Window Energy Saving Calculator

Let's Work Out Your Potential Savings

Window Energy Saving Calculator

08 June 2018

How To Calculate How Much Energy Your New Replacement Windows Will Save You

It’s a well-known fact that replacing your old windows with high-quality windows that have double or triple glazing will reduce your energy consumption. But just how much should you save from your replacement window investment?

Signature has put together a simple Window Energy Saving Calculator that you can download to see the real difference your new quality replacement energy-efficient windows can make.

Why U-Values Are Important

U-Values are assigned to building materials to indicate their thermal resistance (i.e energy-efficiency). The U-Value tells you how quick or slow it takes for heat to transfer through the building material.

A window’s total U-Value is made of the frame, glass and spacer bars. It’s important that the total Window U-Value (e.g Uw-Value) is represented properly and not just the glass (Ug-Value) as this is a more accurate depiction of the energy performance.

It also vital to be wary that this is an uninstalled energy value which is why you should opt for quality certified installers. A windows U-Value is only as good as the final installation.

Should You Just Look At The U-Values Of The Window?

It’s easy to get lost in the window jargon that can easily arise when trying to work out simple questions like “how much should my new energy efficient windows save me?”. Yes, U-Values are important to look at, but you also need to consider both the air-tightness and water-tightness of your windows.

The air-tightness indicates how likely air will leak through your windows and gives you an idea of the overall build quality. The water tightness will tell you how likely water is to penetrate your windows. Learn more about window performance ratings here.

Energy Window Savings Sample

Now to 100% accurately work out the exact savings that you can make with energy-efficient windows would require a wide range of variables to take into account. However, Signature has put together a formula that will give you a rough estimate of what you should expect with your new windows. We’ve also included a Window Energy Saving Calculator at the end of this blog so you too can work out your potential savings.

So let’s say you’re replacing 40m2 worth of windows. One company is offering double glazed windows with a Uw-value of 1.4 W/m2k while another is offering triple glazing with a Uw-Value of 0.8 W/m2k. We’ll also assume that you heat your home for only six months of the year.

To calculate your potential savings we’ll need to:

  1. Work out the U-Value Difference (1.4 – 0.8 = 0.6 Uw-Value difference)
  2. Work out the total window glazing u-value area in your home (40m2 x 0.6 U-Values Difference = 24 U-Value area)
  3. Find the average temperature difference inside/outside your home (21C Inside – 4C Outside = 17C difference)
  4. Multiply the U-Value area against the temperature difference (24 U-Value Area x 17 Temperature Difference = 408)
  5. Convert this figure to Kilowatts per hour (408 x 1000 = 0.408)
  6. Convert this figure to Kilowatts per annum (0.408 x 365 = 148.92)
  7. Multiply by the cost of a kWh of Gas/Oil (148.92 X €5.83 = €867.46 annual savings)

So why’ll this is only a rough estimate, you can see that the potential savings can be huge when it comes to choosing your energy-efficient windows. With 40m2 high-quality triple glazed windows (0.8 U-Value) you could save up to roughly €867.46 when compared to standard double glazed (1.4 U-Value) :

  • €867.46 in 1 year
  • €8,674.59 in 10 years
  • €17,349.18 in 20 years

Signature’s Near-Passive Standard Aluminium Clad Wood Windows can reach U-Values as low as 0.65 W/m2k. Learn more about our Next-Generation Energy-Efficient windows here.

Work Out Your Potential Savings Using Our Window Energy Saving Calculator

Signature has put together a quick window energy saving calculator so you can work out the savings you could make with triple glazing. Just put in the U-Values of the two different window types, the total size of glazing area and the current cost of a kwh of gas/oil. The calculator will do the rest of the calculations for you.

Download Window Energy Saving Calculator

Start your download by clicking on the link below and carefully follow the instructions.


If you're interested in finding out more about us, information on our latest shows or to book a showroom appointment please fill out the form below and your download will begin afterwards.

Alternatively click here to download the file

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