Reducing Energy Costs With Double Glazing

A significant source of heat loss which should be considered is single glazed windows, and this amounts to round about 20 per cent, according to the area of glass.

Although glass is a poor conductor of heat, a window pane is so thin that warmth escapes through it at two or three times the rate of a wall. In older types of houses this does not add up to so much in toto because areas of glass are small in proportion to other building areas. With modern large picture windows, however, heat loss is considerable.

You can add an extra pane, and, though it is impossible to fill the cavity thus formed with insulating material without obscuring vision, you can at least entrap a column of still air. Double glazing, as it is called, helps to reduce traffic noise and cuts condensation to a minimum.double-glazing-heat-loss-reduction

Double glazing acts rather like a woollen garment but, instead of trapping still air in a number of tiny pockets, it performs the same function in one volume, between two sheets of glass. This enables a room to rise 5 to 6 per cent in temperature without additional heating, and so should come before the installation of central heating because it will make the most of whatever existing source of warmth you have. Installing two panes of glass where there was only one before makes every inch of room space available for sitting in, even close up to a window, without your feeling cold.

Panes 20 mm (1 in) apart insulate quite well and at the same time slightly lessen traffic noise. When 100 to 200 mm apart (4 to 8 in) they are extremely efficient and reduce even the loudest outside sounds to a distant murmur. And when the panes are hermetically sealed by the manufacturer they are even better.

The installation of factory-sealed units entails taking out thold frame and is best carried out under the manufacturer’s guidance. Most of them have accredited operatives spread around the country.

You can easily put unsealed units in yourself. Mostly they take advantage of the existing pane. You have only the other pane to add, so saving money.

The expression ‘unsealed’ has been used, but really they are sealed to a certain extent — in so far as the fitting is very tight indeed. The snag is that during hot weather entrapped air expands and bubbles out — rather like a slow puncture in a motor car tyre. And when the weather becomes cooler the entrapped air will contract and suck in outside air by a reverse process.

So, however dry the atmosphere is when you install the fitting, the space between the panes eventually will become damp and mould will form. You can minimize the trouble by inserting a small bag of silica gel crystals, obtainable at chemists’ and do it yourself shops, in a corner of the space where it can be hidden by a curtain.

These unsealed units can be opened up for cleaning. Some are side- or top-hinged, some are sliding, some lift out and some can be unhinged and lifted out. Hermetically sealed units cannot; but then they do not need interspace cleaning.

In addition to the silica gel crystals you can bore 2, 3 or 4 mm holes sloping down towards the outside, through the bottom rail, to carry off whatever water may collect. Most of these units are extremely efficient.

Awkward-shaped windows

Don’t jump to the conclusion that because you may have an awkward-shaped window it cannot be double glazed. The ingenuity of manufacturers is amazing in this respect. If the frames are of metal instead of wood they can be drilled and tapped, extra large picture windows can be accommodated with more than one unit, bay windows are dealt with independently, and windows with extremely narrow surrounds can be stepped.

A sliding sash window is accommodated with a second pane fastened on to the reveals to cover the entire opening, or a unit is added inside the bottom sash and outside the top sash, so allowing the window to open. In this case, compensation for the additional weight of the fittings will have to be made, otherwise the top sash will never remain closed and the bottom sash will open of its own accord.

Compensation can be provided by adding short pieces of lead piping over the sash cords or buying new weights of the correct size. Sash weights are concealed behind the pulley stiles at each side and can be reached by prising out a small slab of wood located near the bottom of each pulley stile.

If you wish to mark glass as an aide memoire when installing you can write on it ‘Top’, ‘Bottom’, ‘This side out’, with a chinagraph pencil or write on sticky tape with a Biro pen.

Room extensions can be fitted with patio double-glazed doors which, when on the wide side, could allow a considerable amount of heat to escape if they are not so glazed.


Double glazing a whole house in one go will run into hundreds of pounds. It will be less when installed during the building of a new house.

If funds do not permit a complete job in an old house, carry out the work piecemeal, dealing with the most used or coldest room during the first year. The following year, see to another room — and so on.

The slight extra cost of adopting this policy will be more than counterbalanced by your not having to pay interest on a loan. Another advantage is that you will have the opportunity of learning as you go and trying the products of different manufacturers for different rooms.