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Do you know what to look out for when buying double glazing?

double glazing

Planning a window upgrade in a bid to boost the energy efficiency and warmth of your home?

Double glazing isn’t cheap. In fact, if you were to replace all the double glazed windows in your house, it could cost as much as £6,000 or more. So you’ll want to make sure you’re making the right choice.

Double glazing decisions

We recently surveyed 2,239 Which? members and double glazing customers about their experiences with the company they used in the past five years.

Their ratings of well-known companies Anglian, Everest and Safestyle, and independents, showed a 30% difference between the best and worst double glazing companies.

But we also discovered that more than a third of members only got one quote for their double glazing. This could be because they had used the company before, or because it was recommended to them by a friend.

Either way, I was quite surprised – the more quotes you get, the better chance you have of choosing the right company and getting the best price.

We’ve also heard of instances of double glazing companies quoting a high price, and then dropping it dramatically over the period of the sales visit. Don’t let this sway you to sign on the spot – take your time to compare quotes.

It’s also worth taking a look at our double glazing prices page before getting quotes to find out how much different types of double glazing is likely to cost – the more information you are armed with, the less likely you’ll overpay.

Beware of the contract

Once you’ve chosen a firm, it’s important to know what to look for when it comes to signing the contact and your rights when buying double glazing in general.

If you buy standard-sized double glazing from a door-to-door trader, over the phone or online, they are legally obliged to provide you with certain information in writing, such as a description of the goods/services, the total price (inclusive of any additional charges known at the start), when the goods/services will be provided and your rights to cancel within 14 days, all of which they must adhere to.

However, in some circumstances, the company isn’t bound to provide as much detail, and you won’t have the same right to cancel. This applies when you’re getting made-to-measure double glazing, or enter into an ‘on-premises contract’.

This includes a situation where a trader has discussed the contract at your home, but you agree to enter into it at a later date, which applies to a lot of home improvement projects. What they do provide in writing is still legally binding, so ask for as much as possible. Some traders will also still offer a right to cancel, so check the contract.

What have your experiences with a double glazing company been like? Have you ever had a bad one?


We’ve used DG companies three times. It’s always great fun, because without exception the first price quoted is so silly it almost defies belief. Then watching the rigmarole, the ‘phoning the boss, the ‘last possibility’ offer and so on provides a great afternoon’s entertainment. We will always have got at least four quotes, then prepared a mental cost of what we think the jobs should cost. And we’ve never failed to achieve what we wanted. But we have the time and energy to do it.

They’re not the only people who use the technique. Buying a new gas boiler was similarly entertaining, with the local chap’s price being the basis for all the negotiations. But some folk find it hard to believe we got the best price from British Gas. Not initially – BG’s price was more than twice that of the independent’s – but through our use of the same tactics as theirs (delaying, obfuscation, needing to consult the other half and so on) BG not only came down to the best offer but threw in some other goodies as well. The same thing happened when we had air conditioning installed.

This is very sad, because some people do undoubtedly sign on the dotted line at the first offer. What is really happening, in fact, is that the salespeople for these companies are actually operating a form of scamming. And perhaps it’s time for Which? to look at the fact that not all scams are instituted by furtively dressed ne’re do wells lurking in dark corners of Vladivostok cafes. Whenever you buy a high priced home improvement it’s a battle, fraught with deception and emotional lies.

Ian does not say who he went with but my premise is that I do not do business with companies who use this sort of sales tactic. And as for British Gas with a back-catalogue of naughty stories.

This was first off the heap and look at the comments particularly.

It strikes me that if the first price you offered was legally the only offer you could make then this tactic would be redundant. A dated timed offer being sent via smartphone to smartphone or emailed to the customer then and then, or to a third party with the electronic facilities would be proof positive. Any subsequent lower offer in the next week deemed to be a contravention and a substantial penalty becomes due to the householder.

A few high-profile cases on TV and everyone would be aware of the opportunity to fight and profit from these tactics.

We had a visit from that company who’s sale pitch at the time was ‘you buy one you get one free’, I guess everyone knows who I am referring to. Anyway after the rep had done his pitch he came up with a quote of £11000, after getting back up off the floor he could see I was not impressed, so then came all the usual tactics of ring the head office in front of you bla, bla,bla. Needless to say he never got the business or would never have my business with those scam tactics. Eventually I had new ‘A’ rated glass and pvc windows and doors all round for half the price he quoted. Moral never ever sign at the first quote if the company cannot come up with a decent honest quote move on and keep moving on until you secure what you had budgeted for.

Mike Hindson-Evans says:
21 October 2016

Nearly twelve years after buying our house, and over ten years after selecting Safestyle to install (in effect) a complete set of windows and doors in a five-bedroom house, we continue to be very pleased with our choice. Over the years, four panes “blew” and were replaced, without quibble, under the ten-year warranty. All bar one of the “blown” panes were in bathrooms.

