Depending on where you live, you may only need a central cooling or a central heating system. In this case, a ducted reverse-cycle air conditioner may be overkill and a specialised system may be more appropriate.
All central systems need expert advice regarding the capacity and installation required for your individual situation. Your state energy authority may have more information on these systems.
Central cooling-only systems
An evaporative air cooler consists of a motor driven fan, a dust filter, a water tank and a wetting medium. The hot air is drawn across the wetting medium, which is saturated with water from the tank. The water evaporates, absorbing heat from the air, and cooler, moist air is blown into the room.
Evaporative air coolers provide relief from dry heat. If you live in a humid climate, such as parts of coastal Australia, they won’t do you much good — you’ll need an air conditioner. And if you live in a place where temperatures get very high, you may not find one satisfactory either. If you're trying to cool a room down from the low forties, you're unlikely to get it much below 30 degrees Celsius - and unfortunately, it'll be a pretty humid 30 degrees because of the moist air created.
Evaporative coolers are cheaper to buy and run than air conditioners.
With ducted systems, the main unit is installed in the roof, and the cooled air is ducted into the rooms via ceiling outlets. It can use up to 25 L of water per hour, so this type of cooling may not be the best choice if you live in a water-restricted area.
Central heating-only systems:
Ducted gas air heating
Air is heated in a central gas heater (look for an efficient model with a high gas star rating) and distributed through insulated ducts to ceiling, wall or floor panels throughout the house (similar to ducted air conditioning). Different areas can be zoned, each with its own individual thermostat.
This type of heating can circulate a lot of dust (requiring a filter system that adds to the running costs and maintenance requirements), and tends to dry the air.
With this system, water is heated in a central boiler, then circulated around the house to panels that radiate and convect the heat to the air. The boiler can be fuelled by natural gas, LPG, wood or off-peak electricity.
The panels are usually individually controlled, so you can adjust the temperature of each room according to your needs. Look for quick-response panels made from mild steel and with a relatively small volume.
This type of heating is very quiet and circulates only a little dust.
With this type of heating, the concrete floor slab is heated by internal electric cables or hot water pipes. It’s not recommended for suspended concrete floors where the space underneath isn't occupied, or for slab-on-ground in areas with a high watertable. And you’d probably only choose it if you’re building a new home or an extension.
Electric systems run on off-peak electricity, hot water systems can be fuelled by natural gas, LPG or wood.
This type of heating takes a long time to respond to changes in the thermostat setting, so it’s often left running 24 hours a day on an appropriate setting — making zoning (separate thermostatic controls for different parts of your house) very important.
Running costs and greenhouse gases
With all central heating systems, running costs depend very much on what fuel type you’re using and how much you pay for it. Compared to ducted reverse-cycle air conditioning, all types of natural gas heating are likely to have lower running costs, while using LPG and electric hydronic heating are likely to be more expensive to run.
Using natural gas or LPG produces much less carbon dioxide than reverse-cycle air conditioning, while electric heating produces considerably more.
For more detailed info, check the Sustainability Victoria factsheets.