Choosing the right U-value

U-value, a simple explanation… if it's cold outside and warm inside, U-value is the measurement of how quickly the heat from the inside leaks to the outside.

The term U-value or thermal transmittance is used as a standardized measure of how easily a component passes through heat. In technical talk, U-value is measured in W/m²K and indicates how much heat per unit of time that flows through an area of 1m² at a constant temperature difference of 1K (1°C) between warm and cold side of the structure. A well insulated building component has a low U value.

Both the glass and the frame are taken into consideration when calculating a product's U-value. We offer five U-values from 1.4 through to ‘Passive House’ compatible products in the low U-value of 0.7.

Choose a suitable U-value for your project by considering the overall energy efficiency of your home. Think about the type of walls, floors, doors, roofing and insulation. A period property with little or no wall insulation is likely to leak more energy than a property built in the last 10 years, therefore, a U-value of 1.4 or 1.2 will be appropriate as the overall heat loss from the property can only be countered so far with energy efficient windows. Similarly, fitting 0.7 U-value windows in a standard new build project will cost up to 50% more but will only reduce overall house heat loss by around 5%.

Broxwood product U-values

Comfort, Broxwood's entry level product, out performs the UK building standard requirement for new build projects.They are exceptional value and are suitable for new build and renovation projects.


Our EnerSave windows provide real savings and are ideal for new build or replacing windows in an older style property.


How well insulated is the rest of the building? Our EnerPlus windows are suitable for replacing windows in a properly insulated property or for a new build project.


Broxwood's technically advanced product is compatible for use in a Passive House project or a building where your overall intention is to be as carbon neutral as possible.


It is worth noting that the more ‘break points’ you include in your choice of window design the less energy efficient it becomes. Including astragals or vents for example, may slightly reduce overall energy-saving properties.

We want you to buy the right product. If you are in any doubt please contact Broxwood for independent technical advice.

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Broxwood’s passive house standard timber windows and doors provided the perfect solution for Findhorn’s ecovillage development. Read the Findhorn case study

U-values explained

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