How to make your Windows more Energy Efficient

A little advice on how to make your windows more energy efficient in both the short and long-term.


Around 20% of all heat lost from a home is accounted for by windows and doors, according to National Insulation Association figures. A draughty single glazed window will also have a big impact on comfort due to cold air seeping into the home, but this and your energy bills could be helped by making your windows more energy efficient.

Heat loss from windows is a little more complex than you might think. There are two factors which have the greatest impact upon how well or how poorly a window conserves heat:

1. The U-values of the glazing and the frame;

2. The airtightness of the window as a whole.

The latter can be especially problematic with old sash windows, which are surrounded by more gaps for draughts to creep in through. English Heritage undertook research with found that 60% of heat loss could be down to air leakage through windows and doors.

What should you do to make windows more energy efficient?

You will need to focus on two main objectives, which are:

1.  To improve the insulation values of the window, and;

2. To reduce any uncontrolled air movement.

There are numerous options when it comes to achieving these goals, but the decision you make will ultimately come down to whether or not you refurbish or replace your windows.

Improving Airtightness

One way to makes windows more energy efficient is to improve air tightness. Draught proofing can make a difference straight away and it won’t cost much, either. You can give this a go yourself, but it is best to get an experienced joiner in to do the job properly. There is a significant difference between well-installed, wooden draught proofing systems and DIY sticky-backed rubber strips.

An old wooden window which might seem beyond repair can in fact be made to look and act as new. Air leakage can be reduced and will often be achieved at the same time as draught proofing. It will be essential to regularly maintain timber windows in order for them to work as best they can, and a well-looked-after wooden window should last longer than the person who made it. uPVC windows, on the other hand, can need to be replaced after only 20 years.

Improving Insulation Values

An increasingly popular method used to make windows more energy efficient is to keep the box and sashes of the windows and to install new double glazing. This is possible in many cases, but many windows made in the early 20th century or earlier were simply not designed to hold the weight of a double glazed panel.

Fitting secondary glazing will improve the window’s U-value, although not as much as modern double glazing. Where noise is an issue, secondary glazing fitted with a large air gap is often a better solution to the problem. This method is also much cheaper than the alternative of fitting new windows and when it comes to listed buildings and conservation areas this may well be the only available option. It is also important to consider ventilation.

The best way to improve your windows’ U-values is to upgrade the glazing to either modern double or triple glazing. The typical U-values for single, double, and triple-glazed windows are 5.0W/m2, 1.7W/m2, and 0.8W/m2 respectively. Improving your glazing also has the added benefit of improving comfort as the window is likely to retain more heat.

These figures have quite an effect on the temperature within a room. In a case where the outside temperature is -5°C and the indoor temperature is 21°C, the temperature beside a single glazed window would be 1°C, whilst beside an older double-glazed window it would be 11°C, rising to 16°C with newer double-glazing, and reaching 18°C beside a triple-glazed window.

So, what should you do?

It is possible to significantly improve airtightness without replacing any windows, but if you truly want to make a difference and combat heat loss through glazing then new windows is probably the best option you have. Of course, you can always begin by using curtains, shutters, and blinds whilst you save up the funds to carry out the heavier work.

However, be aware that there is little point in fitting the best triple-glazed windows if your home is otherwise of a low thermal standard. Also, if your windows are in good shape, try upgrading them rather than replacing what could last for years longer.

There is no clear answer to what you ought to do to make your windows more energy efficient, and you will find that there are various things to consider when you choose to do so. Be sure to bear in mind all of the available options, and make sure that you opt for a supplier whom you are able to trust. Making the decision is the easy part, and the practical problems can all too easily come around later on.

Image by RedCoat

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