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1. Using a rubber mallet and a strong pallet knife, remove the beading around the window. You might think they’re part of the frame, but they’re actually separate on the inside of the frame and can be taken out by using pallet knife to prize them out. Start with one of the longest beads first and leave the top bead until last.
2. Give the glass a little tap to loosen it if it doesn’t come out straight away, then the whole unit should slide out easily. Just make sure it falls towards you and not back out onto the ground below!
3. Clear any debris that has found its way into the frame with a brush. Add spacers at the bottom of the frame – these could be pieces of plastic.
4. Get your new sealed unit (make sure you measure the glass before you buy one so you know which size to get) and carefully take it out of the packaging. Look for the British Standard mark – that shows you the bottom of the glass.
5. Lift the glass into the frame, starting with the bottom first, and make sure that it fits square in the frame before taking the spacers out.
6. Use a little washing up liquid to spread along the beads to make it easier when you slide them back into the frame. If they simply push and clip back in, you can use something like a block of wood to help you push them in correctly. Put them back in reverse order to how you took them out.

As well as keeping your home warmer and reducing noise, you’ll notice a saving on your energy bills from installing double glazing. If you install A++ rated windows in your home after having single glazing, you could save up to £120 year on your energy bills. The Energy Saving Trust has more information.

• Climate - If your window faces south, it will be subject to direct sunlight for a lot of the day. This tends to cause the sealed unit to fail more quickly – a south-facing window may last between 10-25 years. This is because the spacer bars will twist as the temperature rises and causes the adhesive holding them together to eventually fail.
• Moisture - Windows in kitchens and bathrooms tend to fail more quickly because they come into contact with moisture more often. For example, if water gets on your windowsill when you shower, the seal around the glass will come loose more quickly if it’s constantly wet.

You can only repair blown double glazed windows in the sense that you can replace the sealed unit (the glass part of the window) instead of having to replace the entire window.

When a double glazed window is blown, it means that the seal around the window has failed and is now letting air in and out. Often the first sign that the sealed unit has blown is condensation on the inside of the window, which is annoying since there’s no way to get rid of it! When your sealed unit has blown, you’ll be losing heat out of the window, meaning you could be spending more on your energy bills.

As a temporary fix, you could see if you can buy a misting repair kit online, but the condensation will eventually occur again as the air gets in. The best thing to do is ask a window installer or glazier to replace the sealed unit for you.

It's simple to replace the glass in a window – the specialist will remove the beading around the window, remove the blown glass from your window frame and set it to one side. They will then clean up around the frame before adding spacers in, then fitting the new sealed unit into the frame. They’ll make sure it’s a snug fit before replacing the beading back around the window to secure it.

There's no reason to put off repairing a blown double glazed window since the cost is generally much less than replacing the entire thing. A sealed unit with installation costs an average of £100, whereas a completely new window will cost around £400. You’ll soon notice that it’s less draughty and will be able see out of your window once you’ve had the blown glass replaced.

Whether you need toughened glass in your windows depends on where the windows are in your home or business. Toughened glass is sometimes referred to as tempered or safety glass, and it just means it’s stronger than the standard glass that’s usually offered with double glazed windows. So how do you know if you need it?

Toughened glass is useful in areas of your home where you might come into contact with the windows if you were to trip and fall. If you put your hands out to steady yourself on standard glass the chances are it would break into large sharp pieces with jagged edges. Of course, this means that you could seriously cut yourself if this were to happen. With toughened glass, the structure of the glass is changed so that if it breaks it shatters into lots of tiny pieces, minimising the risk to you if you were to fall on it.

You might want to use toughened glass in patio doors, low windows or frames next to doors. It just means that you will be safer if the unlikely happens and you or a family member falls through the glass. There are certain requirements through Building Regulations with windows at a certain level, but any reputable window installer should be able to go through these with you if you need to replace your windows with toughened glass. The regulations will only apply to new windows – there's no need to switch your windows to toughened glass early, but when you do come to replace them you’ll need to make sure they meet the standard.

The energy efficiency of windows is measured using ratings, varying from A, the most efficient, to G, the least efficient. This scheme is run by the British Fenestration Council (BFRC). To comply with Building Regulations you’ll need windows of energy efficiency at least level C.

Double glazing frames don’t just have to come in uPVC and are available in other materials including aluminium and wood too. Wooden or timber windows are more suited to properties with a traditional look and are often the frame of choice for listed buildings and homes in conservation areas. When properly maintained wooden windows can last well for years but can be up to three times more expensive than uPVC.Aluminium is the strongest and most durable option. As a metal it is highly resistant to the UK’s changing weather conditions and won’t rust, warp, crack or peel. Aluminium offers a modern appeal and is available in a range of colours.

By replacing the single glazed windows in your home you stand to make savings of around £170 each year. It’s not just the financial gain that makes double glazing attractive though and you can also save up to 680kg of carbon emissions annually. Over 20 years this is a saving of around £3,400 and 13,600kg of CO2.