Energy

With central heating systems, heat supplied by a single unit is circulated to multiple rooms inside the house. Heating may come as warm air through floor, ceiling or wall outlets, or warm water passing through underfloor pipes, radiators and even towel rails.

Systems are tailored to meet the needs of the individual house. They are not common in New Zealand. The BRANZ 2015 House Condition Survey found central heating in fewer than 5% of its random sample of 560 houses. Part of the reason for this is that so many New Zealand houses have such poor levels of insulation that operating a central heating system can be expensive because of the heat loss.

Most central heating systems use gas or electricity. Gas boilers are cost-effective in those parts of the country where reticulated natural gas is available. LPG boilers usually have the highest running costs – twice the cost of natural gas (measured as cents per kWh) is not unusual. Some systems use compressed wood pellets or energy-efficient sources such as heat pumps, waste heat recovery, or the absorption of passive heat (for example, solar radiation). The cost of wood pellet central heating (cents per kWh) falls between natural gas and LPG.

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 upfront capital cost compared with room heating options. An efficiency of 70–90% (depending on the system specified) can be achieved.

Central heating suits families with small children, elderly people and people with a disability or long-term illness. The lower-temperature heat sources in each room are safer than high-temperature appliances, with a reduced risk of burns.

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 or heat pumps)
• the combustion of gas or solid fuel is isolated from the heated space.

Drawbacks of central heating include:

• installation costs – $8–15,000 is common for a small to medium-sized house
• 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.

Systems are available that provide hot water for household needs as well as for the space heating system.

Where central heating is being considered as a retrofitted heating option for an existing home, first ensure that there are sufficient levels of thermal insulation in the house.

More information

• www.smarterhomes.org.nz – heating

Updated: 23 August 2021