What's What - Energy Efficiency in Window Technology

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What's watt - where do they go? Windows may as well be plugged into your power point going by the amount of watts they use. In energy terms, compared to bricks and mortar, windows are just holes in the wall which allow heat to move via conduction from the hot side to the cold side. The amount of heat they allow through can be predicted in a measure called window U value (or U factor). The U value of a window measures energy loss in watts per square metre per degree Celsius passing through the window, which of course shows up in your power or gas bill just like the watts of your electric kettle or iron! If a house was perfectly insulated it would require zero heating or cooling to maintain temperature equilibrium, so what we pay for in gas and electricity for heating and cooling is directly related to how much energy leaks into or out of our homes. The better a home is insulated, the less energy we need to keep our home at a comfortable temperature. Windows play the biggest part in the cost of that energy, like a leaky boat whose hull is watertight apart from a few holes - we must bail the water at a rate that is equal to the rate of the leak or the boat will sink; so too with windows and doors, we must replenish the heat gain or loss from our windows by turning on the heating or cooling to remain comfortable. Since a window’s U value is a measure of the window’s ability to conduct heat, then the lower the U value the higher its insulation or heat stopping properties. For U value, lowest is best. If we compare two windows, one with a U value of 3 and one with a U value of 2.7, then the window with the U value of 2.7 stops 10% more heat from being conducted through the whole window and requires 10% less energy to maintain the comfort level compared to the window with the U value of 3, that is 10% less in your heating or cooling bill for that window (looking

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