Heating and cooling

Key points

  • The best heating and cooling system is one that suits your climate, the size of your home, and your lifestyle.
  • Having the right sized system for your home will save you energy and money. Buying a system that is too large or small will mean you will use energy unnecessarily and pay more in the long run.
  • You can choose a central heating or cooling system, which acts to heat or cool most or all of the rooms in your home, or a space heating or cooling appliance, which heats or cools one area or room.
  • Combined heating and cooling options can be used for heating in winter and cooling in summer. They include reverse cycle air-conditioners, hydronic systems and ground-source heat pumps.
  • Heat pumps (including reverse cycle air-conditioners) are the most energy-efficient combined heating and cooling system you can buy.
  • Central heating options include ducted air and in-slab floor heating. Space heaters can use electricity, gas or wood.
  • Central cooling options include air-conditioners or evaporative coolers; space cooling options include fans, or portable air-conditioners and evaporative coolers.
  • Set your thermostat correctly. Each degree of extra heating in winter or cooling in summer increases energy consumption by about 5 to 10%. Set the thermostat to 18 to 20°C in winter and 25 to 27°C in summer.

Understanding heating and cooling

Heating and cooling together use the largest amount of energy in the average Australian home, accounting for around 40% of household energy use. So it is important to prioritise your investment when it comes to keeping your house comfortably warm or cool.

If you are building a home, the best long-term option is to use passive design principles to minimise your heating and cooling needs. This should be combined with smart household behaviour. There are many free and low-cost strategies you can use to get the most out of your heating and cooling appliances. It is also important to choose the right system for your circumstances, to maximise your comfort for the lowest possible cost and environmental impact.

A bar graph shows that heating and cooling accounts for 40% of a households energy use. Appliances account for 25%, water heating accounts for 21%, lighting accounts for 7% and cooking accounts for 5%.

Percentage of household energy use

Source: Energy Consult (2015)

Climate

Your first consideration in making heating and cooling decisions for your home will be your climate. Do you need more heating, more cooling, or a balance of both?

Consider what changes you can make to your home to improve its thermal performance. Improving your home’s thermal performance may mean that you do not need as much heating or cooling as you think.

Sizing

One of the most important tips for buying a heating or cooling appliance, is to buy one that is correctly sized. If you buy a one that is too large for your needs, it will cost you more money and you will waste energy and money in operating it. If you buy one that is too small, the appliance will need to run ‘harder’, using more energy to keep the room at the desired temperature.

Consider the area in your home that you want heated or cooled; how often and for how long is heating or cooling needed? For example, if temperatures in your climate zone fall sharply at night, you may only need to cool a small living area during the heat of a summer day, then open the bedrooms to cooling breezes at night.

Central versus space

Central heating and cooling systems are designed to heat or cool a whole house (for example, through ducted vents in most or all the rooms). Space heating and cooling systems have a single source of heating or cooling, and are designed to heat a small area or one room.

Choosing between central heating and cooling systems, or appliances that heat or cool individual rooms or spaces, is an important consideration for your home. If rooms are unused or a home is mostly vacant, central systems can often waste energy by conditioning empty spaces. For an energy-efficient home, using a space heating or cooling device only in rooms where it is needed, is the best option.

Some central systems have zone settings allowing heating or cooling to be switched on or off in different sections of the home that are used less frequently, which can make them more efficient.

Another alternative is to use a combination of systems. For example, you may wish to have a central system that heats and cools the main living areas of your home, but then use electric space heaters for brief times in a bedroom or study.

Choosing heating and cooling

Some systems combine heating and cooling options and you can switch between them depending on the season. Others offer only heating or cooling. Your choice will depend on both your climate and the thermal performance of your home.

Combined heating and cooling options

Reverse cycle air-conditioners

A reverse cycle air-conditioner uses electricity to warm your home in winter and cool it in summer. An air-conditioner is a type of heat pump (refer to Heat pumps below). In heating mode, the system absorbs heat from the outside air and distributes it around the room. In cooling mode, it absorbs heat from indoor air and releases it outside.

