Did you know that up to 20% of your home’s heat can be lost through your windows? Coming into the colder months, you may start noticing the draughts, cold spots and condensation appearing throughout your home.
As much as it is a big investment, now is the perfect time to think about replacing your old windows. However, they are a long-term purchase, so it’s important to get it right!
Looking round, you will see everything from BFRC ratings to U-Values, WER ratings to simply ‘our windows are energy efficient’ but what do they all mean? And how do you know that what you’re buying is really going to keep you warm this winter and reduce those energy bills?
Well, here’s the science…
A window features 2 components, which are key to energy efficiency
- PVCu frames
Let’s start with the PVCu frame
SolarFrame’s innovative window frames aren’t completely hollow as you may think, they feature multiple “chambers”.
These chambers prevent the cold outside from being transferred into warm homes because they break up mini convection currents and lock in pockets of air.
But what does that mean?
This essentially means the cold air will be at its coldest point on the outside, and gradually remains a consistent but slightly warmer temperate throughout the profile. This keeps your well-earned warm air, on the inside and staying in your home.
The glazing also plays a huge part in keeping you warm and toasty throughout the winter months. Double glazing (or triple) refers to the number of layers of glass that are used in the window. If you look at the glazing units in modern windows, you will see a strip of material in between the panes.
This material not only spaces the glazed panels, but also helps prevent the transfer of heat. The space created between the panes of glazing, is then filled with gas, usually either air, argon or krypton – which again adds to the energy efficiency.
Can you know how energy efficient a window is just by looking at it?
You can’t! But there are many tests our windows go through and then are given ratings.
You may have seen what is called a ‘U-value’. The lower this is, the more energy efficient a window is. A U-value is the measure of the heat loss in watts (W) per square metre (m²) of material when the temperature in kelvins (K) outside is at least 1 degree cooler. You will see it written as W/m²K!
Old double-glazed windows, have an average U-value of between 2.8 and 3.0W/m²K, modern PVCu windows as low as 0.8W/m²K – quite a difference!
There is also what is known as a G-value. This evaluates how well your windows capture the heat. For example, a window with no glazing would have a G-Value of 1, which would mean it gains 100% of the heat. Likewise a G-value of 0 would be in the case of a completely opaque material. The majority of windows, will have a G-value of between 0.2 and 0.7 depending on the type of glazing used.
Any other measures?
Yes there is! Another key rating is the air permeability. This is a simpler test, which involves measuring how much air can pass through a window at different pressures, in other words, how draughty is it (or isn’t)!
The window is the given a Window Energy Rating (WER) by the British Fenestration Ratings Council (BFRC), this is calculated by:
WER = Solar Gain – (U-value + air leakage)
To keep things simple, this is then show as a banded rating, which runs from A++ to G and displayed on a rainbow label – similar to the ones you would find on your fridge, freezer and other white goods.