# 2.1 Heating a house

Although it is common to think of a house being heated solely by some form of heating system, in practice it is likely to be warmed by energy from three sources:

- the heating system
- ‘free heat’ gains − from occupants, lights, appliances and from hot water use
- passive solar gains from solar energy penetrating the windows.

In a really low-energy house design, free heat and solar gains may provide more useful heating than the heating system itself.

Obviously in order to achieve a low overall space heating demand it is necessary to reduce the heat losses. Figure 4 shows a small house and illustrates the ways in which heat flows into and out of a house. The losses are particularly important. There are:

- fabric heat losses − those through the building fabric itself, i.e. the walls, roof, floor and windows
- ventilation losses − due to air moving through the building
- flue heat losses − since the heating system is not 100% efficient.

These basic losses also apply to larger buildings.

Figure 4 Heat flows through a house

There are three ways of reducing the space heating energy use discussed in this course:

1. cutting the fabric heat losses by the use of insulation (Section 2.2)
2. cutting the ventilation loss by making the building more airtight and possibly using mechanical ventilation with heat recovery (Section 2.3)
3. installing a more efficient heating system (Section 3).

OpenLearn - Energy in buildings
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