We've asked thousands of double glazing customers to rate the company they used, including brands Anglian, Everest and Safestyle, as well as independent traders.
The answers, from more than 3,000 double glazing customers who bought double glazing in the past 10 years, mean we've rated more double glazing brands than ever before. The results reveal big differences between brands.
Nearly 30 percentage points separate the top and bottom overall scores. Some glazing firms achieved a full five stars for customer service, while one company gained just two stars from customers for value for money and after-sales support.
Our results rate each double glazing company across lots of factors, including customer service, quality of products and installation, knowledge and helpfulness of staff, and how much mess they made during the installation.
Below, we reveal how double glazing companies fared on everything from customer service to value for money - according to their customers.
Only Which? members can access the customer ratings in the table below. If you're not yet a member, to unlock our results and see analysis on which areas the companies are succeeding in, and how they're failing their customers. This will also give you access to the full reviews of , , and more.
Big differences exist between the highest and lowest ratings and customer scores achieved by companies in our survey. On customer service, one brand only gained three stars, based on its customers' feedback, while others achieved five stars.
The table gives a snapshot of the areas on which we've rated double glazing firms, based on the feedback of their customers. Our full ratings cover sales and purchase, delivery, installation, after-sales support and how well the windows or doors stand up to the test of time.
Double glazing companies rated by their customers
Double glazing firm
Knowledge of salesperson
Quality of products
Value for money
Our ratings include customer feedback across all aspects of buying and owing double glazing – from sales and purchase, to delivery, installation and how well the windows or doors lasted.
The results for each company are based on our survey of 3,467 people in August 2020 who bought double glazing for their home in the last 10 years.
Customer scores are based on a combination of how satisfied customers of the brand say they are, and how likely they are to recommend it, if asked.
We also ask customers to rate more than 10 other aspects including the choice of products, clarity of documents (e.g. the contract), how well the installers communicated and how well the double glazed windows or doors have lasted. Customers rate them on a scale from very poor to excellent which we translate into a star rating.
Besides rating eight of the biggest double glazing brands, we have created a dedicated advice guide for buying from an as 45% of people in our survey bought from a local or independent double glazier.
The three biggest double glazing chains have been included in our annual survey for several years. This year, one of them scored lowest out of the eight firms in our survey and was the only firm to get two out of five stars on some aspects of its service.
Britelite is included in our double glazing survey for the first time this year. It has more than 45 years' experience of fitting windows, doors and conservatories.
The firm says it has always aimed to supply the best product at the keenest price and serves customers in Kent, Sussex, Essex, Surrey and London.
Britelite installs windows, doors and conservatories in Kent, Sussex, Essex, Surrey and London.
All of its products have a 10-year guarantee.
Coral Windows was included in our double glazing survey for the first time. It says it prides itself on quality and excellent customer service. But how did it fare in our survey?
Serving households in Yorkshire since 1990, Coral Windows has three showrooms and develops, designs and manufactures all of its doors, windows and conservatories in Bradford.
Unusually, it doesn't take deposits; customers pay in full when their project is complete.
Its uPVC frames have a 15-year guarantee, and sealed units have a 10-year guarantee.
CR Smith says that customers will feel good about their choice for years to come. Which? members can to find out what customers thought of the brand in our survey. If you’re not a member, you can to see our exclusive ratings.
This is the first time that CR Smith has had a rating in our double glazing survey, but how did it get on?
The Dunfermline-based firm has been fitting double glazing for more than 40 years, although the name has been around for over 100 years. It has its own manufacturing plant and employs more than 400 people.
CR Smith sells a range of double-glazed windows, including sliding sash, casement, tilt-and-turn and reversible styles. It also offers a range of front doors and patio doors, , orangeries and sunrooms, and will both build and decorate them.
All its Lorimer windows have 10-year guarantees for parts and workmanship. It also promises to replace any window or door fitted in brick surrounds if it fails when an intruder breaks in (unless they break the glass).
It has a 24-hour, 365-day emergency call-out service to help if you have an urgent problem, such as a security risk, or you’re locked out.
Crystal Windows and Doors was rated in our double glazing survey for the first time this year. So how did it compare with other big brands?
Based in Essex, it installs a range of windows and doors for homes and garages and also does roofline work, including soffits and fascias.
Crystal Windows and Doors has been trading since 1995 and makes all of its products in its Romford factory. It says that it’s focused on continuous improvement to products and services.
It's not the same company as Crystal Direct, a Hertfordshire manufacturer of PVC-U windows, doors and conservatories which are available in B&Q and Screwfix.
Crystal Windows and Doors sells a range of double-glazed windows, including sliding sash, casement, tilt and turn and reversible styles. It also offers a range of front doors and patio doors, as well as garage doors, roof services, driveways and spray-foam insulation.
It offers a 10-year guarantee, which it says is its customers’ favourite feature. It says that this means if you have any problems with its products, its dedicated team will help sort things out.
First Home Improvements says it offers a first-class service to help customers choose the best double glazing. Which? members can to find out if First Home Improvements lives up to its promise, according to customers in our survey. If you’re not a member, you can to see our exclusive ratings.
First Home Improvements claims to be one of the longest-established double glazing companies but this is the first time it has been included in our double glazing customer survey. Find out how it fared.
It supplies double glazing to homes in the east of England, from Sussex to Lincolnshire, and makes its products in Norwich.
It offers a 10-year warranty on all products, and 12 years on windows.
A large proportion of the double glazing owners we spoke to (45%) used an independent company. This includes double glazing firms local to them and independent companies not in their area.
It may also include local builders and joiners, who you're more likely to use if you're having new windows or doors as part of a home renovation, such as a new extension.
All traders who use our logo have been through rigorous background checks, done by ex-Trading Standards assessors. The traders must also agree to follow our code of conduct and are checked on an ongoing basis.
No matter how good a company is, problems can arise. To help you avoid potential pitfalls, we asked double glazing customers what issues they came across with the purchase, delivery and installation of their double glazing.
Reassuringly, 73% of our survey respondents said they had no problems.
Post-installation problems were the most commonly reported, followed by installation problems, delivery problems and problems when buying.
While 18% told us about post-installation issues, just 2% reported a problem with buying their double glazing.
The most common post-installation problems include doors and windows becoming difficult to open or close, and windows or doors sagging so that they don't fit as well.
To head off potential problems early, make sure you have a clear idea of what you want, that you understand what you're buying, you get clear and detailed information and that you don't feel under pressure to make a purchase quickly.