If you are thinking about buying an air-conditioning system, it will have an energy rating label which tells you how efficient the appliance is, relative to other models of the same size. The zoned energy rating label gives an efficiency rating for different seasons for 3 Australian climate zones, so you can understand how the appliance will perform in your home. For more information about energy rating labels, visit the Energy Rating website. Air conditioners also have to meet Minimum Energy Performance Standards, set by the Australian Government.

Reverse cycle air-conditioners provide convective heat and are the most energy-efficient heater and cooler of all types, irrespective of fuel source. Even the lower efficiency rated units (for example, 2 to 3 energy stars) are significantly cheaper to run and generate less greenhouse gas emissions than other heating and cooling appliances.

Two images, the first is of two outdoor units attached to an external wall, connected to a split system. The second image is of a reverse cycle air conditioning unit on a wall inside a home.

Reverse cycle air-conditioner – external unit

Photo: www.energyrating.gov.au

Two images, the first is of two outdoor units attached to an external wall, connected to a split system. The second image is of a reverse cycle air conditioning unit on a wall inside a home.

Reverse cycle air-conditioner – internal unit

Photo: Maeli Cooper

Hydronic systems

Hydronic systems circulate hot or cold water or other fluid through radiator panels in rooms or under the floor (refer to In-slab heating below).

The fluid may be heated or cooled by electric or solar pumps, or by gas if used for heating only. Solar systems can use gas, wood or electric heating as a back-up.

Hydronic systems are typically more expensive to buy and install compared with space heaters. Ensure water circulation pipes are well insulated, and use smart controls to manage pump usage. Higher running costs are usually caused by unnecessary water circulation or poor pipe insulation. Exterior walls behind panels must also be insulated to prevent heat or cool loss to the outside. Use wall cavity insulation or a layer of installed reflective foil on the internal wall behind the radiator panel.

Heat pumps

There are 3 types of heat pump: air-source, water-source, and ground-source. Each of these pumps uses a heat exchanger to extract heat from the air, water or ground, respectively, to heat the home.

An air-source heat pump is also known as a reverse cycle air conditioner – it extracts heat from the air to heat the home (refer to Reverse cycle air-conditioners below). These are some of the most common and efficient heating systems in Australia. Australia does not generally have appropriate water resources to use water-source heat pumps. Ground-source heat pumps can operate efficiently in extremely hot or cold conditions. However, they remain expensive for most residential applications in Australia and uptake is still limited.

For ground-source heat pumps, pipes are run deep into the ground where the temperature is stable all year round. This means that such systems can be used for cooling in summer and heating in winter.

Air is pumped through the pipes and cools or warms as it passes through the ground. The pipe system needs to be extensive enough to give the air enough time to change temperature as it travels through the pipe. It is then pumped back inside the home.

If the system is used alone to cool the air in a home, special precautions will need to be taken to prevent mould in the pipe, which can result as the cooling air causes condensation. Alternatively, ground-source heat pumps can be used as an adjunct to air-conditioning, to precool the air to make the air-conditioner more efficient. Air-conditioning refrigerant can also be pumped through the pipe to achieve the same effect. In winter, the system can also be used to preheat the water for hot water systems.

Two diagrams of the same house with a geothermal exchange system running through the ground which is at a constant temperature of 17-19 degrees centigrade. In winter: Cool water flows from the house unit through the subterranean pipes absorbing heat from the ground, returning to the house unit as hot water. In summer: hot water flows from the house unit through the subterranean pipes radiating heat to the ground, returning to the house unit as cooled water.

Ground-source systems are very efficient heat pumps

 

Heating options

The 2 main forms of heating are radiant and convective. Radiant heaters predominantly heat people and objects by direct radiation of heat. Convective heaters warm and circulate the air in a room through convection. Less common forms of heating, such as heated floors, also heat by conduction through direct contact with a person.

Different forms of heating are best in different circumstances:

  • In larger rooms with high ceilings, a combination of radiant and convective heating is best.
  • In small rooms, space convective heating is effective.
  • In larger draughty rooms or bathrooms, radiant heating works best.

Central heaters use convection; space heaters use radiation or convection or a combination of both.

Refer to Passive heating for ideas on making your home warmer.

