How important are windows for retaining heat in the home?

I am sure most of you have had a double glazing salesman tell you how important windows are for keeping heat in the home and helping to save you money on your heating bill.

Just how important are double glazing windows though? And when you compare them to other energy efficiency improvements – which are better in terms of payback time on the initial investment?

Let’s start by looking at some of the more common energy efficiency upgrades for the home and their relative cost. Putting modern energy efficient double glazing in a home with single glazing will save you around £100 a year on a semi detached property (around £50 for a flat and £150 or more for a detached house). In comparison, cavity wall insulation and loft insulation could save you upwards of £150, and at a much lower cost.

Let’s have a look at the payback time:

Measure Typical Cost Typical Savings (per year) Typical Payback Time
Double Glazing £10,000 £100 100 years
Cavity Wall Insulation £1,000 £150 7 years
Loft Insulation £300 £150 2 years

As we can see, the payback on glazing compared to other measures is very poor.

Why is glazing so poor at paying back?

There are two main reasons why the payback for glazing is so bad – the first is the cost of a window (glass + frame materials) compared to something like fibreglass insulation. When you consider the windows need to be made to measure, as well as the fact they have mechanical parts (sash windows or hinges) and some include vacuums between the glass it is obvious that the cost is far more expensive than a roll of fibreglass for your loft.

The other reason glazing doesn’t pay back well is that the area of window compared to the area of exposed wall is so little. A typical house may only have 10-15% of its surface area as window – compared to the remaining 85-90% as cavity wall. So improving the insulating properties of that wall is a far better investment than installing brand new windows.

It is also important to note that you can make big gains on the efficiency of your windows by simply adding some good draught proofing or inexpensive magnetic secondary glazing. New windows are nice to have, but there other energy efficiency measures that we would get installed first based on the payback. Having said that, windows do definitely improve the comfort of the property, and if the seal has gone in your old double-glazing and they have fogged up – replacing them might be the only option.

Funding for windows

The other thing that makes windows less attractive as a measure is that the funding available is not particularly great. You can get up to £650 cashback on the Green Deal, and perhaps get 10-20% financed (paid back on your electricity bills via the Green Deal). Compared to solid wall insulation, for example, which pays up to 75% of the cost in the form of a grant, it doesn’t sound too attractive.

Replacing old double glazing

Everything we have talked about up until now assumes you have single glazing at the moment. Of course, if you already have old double glazing that you are thinking about replacing – it will still be better than single. So that means the savings to be made by switching to new double or triple glazing from older double glazing are even smaller. In some cases you are looking at just a few pounds a year!

Old Windows

Old windows with rotting frames may need to be replaced anyway.

That means it is never usually worthwhile getting new windows on energy efficiency grounds alone. If you have other reasons for getting new windows – like reducing noise, rotting frames or aesthetic reasons, then of course it may make sense for you. Just remember that there are a whole host of other measures that will save you more money at a lower cost!

Think we missed something? Do you have a different opinion?

Comment below to get your voice heard…