While most buyers of double glazing are looking for replacement windows to help reduce their energy costs, or because their old windows are rattling in their frames, there's a whole class of buyers who are 'trading up' - replacing perfectly good window frames for the sake of having the windows they want. They may be looking to replace all of their windows with a different style, or trying to restore their home to its architectural period.

And then there are the homes that were fitted with the first wave of double glazed windows in the 1960s and 1970s. The original windows that featured double glazing as an energy saving measure were aluminum framed and conformed to the best energy standards of their day. There have been enormous advances since then - in materials, techniques and styles. For many people, it's time to upgrade to the new standards, even if the old windows are still holding firm.

There are other reasons that people turn to replacement windows as well. Last spring, for instance, my mother decided it was time to replace the mullioned casement windows in her kitchen. She's always hated them, but they came with the house - and were brand new when she bought it. She shopped around for months until she finally found exactly what she wanted - a full three three-sided greenhouse window with shelving built into the window frames. Each pane is double glazed, and the entire effect is stunning. Her choice of replacement window transformed the entire kitchen.

Whatever your reason for seeking replacement windows, the following advice can help you choose the right ones.

Prioritize your needs

Think through your reasons for replacing your windows and place a priority on each. There are many choices of materials and styles of replacement windows available, and each has distinct advantages over the others. If you're concerned with restoration, for example, and want authenticity, then wood framed double glazed windows will probably be at the top of your list. If your primary need in replacing windows is affordability, then PVCu framed windows are a far better choice.

Do your research

Research windows and styles, certainly, but also check into the companies that you choose to do business with. Ask around to friends who've replaced windows about their experience with particular suppliers and contractors.

Invite three to four companies to your home to get an estimate

Don't make a choice based on one

Always have your windows measured by a professional

Don't order based on your own measurements, no matter how reliable you think they are. Choose a company that will take the measurements themselves, if for no other reason that it then becomes THEIR responsibility if any of the windows ordered don't fit the space for them.

Finally, don't assume that you're stuck with the same look you've got. Replacement windows can make a spectacular difference in your home's appearance and value. Barring prohibition for historical or council reasons, you can have that picture or bay window you've always wanted. It's all a matter of finding it.