Energy

In central heating systems, heat is supplied by a single unit and ducted to outlets in the floor or ceiling of rooms/spaces inside the house. Most central heating systems use hot air, though heated water can also be used. Central heating options can include central air conditioning units. Separate room heaters are more common than central heating for domestic heating.

Most central heating systems use gas or electricity, but some use energy efficient sources such as waste heat recovery or the absorption of passive heat (for example, solar radiation).

Though both air and water have reasonable heat storage capacity, there are always some energy losses between the heating unit and the room. These heat losses can be reduced by minimising the length of duct/pipe run, minimising cross-section area, maximising flow rate, improving insulation, and running the ducts/pipes through spaces with warmer temperatures.

A central heating system has a slower response to changes in room heating requirements. The delay will increase with longer duct/pipe runs, and will be greater in systems using water to transfer heat from the plant to the rooms.

Central heating involves a significant up-front capital cost compared with room heating options. An efficiency of 70 to 90% (depending on the system specified) can be achieved.

Advantages and disadvantages of central heating

Central heating can provide more effective and energy efficient convective space heating when:

• rooms have individual thermostatic control
• there are a number of rooms with similar heating requirements regarding temperature and times that heat is needed
• one central heating unit can be used instead of a number of room heaters
• energy efficient heat sources can be used to power the central unit (for example, solar panels, heat pumps)
• the combustion of gas, oil or solid fuel is isolated from the heated space.

Drawbacks of central heating include:

• installation costs
• limited control over heat output within each individual space without suitable feedback from each space (for example, separate thermostats)
• a time delay before heat output is changed to meet heating demand
• limited flexibility (in terms of moving or resizing components) to meet changing heating requirements
• the need for space to house the central heating unit
• the need for suitable routes for pipes and ducts.

For your clients

To help your clients make decisions about space heating options, refer them to www.smarterhomes.org.nz/energy/heating.