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All new windows come with an energy efficiency rating from A to G. A is best, while G is the lowest rating. Anything above C is considered good, but these days most companies will be able to supply you with A-rated windows to maximise your energy efficiency.

Are you about to purchase a double glazed unit and wondering how to go about the replacement project? If yes, then you’re at the right place. Firstly, it’s advisable to hire the services of a reliable professional who can guarantee the best results for help especially if you lack proper training and experience in the field. However, we’ve put together this step by step guide to provide you with a detailed information about the double glazed unit replacement process. Let’s get started!

The tools and materials you require for the project includes tape measure, hammers, nail punch, scraper, spacing blocks, non-hardening butyl putty, high-security glazing tape rolls and beading tacks.

• Work out the glass size required. Simply use the tape measure to measure from frame edge to frame edge while also taking note of the thickness.

• When about to order, inform the glass merchant that the measurement provided are frame-tight. This will make him reduce the dimension a little bit, mostly by 5mm for clearance.

• Remove the beading and ensure to support the glass while doing so. If the glass units are fitted in wooden windows, you may need to cut the putty-based compound they’re normally sealed with to remove the glass.

• Lay out the beading in the window’s shape to make for easier refitting later on.

• If you’re working on wooden frames, wipe out all traces of excess installation compound using a scraper and clean the rebate with a soft brush.

• Trial fit the double glazed windows to ensure they’d slide into the frame without being forced.

• Plastic frame windows are usually in between a pair of gaskets, you should replace this with a hight security glazing tape. While for a wooden frame, simply apply strips of flexible non-setting butyl putty or high-security glazing tape on either sides of the glass.

• Install and centralize the glass in the frame.

• Press the nail wooden beading or plastic beading back into place.

Yes, of course! It’s common for people to replace just one double glazed window. One reason that people want to replace one window is that the sealed unit inside has failed. You’ll know if this has happened because you’ll be able to see condensation on the inside of glass, which gets frustrating because you can’t wipe it away. In this case, you can choose to simply replace the sealed unit or the entire frame, which you might want to do if it’s looking past its best.

When you’re replacing just one double glazed window, if you know the brand of your current windows you could ask your installer if they can source the same ones. This will help to keep them looking as similar as possible, although if your existing windows are very old you may notice some discolouration on the exterior compared to the new one, and locks and trickle vents might look different.

Replacing just one double glazed window shouldn’t take a qualified window fitter long, and could cost as little as £400. If you want to simply replace the sealed unit, that may only cost around £250. You could try to fit a new window yourself, but it’s worth bearing in mind that all replacement windows need to be certified that they’ve been installed to meet building regulations, so you’ll need to apply to your local building control officer who will come and inspect the work then issue a certificate. If you ask an installer who is registered with a self-certification scheme (like FENSA) to fit the window for you, they can issue the certificate themselves when they’ve finished the work.

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.

• Impact from a stone or other object smashing the glass in a ‘bullseye’ effect
• The result of a break-in
• Extreme weather or changes in pressure causing a crack
• The sealed unit being ‘blown’, meaning that it’s no longer energy efficient due to air leaking out

Ultimately the double glazing company you use is responsible for the quality of work and to ensure your windows are of an excellent standard. This is why it’s important to get a warranty and use a Fensa registered installer. If problems emerge within a couple of years then it’s likely the installation was of a poor standard.Contact the double glazing company and have the issue repaired or new windows replaced. This doesn’t matter if you received a discount of free windows as part of the deal. As long as you entered into a contract the company is obliged to restore the windows.

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.

Accidents happen, and sometimes windows get broken. And that will lead to you wanting to replace just the glass in your window, rather than the whole frame. Also, as windows get older they can mist up on the inside, which means that the unit has ‘blown’ - so you’ll also need to replace the glass. But how much is it to replace the glass in a window? Luckily, if the frame of your window is in good condition, there’s no need to replace it, and this will reduce the cost. For an installer to fit a new pane of glass in a single glazed window, the average cost is £100, while a replacement double glazed sealed unit will cost an average of £110. Of course, as this is an average, if your window is very large you may spend more, and if your window is very small the price may be less. That's why it’s important to get a range of quotes so you can compare costs and get the best price. If you’re good at DIY, you may feel confident enough to have a go at replacing the glass in your window yourself. In that case, the cost of sealed unit and any other materials you need will cost an average of £57. It’s a significant saving, and if you think you can do it, then give it a try. However, if you’re in any way unsure, it’s best to leave it to the professionals. A window installer will be able to replace the glass in your window in less than an hour. Even though it costs more for a professional to do it, if you get it wrong and have to start over it will cost you more in the long run.