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Air Conditioning Installation And Maintenance Guide

Central vs space heating

Choosing whether to heat your whole house or only the required rooms or spaces has a major influence on the greenhouse impact of your home. In a house with central heating, the greenhouse emissions and costs of running it are usually higher than running efficient space heating.

Central heating can often heat a whole house whether individual rooms are occupied or not. Space heaters usually only heat the room or area where the heater is installed.

For an energy efficient house, use space heating only in rooms that require heating or use a zoned central heater to reduce running costs.

Heat only the rooms that are being used.

Answer the following questions before buying a heater:

  • Does the room need to be heated or will eliminating cold draughts and improving insulation be enough?
  • How many rooms need to be heated?
  • How big are they?
  • How often and for how long will heating be required?

The Choice online guide (www.choice.com.au) helps work out which heater is right for your home. Seek expert advice to find a system most suited for your application.

Central heating

Central heating usually uses more energy than space heating as more of the house tends to be heated. However, an energy efficient house with central heating may use less energy than an inefficient house with space heating. Several types of central heating are available.

Many central heaters have high energy losses from the heat distribution systems, usually through ducts or hot water pipes. They should be as short as possible and well-insulated (at least R1.5 for ducts and 25mm of pipe insulation). Fans and pumps can also be costly to run. When heating requirements are low, distribution losses can be the main contributor to heating costs.

In well-insulated houses with solar gain to some rooms, a central thermostat may not provide comfort throughout: some rooms may have higher heat losses and cool down faster than the rest of the house.

Ducted air

In ducted systems, hot air is circulated through roof or underfloor ducts, supplying convective heat. Gas or a reverse cycle air conditioner can be the heat source.

Design the system so that the extent of the area heated can be controlled and include zoning to allow for shutting off heating to unoccupied areas. Ducted systems should be designed and installed by accredited experts.

Ensure the ducted system is sized for the house. New, energy efficient houses that meet the requirements of the Building Code of Australia (BCA) require less heating and smaller capacity heating equipment.

Ducts should be the correct size and have adjustable outlets (registers). Ducts need to be larger if also used for cooling.

Insulate ducts to at least R1.5 and make sure all joints are well sealed. (see Insulation)

Floor outlets are often better than ceiling outlets for heating, as warm air naturally rises and they deliver heat to where it is most needed. Well-designed ceiling outlets can work well particularly when rooms are sealed from draughts to the outdoors. Cold air entering under outside-facing doors can form a layer above the floor and stop the less dense warm air from ceiling vents heating the air near the floor, creating a ‘cold feet–warm head’ problem.

A return air path from every outlet back to the central system is very important. Without it the warm air escapes and the system sucks cold air in, dramatically reducing its effectiveness. In each room that has a duct outlet installed, a gap under the door between the room and the central return air inlet creates a return path.

In ducted gas systems, a fan moves the air around the home, using electricity as well as gas. High efficiency ducted gas systems use more efficient motors/fans, and control the fan speed, to reduce electric running costs.