Maybe we were lucky (which is why the WHICH? survey aggregates so many other views) but I just wanted to record a counterpoint to the overall review.


I had Safestyle install my French doors. Now two sets of doors later replaced under warranty as they never ever closed properly now the screw heads are breaking and popping out of the hinges the screws are half the size of the hole that the hinges allow for, and the doors are now impossible to close. Yes cannot close them as they have dropped so much. I am going to go elsewhere to get new doors. You get what you pay for. But the front door installed by them is still going strong.


has interesting information and seems to be up-to-date

Helen Smith says:
23 October 2016

I have had 3 double glazing companies come to give a quote. From the outset they were advised that I was not buying that night but wanted a quote in writting. I was advised that whatever price I was quoted would be fixed for 12 or 15 months. Despite this the sales persons manager on all 3 different occassions tried to get me to buy that night, I had phone calss for several weeks from one of the companies offerring me more and more discount. I repeatly asked for my written quote but have yet to receive a written quote from any of the companies .

I did receive a written quote from CR Smith and because of this and the salesman who accepted that I was not going to buy on that night,i purchased my windows from them. Their total quote was higher than the other 3’s “if I place the order tonight” quotes but I had no pressure to buy on the night.

About 20 years ago we had several quotes for installing double glazing that ranged from £15,000 to over £30,000.

Rather staggered at the cost, we eventually used a local guy who got all his work from word-of-mouth for £6500 with a 5-year guarantee. He did a brilliant job. Several of the larger panes needed replacing and a couple of openings adjusting after about 15 years at a cost of around £700.

So shop around.

I had double glazing installed over 15 years ago and have been very happy with it. A friend offered to fit it at no cost (but I insisted) and I made the tea and held things for him. It was an easy job since I was living in a bungalow, so no scaffolding towers and ladders.

None of the units have become misted. I have seen many examples of misted panels in other homes, sometimes soon after installation. Price does not seem to be a factor.

I’m looking at replacing the double glazing in my present home and will look for recommended traders, but the big uncertainty is how to ensure that the panels will have a decent life. Obviously a long guarantee is useful but with double glazing now well established, why are misted panels so common?

We had Crittal steel windows – awful. Wet, cold and black mould. We don’t like uPVC so opted for timber frames, made to order (Crittal windows were odd sizes) and factory painted. That was about 10 years ago. We used a local firm to install then and they made two suggestions; rectangular leaded light and tiled “creasings” – quarry tiled ledges instead of timber. we would not have thought of either but both worked really well. We have, in that time, had 3 panels (out of 37) replaced because of internal condensation from leakage. I was told that installing the panels to ensure a gap is left at the bottom helps prevent the seals sitting in any water that might accumulate.

Aluminium windows and doors were probably worse for condensation. I was not happy with installing UPVC but not having to do any maintenance other than washing has changed my mind. Tiled window ledges make sense because that removes one of the main weaknesses of wooden windows. I want to replace my windows in the next year or so because the present ones have only an 8 or 10 mm air gap and although the wood is sound, the south facing cills are not in wonderful condition. I cannot tell whether any of the existing units have been replaced but three out of four panes in a bathroom window show signs of failure. Fortunately it’s not as obvious with obscure glass.

I learned that good installation is vital for various reasons. The glass panel gives rigidity to UPVC so careful packing is needed to stop doors sagging and sticking in their frames.

I had sliding patio doors replaced and was intending to use timber faced as the originals, but had no success in finding them at a realistic price. I went for aluminium, powder coated to match the timber colour. The have now been in 4 years and have been all I wanted – no condensation, frames not chunky. I might have chosen aluminium windows to minimise maintenance although I am a fan of wood.

I had forgotten that modern aluminium windows overcome the condensation problem, presumably to greatly reduce heat transfer from inside to outside. Being a late adopter has its advantages. Powder-coated aluminium is great provided water does not get in. There might be scope for development – maybe powder-coated anodised aluminium, which is used in other applications.

The usual way to colour anodised aluminium is to effectively dye the oxide surface before it is finally finished.

Indeed. Aluminium is a very reactive material that would oxidise very rapidly but for a thin oxide coating that adheres very tightly, unlike rust that forms on steel. Unless colouring provides additional protection it probably does not matter if the metal is then powder coated.

Generally paint will adhere to aluminium metal better than to an anodised coationg which is glass smooth. There are a whole range of anodising colours available. The anodising process is where raw aluminium is placed in a bath of electrolyte and current passed to build up a controlled thickness of aluminium oxide. The oxide is porous, which allows a colouring agent to enter the surface. Usually, from what I recall, it is then treated with hot water that closes the porous cells to give a smooth sealed surface that is highly effective in preventing corrosion.

Polyester powder paint is normallyused for exterior applications, electrostatically applied to aluminium and heated to form a very durable and protective coating

Architectural aluminum, for example, is finished in both ways, depending on the appearance required.