Ducted air heaters

In ducted systems, hot air is circulated through roof or underfloor ducts, supplying convective heat. These systems can use gas or electricity, and electric systems may also be used for cooling (refer to Reverse cycle air-conditioners below).

Floor outlets are often better than ceiling outlets for heating, as warm air naturally rises and floor outlets deliver heat to where it is most needed. Ceiling outlets can work too, particularly when rooms are sealed from draughts to the outdoors. If cold air enters under outside-facing doors, it 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.

Just as for any heater, ensure the system is sized for the house. Ducts should be the correct size and have adjustable outlets. Ducts need to be larger if also used for cooling. 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.

When used for heating, a return air path from every outlet back to the central system is 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.

If your ducted air-conditioner is powered by electricity, it will have an energy rating label that tells you how efficient the appliance is, relative to other models of the same size. The zoned energy rating label gives an efficiency rating for different seasons for 3 Australian climate zones, so you can see how the appliance will perform in your home.

In-slab floor heating

In-slab floor heating uses hot water pipes or electric wires or mats that are laid either in a concrete slab or in the concrete topping to a slab and provide heating to living spaces. They are installed during building construction or renovation.

In-slab systems provide a combination of radiant, convective and conductive heat. They are slow to warm and cool due to the high thermal mass of the slab and are therefore unsuitable for houses where heating is needed only occasionally or for short periods or in changeable weather. They are ideal as back-up for passive solar heating of thermal mass on cloudy or extremely cold days. If you heat the slab then its ability to store heat from passive solar gain is reduced.

Electric in-slab heating generally has the highest energy use of any heating system. As electricity prices have increased, in-slab heating costs have also increased. The best in-slab system for minimising greenhouse gas emissions is a hydronic system using solar with gas back-up (refer to Hydronic systems above for more information). An efficient slow combustion wood heater that heats the water using a wetback system is also an option. These are becoming less popular due to concerns for public health associated with particulate emissions from wood smoke (refer to Wood heaters below for more information).

Heating zones and thermostats are essential to reduce energy use. Slab insulation is also important, so that heat from the slab does not leak into nearby cold earth. Insulate concrete slab edges, and ideally the entire slab, from the ground to minimise heat loss.

Electric space heaters

Electric portable heaters

Note

Electric portable heaters can be cheap to buy but are expensive to run and sometimes ineffective.

Heaters that do not rely on fans or reach high temperatures are more suited to bedrooms, as they are less likely to overheat and cause fires if clothes are accidentally placed on them. All electric heaters should have a safety cut-out to avoid overheating.

There are various types:

  • Radiant heaters, such as bar heaters, are better for bathrooms as they give almost instant heat direct to your body and do not directly heat air. Turn off radiant heaters when leaving the room for any length of time. Radiant heaters do not generally have a thermostat, so use a timer or switch.
  • Fan heaters heat the air and provide convective heat. Larger upright models are more effective. They can warm smaller rooms quickly and some have thermostats to help reduce energy use.
  • Convection heaters heat the air, which then rises naturally and circulates through the room. They are not recommended for rooms with high ceilings or poor insulation levels or where there is a high ventilation rate.
  • Combined convection–radiant heaters are larger than fan convector units, and may have a small fan to increase heat output. They have a large surface that becomes hot and radiates heat, as well as slots to allow heated air to rise into the room.
  • Oil-filled column heaters supply a mix of convective and radiant heat, but can be slow to warm up once switched on. Some have thermostats, timers and fans.

A thin rectangular-shaped metal heater with vents at the top to release heated air which warms the room.

Convection heater

Photo: Maeli Cooper

Electric fixed storage heaters

Off-peak electric storage heaters provide a mix of radiant and convective heat. They use a ‘bank’ of high-density ceramic bricks to store heat that is produced overnight using off-peak electricity. They now have built-in smart features, thermostats and timers to ensure heating is turned on only when needed. Unless carefully controlled they can lead to overheating in milder weather.

Gas space heaters

Portable gas heaters

Portable gas heaters can provide either convective or radiant heat and produce heat through the combustion of natural gas or LPG (liquefied petroleum gas). These heaters are unflued, which means the gases produced by combustion are not removed via a chimney or flue, but are released into the space in which they operate. Adequate ventilation is needed to maintain good air quality, which reduces their heating efficiency.

