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Heat flow in buildings
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Heat Loss in Buildings

We heat our homes to stay warm, no matter what is the outside temperature. If it gets colder outside, the inner temperature stays the same, but we need more energy to maintain that temperature. This is because heat loss is greater when the temperature difference between the inside and outside is larger so more heat is lost and we need to produce more heat to stay warm inside.

Windows are responsible for up to a quarter of the total energy loss either through the glass pane directly or by ventilation through any gap between the window frame and the wall. Single panes of glass are very good at allowing heat to be conducted from the hotter to the colder source. The larger the window area, the greater will be the heat transfer; heat loss in winter and solar gain in summer

Single panes of glass can also contribute to condensation during the winter as moisture condenses on the inside of the window.

High levels of condensation can contribute to health problems as these can create conditions in which house mites can flourish which can lead to bronchial illnesses such as asthma or allergies. So reducing heat transfer rates through windows has more than one benefit.

Typical heat loss in a building

Doors leading to the outside or to a balcony are fewer than windows and so contribute less to heat transfer, however the same principles apply particularly for glass doors.

Walls are the largest source heat loss because they represent the largest area in contact with the cold air outside. A ‘visible’ example of heat loss is the wall just behind the radiators in your room. The radiator, which is typically located very near the wall, is emitting heat not only towards the free space of the room, but also towards the wall. The wall is then heated and the heat is lost to the outside if the wall is not insulated well enough.

The heat loss is greatest for a detached dwelling which has the largest number of outside walls and least for an apartment in a multi-family dwelling.

Roof and floors
May be responsible for up to 35% of the total energy losses The exact number depends on the type and building and its level of insulation – the loss will be smaller in apartment buildings where most apartments have neighbours with heated flats above and below also and highest in individual homes.



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