Those who elect to install double glazing can expect to save about one-half of their current energy consumption. Good quality double-glazed windows are extremely efficient at blocking not only heat loss but also air and noise pollution. They will make your home quieter, cleaner, warmer (or cooler in summer) and more comfortable. They're very good at their job.

One secret behind the effectiveness of a double-glazed window is the space between the two panes. This acts as an insulating barrier and, if properly sealed, will be very efficient in insulating that huge hole in your wall called a 'window'. This space may be filled with air or an inert gas (such as argon). It can also sometimes be void with a slight vacuum maintained in the space.

Some glass used in double-glazing is termed 'Low-E', which stands for low emissivity. This is a fairly new technological advancement and is extremely effective. Low-E glass has a microscopic coating on one side which is able to keep heat in your house in winter yet repel heat rays trying to enter during the hotter months of the year. This is very 'smart' glass and knows just when to keep your space warmer or cooler.

Properly installed double-glazed windows will have an air-tight seal, which is important for several reasons. One distinct advantage is the rarity of condensation forming on this type of unit. This, however, is not the case with secondary glazing, which is frequently associated with moisture and condensation problems. This method consists of putting an additional window inside your house, right over the existing single-paned unit. It's not nearly as efficient, however, it may still be your best choice.

For one thing, secondary glazing can be used even in Conservation areas and may be installed without planning consent. If your home is listed this may be your only viable option. In that case a few things should be considered.

Besides problems with secondary glazing and condensation there are also a few other considerations. Secondary, internally fitted windows may be inconvenient during the warmer months and will need to be removed and stored away. In case of an emergency (such as a fire) they might make escape from the home more difficult. But, in certain situations they are definitely a viable option.