Unflued gas heaters can be a risk to health when they are not used properly or not serviced regularly. The use of unflued heaters is restricted in some Australian states because of the hazard posed by indoor air pollution. Check your state or territory regulations for details.

Unflued gas heaters also often create condensation problems, usually at the opposite (coolest) end of the house. Care is needed to ensure the condensation does not lead to mould growth.

Gas fixed heaters

Gas fixed heaters include wall units and gas stoves. These can provide convective and radiant heat, and usually have fans to circulate hot air. Most are flued, requiring less ventilation and producing fewer condensation problems.

Some fixed gas heaters use ‘balanced’ flues with an outer and inner pipe: the outer pipe draws in outdoor air to burn, then the inner pipes remove waste gases to the outdoors. Other gas heaters use indoor air for combustion, and use the flue to only remove the waste gases from the house. In well-sealed houses, there is a small risk with gas heaters that waste gases can be drawn back into the house through exhaust fans (for example, kitchen range hoods or bathroom exhaust fans), if the gas flue is near the outlets of these fans. Take care when designing your home to ensure a reasonable distance between flues and outlets.

Some gas heaters have humidity trays which can be used to increase room humidity levels in low-humidity climates. This can help make rooms feel warmer and cosier. These heaters work by evaporating water into the space being heated and need to be topped up with water regularly.

Tip

Check carefully before you install a gas fire to ensure it is certified under Australian Standard AS 4553-2008 Gas space heating appliances.

Gas decorative appliances

Some log or flame effect fires are actually decorative appliances and are not designed to provide space heating. They can use up to 75MJ of gas per hour (2 to 4 times as much as a gas space heater) without giving effective heating. If you have a decorative appliance, use it only occasionally.

Decorative appliances are certified under Australian Standard AS 4558-2011 Decorative gas log and other fuel effect appliances.

Wood heaters

If using wood for heating, get a good fire going as quickly as possible to allow the heater to draw air and function properly, with little smoke production. If collecting wood yourself, ensure that you check local government regulations regarding firewood collection. If purchasing, always ensure it is dry, untreated wood from sustainable sources (that is, the carbon lost through burning is replaced by an equivalent amount of regrowth). Load firewood with approximately 25mm gaps between the logs to let in adequate air and help to develop pockets of glowing coals. For more information on reducing wood smoke emissions, a useful guide can be found at the NSW Environment Protection Authority.

Because of concerns for air quality and efficiency, many state governments and local councils are offering financial incentives to replace residential fireplaces with electrical and gas heating. Check the websites of your local state government and council for current offers.

Open fireplaces

Open fireplaces give radiant heat but are inefficient. Up to 90% of the heat goes up the chimney and large volumes of cold air are drawn into the room to replace it, creating cold draughts or removing heated air from nearby spaces where other heating is running. They are the least-efficient wood heating method and produce the highest levels of air pollution. Metal fireplace inserts can make an open fire slightly more efficient, but still around 70% of heat will be lost.

To comply with the National Construction Code, fireplaces should have closable dampers (that is, flaps that, when closed, stop air escaping up the flue). Many older units do not have dampers, although they can be retrofitted. Seal fireplaces when they are not in use to prevent heated (or cooled) air escaping from the room.

Inspect your flue or chimney once a year for blockages such as bird nests or creosote build-up, and have it swept if necessary.

Slow combustion heaters

Slow combustion heaters may be a free-standing stove or built into a fireplace. Slow combustion heaters and stoves are often fitted with fans and supply convective and radiant heat. They can be up to 85% efficient. They are most suitable for large spaces that need heating for long periods — they can take a long time to heat up and cool down. Many can be fitted with a wetback to heat water.

Operating slow combustion heaters with the air supply closed off usually causes high pollutant emissions and should be avoided to minimise air quality issues.

All slow combustion stoves must comply with Australian Standard AS/NZS 2918:2001 Domestic solid fuel burning appliances – installation.

A stand-alone slow combustion stove made from metal.

