Heating, cooling and hot water

The stakesWhere a home's energy goes

Heating accounts for about 60% of the energy used in an average Canberra home. Heating water comes next. Cooling is a much smaller share in Canberra.

Appliances like these last around twelve years on average, so the choice you make during design fixes your running costs for a long time. It also fixes the fuel. Since December 2023, new homes in the ACT can't be connected to gas. The ACT is moving away from gas altogether, so a new gas appliance in an existing home may not get to serve out its full life. In NSW, gas is still allowed, but the long-term direction is the same.

The house comes before the equipment. A well-insulated, well-oriented seven-star home needs a much smaller heating system than an older house of the same size, and a smaller system costs less to buy and to run. Get the design right first, then choose the equipment to suit it.

Heat pumpsWhy reverse cycle is the default

A reverse-cycle air conditioner is a heat pump. It doesn't make heat by burning fuel or heating an element. It moves heat that's already in the outside air into the house, even on a cold night. That's why it gives out more energy than it uses. A good system delivers 2.5 to 6 units of heat for each unit of electricity, a measure called the coefficient of performance (CoP). A plug-in or panel heater delivers exactly one. A gas heater delivers less than one, because some of the heat goes up the flue.

Here is what that means for heating a 50 m² living area in an older Canberra home for a year:

Energy prices change, but the gap in energy use doesn't. The efficient reverse-cycle system uses about a sixth of the energy of the panel heater.

The same unit cools the house in summer, so one system does both jobs. Good units keep heating effectively down to about −10°C. On frosty mornings the outdoor unit stops heating for a few minutes every so often to melt ice off its coil. That's normal.

ChoosingSplit, ducted or multi-head

There are three common ways to set up reverse-cycle heating and cooling:

• Split systems suit single rooms and open-plan living areas. A larger unit can serve up to about 80 m². In houses under about 180 m², a few well-placed splits are usually the most cost-effective choice. Smaller units also tend to be more efficient than large ones.
• Ducted systems suit larger houses that need every room conditioned. Their weak point is the ductwork. Ducts in the roof space sit outside the insulation, where they lose heat in winter and gain it in summer, and they often squash or displace the ceiling insulation around them. If you choose ducted, insulate the ducts to at least R1.5, and where you can, design bulkheads or floor voids that keep the ducts inside the insulated part of the house. Old gas heating ducts can't be reused, because they're too small for reverse cycle.
• Multi-head systems sit between the two, with separate indoor units in each zone running off one outdoor unit.

Read the right label. Air conditioners carry a Zoned Energy Rating Label with separate star ratings for hot, average and cold climates. Canberra is the reference city for the cold zone, so compare models on their cold-zone heating stars, and compare models of similar capacity. The label also shows how loud the outdoor unit is.

Size it to the house, not the floor area. An oversized system costs more to buy and runs less efficiently, because it keeps switching on and off. Ask for a heating and cooling load calculation based on the actual design. The energy rating already models how much heat each part of the house needs, which is a good starting point.

Other optionsHydronic, panels, wood and fans

• Hydronic heating circulates warm water through wall panels or pipes in the floor slab. The heat is gentle, silent and draught-free. In a new ACT home the water has to be heated electrically, and a heat pump is the efficient way to do it. In-slab systems respond slowly, taking hours to warm up or cool down. They suit homes that are occupied all day more than homes that are empty until evening. Wall panels respond faster. The slab must be insulated underneath and at its edges, or much of the heat goes into the ground. Hydronic systems cost more to install and don't cool.
• Electric panel heaters, heated towel rails and electric in-slab cables turn electricity into heat one for one. They cost three to six times as much to run as a heat pump. They're fine for small, brief jobs like warming a bathroom, but they shouldn't be the main heating.
• Wood heaters put smoke into the neighbourhood, and in a well-insulated house they easily overheat the room they're in. Check local rules before you plan one.
• Evaporative coolers work well in dry heat, but they use water, need open windows and do little on humid days. They can't heat, so in a new home with reverse-cycle heating they're rarely worth adding.
• Ceiling fans are the cheapest cooling there is, and the moving air makes a room feel cooler without changing its temperature. In winter, a fan on low speed in reverse pushes warm air back down from a high or raked ceiling.

Hot waterA heat pump for water too

The same principle applies to hot water. A heat pump water heater uses 55% to 80% less energy than an electric storage or gas system.

• Choose one rated for frost. Some heat pumps struggle near freezing and fall back on an electric element, which wipes out most of the saving. Check the operating range on the datasheet. Units using CO2 as the refrigerant are designed for cold climates, and some operate down to −10°C. Others are rated to around −5°C with a de-icing function.
• Run it in the middle of the day. Set the timer so the heat pump runs in the late morning and early afternoon. The air is warmer, so it works more efficiently, and it can use your own solar power. Daytime running also keeps the noise away from bedrooms at night.
• Size the tank to the household. As a guide, about 180 litres suits two people, and about 270 litres suits three to five, depending on the number of bathrooms and how long the showers are. A tank much bigger than you need wastes heat keeping water you don't use hot.
• Put it close to the bathrooms and kitchen. Every metre of pipe between the tank and the tap is water you run off and heat you lose while waiting for hot water. Insulate the pipes. Split heat pumps, with the tank indoors and the compressor outside, lose less heat from the tank in a cold climate.
• Keep it safe. Stored water must be kept at 60°C or more to control Legionella bacteria. A tempering valve then limits water to bathrooms to 50°C to prevent scalding.

Evacuated-tube solar hot water also works in sub-zero weather, but it still needs a booster for cloudy winter days, and it takes roof space that's usually better used for solar panels.

DeliveryPlanning it, building it, running it

• Show the equipment on the drawings. Mark the model and capacity of each unit, the outdoor unit locations, the hot water system, the duct or pipe routes, and the condensate drains. If it isn't drawn, it gets decided on site.
• Check the power supply early. An all-electric home with a ducted or multi-head system, a heat pump water heater, an induction cooktop and an electric car charger may need a larger switchboard or a three-phase supply. That's cheap to plan and expensive to retrofit.
• Match what's built to what was rated. The NCC Whole of Home rating, which needs a score of at least 60, counts the heating, cooling and hot water you choose. Swapping in a less efficient system during construction can change the result.
• Set it and zone it. Set the heating thermostat to 18–20°C. Each degree lower saves up to 10% of heating costs. Heat only the rooms in use, and close the doors between zones.
• Look after it. Clean the filters on indoor units regularly, keep the outdoor unit clear of leaves and plants, and have the system serviced as the manufacturer recommends.