What is the U value?

Double glazing can be measured on its enery efficiency whilst comparing it to other windows, by using a calculation system known as the U value (or U factor).

The U value can be adopted for any kind of home construction and measures how effective that component is at retaining heat. Importantly, the lower the U value, the more proficient the window is at saving energy.

Double glazed windows and double glazed doors will have a much lower Uvalue than standard single panes.
What are the benefits of measuring double glazing with the U-value?

Above all, installing new windows that are fitted with double glazing reduces heat loss, which in turn leaves a smaller carbon footprint as carbon dioxide emissions are cut by up to 50%.

Measuring single or double glazed windows will highlight where in your home heat loss is increasing your energy bills.

Of course, double glazing is also installed to reduce noise pollution and improve security, but the U value only incorporates heat loss in its calculations.

What are the standard U value measurements?

The nationally recognised rating method for double glazed panels is for the whole window, including the glass, frame and spacers. However, sometimes a centre-of-glass U Value is given, which simply measures the performance of the glazing alone.

It is common for double glazing companies to cite the stand alone heat reduction in just the pane, so always double check how much heat will be lost for the rest of the window frame as well.

Below are the general U values for varying glazing standards:

  • Single glazing U value = 5.6 w/m2K (Watts / square metre Kelvin).
  • Double glazing (with air cavity) U value = 2.8 w/m2K.
  • Double glazing (with argon gas cavity) U value = 2.6 w/m2K.
  • Double glazing with low emissivity glass (with air cavity) U value = 1.8 w/m2K. Double glazing with low emissivity glass (with argon gas cavity) U value = 1.5?? w/m2K.

How to measure the U value

Measuring your home?s heat loss is not as complicated as you may think. Using the above mentioned U-values, you can quickly measure how efficient your double glazed doors and windows really are.

The following formula can be used to determine each window?s heat loss at any time of the year:

Glass Width x Glass Height x U Value x Temperature difference from inside to outside = Heat loss per hour (Watts).

By measuring every window in your home, you can quickly and easily work out how much energy is being wasted and eradicate the problem.

What is the difference between the U Value and the R value?

The U value is used only in measuring the insulation of windows, while the R value covers all other aspects of the home, including walls, floors and roofs. There are many factors when calculating the R-value for heat loss for any given wall and R values only apply to properly installed insulation.




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