Most window installers will be able to provide you with one double glazed window and fit it for you. If you’re replacing one double glazed window in your home, ask them to try and source the same windows that you already have or find one that’s very similar. Externally, you probably won’t be able to notice the difference, but if your existing windows are very old there may be some exterior discolouration and the locks and handles might look slightly different.
If you want one double glazed window so you can fit it yourself, there are lots of online companies that can supply you with one window. However, window fitting is a skilled trade and you might want to consider whether you have the right tools and experience to fit it yourself. Of course, you’ll save money on installation costs, but if something goes wrong, you might end up shelling out to get it fixed anyway.
The other thing to consider is that any replacement windows need to be certified that they meet Building Regulations. If you fit the double glazed window yourself, you’ll need to apply to your local council building control officer to get a certificate that confirms that you fitted the window within the regulations. You’ll have to pay a fee for this, and it will be even more expensive if Building Control say that the window hasn’t been fitted within the regulations and you have to start again.
The alternative is to ask a reputable window installer that is registered with a self-certification scheme, like FENSA, to install the window. That means that they can self-certify that the window meets building regulations once they’ve finished the installation.