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How to buy double glazing

Double glazing explained

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Double glazing explained

We explain the advantages of double glazing, how much you could save on your energy bills and what types of double glazing are available.

We explain how double glazing works, how much you could save on your energy bills, the different types of double glazing frames, and what the energy ratings mean.

For many households, having double glazing installed is a key way to reduce your energy bills. In fact, 44% of people we surveyed* who have double glazing said that they bought it to make their home warmer, and 40% to reduce their energy bills.

If you decide to go ahead and buy double glazing, we can help you choose the best double glazing company for your home. We surveyed thousands of double glazing customers to reveal what they really think about their double glazing firm. To find out more, see our double glazing company reviews.

*In August 2016, we asked 2,239 Which? members about their experiences with buying double glazing, as well as the company they bought double glazed windows and/or doors from, and had them installed by, in the last five years.

What is double glazing, and what are the advantages over single glazing?

Double-glazed windows consist of two panes of glass separated by a layer of air. Double glazing has many benefits over single glazing (where there's just one pane of glass and no air layer):

  • Keeps warm air in, meaning your property is better insulated. This results in fewer draughts and cheaper heating bills.
  • Keeps noise out - you'll hear far less noise from outside with double glazing.
  • Reduces the amount of condensation on the inside of your windows.
  • Heightens security - double glazed glass is more difficult to break than single glazing.

How much cheaper will my energy bills be if I install double glazing?

Some 60% of homeowners said that their home was warmer since getting double glazing, which is one of the biggest differences people cited that it had made. However, only 36% said that they thought it had actually reduced their energy bills.  

If you were to replace all of the single-glazed windows in a three-bedroom, semi-detached house, the Energy Saving Trust says that you'd save between £75 and £100 per year with B-rated glass and £85-£110 per year with A-rated glass.

As double glazing should last for at least 20 years, that's a saving of between £1,500 and £2,200 over 20 years. 

The picture below is a thermal image showing the difference in heat loss between single-glazed and double-glazed windows. The house on the left has a single-glazed window where we can see more heat escaping - indicated by the bright-yellow colours.

What types of double glazing frames are there?

The most common type of window frame for double-glazed windows is uPVC - or, to give it its full name, unplasticized polyvinyl chloride. Not only is it up to three times cheaper than traditional wooden frames, but it's also recyclable, durable and the most energy-efficient frame type.

uPVC window and door frames are available in a variety of colours and finishes, including wood, but white is the most popular option. uPVC is easy to keep clean, too, requiring little more than a wipe down with a soft cloth and a spot of washing-up liquid every now and again.

Alternative options to uPVC include wood or aluminium frames. Timber is a greener option than uPVC as it's a naturally renewable material. Many people feel wooden windows look nicer and more subtle than uPVC, particularly in traditional or period-style properties.

While timber windows tend to be more expensive and need maintenance, if properly looked after, they can last a very long time.

Before you speak to any double glazing firms about double glazing, make sure you know how much it's going to cost so you don't get overcharged. We have typical costs for different types of windows and doors - see double glazing prices.

What is the Window Energy Rating (WER) system?

The Window Energy Rating system (pictured above) follows a similar pattern to appliance energy labels, with windows being rated between A+ (the best) and G (the worst). Building regulations require all new windows to be at least C-rated.

Each of the big-name companies claim different levels of energy efficiency, some as much as A++. 

We calculated that getting B-rated windows instead of C, or A-rated instead of B, would save around an additional 6.5% on your energy bills. And the cost of going up a rating is up to 15% extra per window, so it's worth looking at how much it will add to your quote before choosing. 

Are there any alternatives to double glazing?

If you're unable to install double glazing (for example, if you live in a listed building), secondary glazing is an alternative. This involves fitting a second layer of glass inside your existing windows. It isn’t as effective as full double glazing, but it could still save you some money on your heating bills - and it's much cheaper to fit.

Now you know more about double glazing, find out which firm you should use. Our survey of double glazing customers reveals how well-known firms Anglian, Everest and Safestyle compare with each other and local independents. See our double glazing company reviews.

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