failure looks like an isolated seal fault. In that case the original guarantee may still cover it, so check before you pay for anything.
When to choose Window replacement
A full replacement is the better choice when:
- The frame is rotten, split, warped or corroded, or the window no longer closes squarely.
- Several windows have misted. This often means the whole set is reaching the end of its life, and fitting new glass one by one can become a drawn-out expense.
- The windows are draughty, noisy or hard to open, and the glass is only one of the problems.
- Security is a worry, and the locks and hinges are outdated or cannot be upgraded.
- You want better thermal performance than the old frames and glass can offer, or you are planning wider work on the house and want it to match.
- You want a different style, material or opening arrangement.
Bear in mind that replacement windows in homes in England and Wales generally need to meet Building Regulations. This is usually handled by a registered installer or by notifying building control. Planning permission is not normally needed for like-for-like replacements in most houses, but it can apply to flats, listed buildings, conservation areas and some other cases, so check locally before you commit.
Questions to ask a tradesperson
- Is the frame in good enough condition to take a new unit, and how can you tell?
- Could the failed unit still be under guarantee, and who should I contact about that?
- What type of glass and spacer will the new unit have, and how does it compare with what I have now?
- Is the quote for glass only, or does it include removal, disposal, making good and VAT where it applies?
- If I replace the whole window, will you handle Building Regulations compliance and give me the certificate?
- What guarantee do you give on the glass, the frame and your workmanship, and is it in writing?
- If you find rot or damage once the old unit is out, how will you tell me and how will the price change?
- How long will the job take, and will you need access inside the house?
- Can you give me a quote for both options so I can compare them?