I wonder how often we tell each other things we already know, Malcolm 🙂 I’m sure we both know about etching primers for aluminium, galvanised steel, etc.

An advantage of being a member of a society is that people are often keen to offer skills and facilities. At one time I was getting powder coating done free or at cost for our charity.

I will take great panes to remain on the topic of double glazing.

wavechange, this is not a private conversation but maybe others who read comments would like an explanation of what is being discussed. 🙂

The treatments available for aluminium double glazing may well crop up if someone here goes out to source new windows.

My thoughts entirely, Malcolm. I like it best when Conversation is inclusive. We never know who might be reading and find technical details valuable whatever the subject. I would not like to see any aspect of Which? Conversation side-lined to a different channel.

Better ways of identifying sub-threads [font, point size, spacing, positioning] might help with presentation of Conversations so that people who don’t want to travel along the branch lines can more easily stay on the main lines.

My house has 68 double glazed window panes and not a single one is misted. They were made in 2002 by John Fredericks Plastics Limited, Huddersfield and fitted by Starlight Windows of Newton Aycliffe, and they are up to 1.0 x 1.9 metres in size. We moved from our previous house 5 years ago; it had only 6 units and 3 were misted. How does one choose a good manufacturer – what do you look for? I think drainage holes in the frame are vital.

Jade McCarthy says:
31 October 2016

I have been looking into buying some new double glazing windows for my house and came across Cherwell Windows. I went for a meeting to discuss and they have now been installed. They look absolutely fantastic and I’m very happy with the price I paid as well. If you’re looking for some double glazing windows I can easily recommend them.

Tony says:
11 June 2017

£830 for a UPVC 120×120 casement window with single opener? WHAT on earth…………….

I have just costed a project in great detail using firms in the Kenilworth/Coventry area using FENSA registered independent firms of long standing.

£425. And that was for a more expensive 2 opener (one vertical opener. 1 horizontal above it)

That’s almost half your number. Please publish the detail of how on earth you arrived at your figure.

We were planning on changing some single glazed windows but I have now now found out about LOW EMISSIVITY WINDOW FILM. This would be about 1/10 th of the cost of new windows.
Unfortunately there don’t seem to be any Which reports. Anybody tried the stuff? Info about the company, ease to fit etc would be great. Thanks

MY experience (all secondhand) with any films applied to windows, is that they get brittle and crack after a few years. Some fade too, and all require “kid glove” treatment when it comes to cleaning.

What are you trying to achieve with this film? The main benefit of double glazing is acoustic – the second skin of glass with a decent air gap attenuates sound substantially. A film won’t give you that. It could help prevent the greenhouse effect and mitigate overheating in summer – but opening the window does that. A thin film is unlikely to make dramatic difference to heat loss in the winter. What is the frame made of? A lot of heat will go through the frame not the pane.

If the single glazed window frames are in good condition, consider secondary glazing – which actually offers better thermal and acoustic performance than replacement windows, with a lot less disruption.

As supergrandie says, Which? does not seem to mention window films. Low emissivity glass, either as double-glazed panels or secondary glazing seems a much safer option. I’ve only seen films used for safety reasons and have not been impressed.

I’d forgotten that Wavechange. Back in the 70s when the IRA was busy in my home town (where Marines were based) our local pub covered the insides of his windows with self-adhesive plastic to protect occupants from implosion by external blast force. Functional – but quite a shame to have to deface the etched windows in that way.

Rather unhappy memories, Roger. Hopefully it was possible to peel off the plastic, though it might be difficult to remove traces of adhesive from etched glass.

I had a look at a couple of sites selling window films and they do seem to be removable, so supergrandie could experiment on one or two windows for little outlay.

Many adhesive films can be removed gently with a little warmth from a hair drier.

We had a limited amount of glass secondary glazing before changing all our Crittal steel windows for double glazing in double frames. I’ve no quantitative evidence to support the benefits, but the house is warmer and quieter from external noise. One problem with the secondary glazing was opening it before the windows – including the sashes and fanlight – could be themselves opened. However, it is a cheaper solution than total replacement and does not alter the look of the house (which may be important).

There is some interesting information here: https://www.buildingconservation.com/articles/secondary-glazing/secondary-glazing.htm

Our house had secondary glazing when we bought it and we lived with it the first winter. Condensation, mould and draughts meant they were replaced sharpish. Maybe they are better quality these days, but I wouldn’t want secondary glazing again.

I had never heard of this window film, and maybe it is worth having, but for some reason it didn’t appeal to me. If it is done in a factory it might be OK, but if it is applied on site, I would be very wary. I found a picture of a couple of men with what looked like a roll of cling film that conjured up images of windows covered in bubbles, creases and trapped dust.

And I might be totally off base here, but when you get what looks like many sites singing the praises of something you have never heard of, they are often all the same people pushing their product.