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Window Energy Ratings Applies to L1b

Window Energy Ratings calculate the “energy balance” of a typical window by combining the heat losses and offset against heat gains due to the sun.

The resulting energy balance, the difference between the gains and losses is the Window Energy Rating expressed in kWh/m² per Year. Window with high solar gains can completely offset the heat losses from the window resulting in a windows which is a net heat contributor to the property. The values used to calculate the energy balance are based on typical values of sunshine and climate for the UK for a typical window.

Understanding 'WER'

The ratings are from A to G with A being most efficient and G rated windows losing the most amount of heat. Band A is a window where the solar gains are larger than the heat losses, band B to G the window will lose heat. The energy balance is calculated for a typical year in the UK and calculates the energy in kWh per square metre of window. The effective cost for the typical window would depend on the cost of heating and number of windows. The following table shows typical annual savings based on the cost of gas heating for different sized properties.

Example
A detached house with PVCu window 8 years old replaced with C Rated Aluminium Windows, the heat losses would drop from £100 per year to £19 saving £81 per year.

Source: GGF Energy Saving Calculator Based on Gas Heating
Heating costs Gas 0.04 £/KWh, Electric 0.083 £/KWh, Oil 0.061 £/KWh, Solid Fuel 0.027 £/KWh

Window Energy Rating

WER window energy rating bands (Domestic Windows Only) The ratings are classified into bands A-G representing bands of WER Ratings kWh/m²/yr. Windows with a net heat loss have BFRC rating bands B-G windows with an A rating indicating a net inflow of heat, warming the property. Window energy rating are based on the energy balance of the losses through the window offset against the solar heat gains through the window. The calculations are always on standard designs and based on typical climate data for the UK. Window energy ratings are intended as a comparator tool and the actual heat losses on the window will depend on the location design of window and climate. Only applies domestic building s L 1b re furbishment only . WER may also apply to commercial re-furbishment, if the building is domestic in character.

For example, student accommodation, care homes and similar