Slow combustion stoves are far more efficient than open fireplaces

Photo: Getty Images

Heat shifters

Heat shifters move air from warm areas to cooler areas. They consist of a fan and ducting, and cost little to run and install.

Heat shifters can supply heat for rooms that only require low levels of heating at some times of the day, such as bedrooms. They can also redistribute back downstairs, the warm air that collects upstairs, or warm air from the ceiling back down to floor level.

Make sure the fan is not left running when not needed, and that there is a return air path back to the heat source.

A diagram of a single level house shows how warm air is drawn across a room from a heater into an insulated duct in the ceiling on the opposite side of the room. The air moves through the duct in the ceiling space, drawn by a fan, circulating into, and warming the next room.

Heat shifters can distribute heat to other rooms

 

Solar air heaters and heat recovery

Solar air heating systems take warm air from inside the roof space, or from air warmed by passing through glass plate panels exposed to the sun, and push it into the living spaces. Thermostats can control the required indoor temperature. Additional benefits include creating a positive pressure in the house which can reduce draughts and increase thermal comfort. These heating systems rely on efficient electric fans with low running costs; some models use solar powered fans, which may deliver limited air flow.

Heat recovery systems recover waste heat from exhaust air vented from the house and use it to warm fresh input air. The systems do not necessarily add heat to the house but recover the energy lost by venting warmed air, and reduce the amount of energy needed to heat the incoming air.

Cooling options

Cooling options can move the air to directly cool people, or can refrigerate the air to help cool spaces. Options that move the air (fans) are usually space coolers, options that refrigerate the air can be central or space coolers.

Refer to Passive cooling for ideas on making your home cooler.

Top angle view of a living area and kitchen, with a ceiling fan and large sliding glass doors leading to an outdoor area.

This home uses passive cooling strategies when available and makes use of mechanical cooling systems during extremely hot periods

Photo: Simon Wood Photography

Fans

Fans do not cool the air or reduce humidity, but they do provide air movement which helps us feel cool. Fans should be the first appliance of choice for cooling. They are cheap to run and generally use less energy than evaporative coolers or air-conditioners. Typically, the air flow created by a fan provides a similar improvement to comfort as reducing the temperature by around 3°C. With good design and insulation, fans can often supply adequate cooling for acclimatised residents in all Australian climates.

Choose a ceiling fan that has summer and winter settings. Under summer settings, fans force air downward to maximise direct airflow over occupants, delivering the best wind chill effect. Under winter settings, ceiling fans draw cool air upward, gently forcing warm air downward towards occupants, but with a minimal wind chill effect.

Consider ceiling fans with DC motors as they use about 30 watts, or half the energy of a traditional fan and are generally quieter and more compact.

Fans should be sized appropriately to their purpose. For example, you can purchase 5 watt desktop fans connected to your computer for personal cooling. Or you can buy 75 watt fans that can improve the comfort of all occupants in a room.

Tip

You can combine fans with an air cooling system (for example, reverse cycle air-conditioner) to increase the cooling effect and reduce the energy used for cooling.

This means you can get the same comfort at higher thermostat settings (ideally 25 to 27°C in summer), which reduces the energy used for cooling. The savings from reduced running times for air-conditioners more than offsets the cost of fan use.

A simple line drawing of a floor fan, a table fan and a ceiling fan.

Fans come in many sizes and forms; they can be portable (table or floor) or fixed (ceiling)

 

Evaporative coolers

Evaporative coolers use evaporation of water as the cooling mechanism and work best in climates with low humidity.

Evaporative coolers cool outside air and blow it into the house; some windows or doors will need to be left open when the cooler is in use to allow indoor air to pass through. Evaporative coolers bring large volumes of outside air into the house, so when outside air quality is low it may be necessary to limit their use (for example, during bushfires).

Evaporative coolers can be built in to the roof or a window frame, or can be a portable unit. Smaller and older units do not use a thermostat, just a fan speed control. Newer, whole-house systems can be fitted with electronic thermostats and timers.

The purchase cost of systems can be moderate, but operating costs can be low because only the system fan and a small water pump use energy. However, many units have inefficient or large fans and fan motors that can consume significant amounts of energy. Some modern evaporative coolers use far less energy than older models: check with manufacturers.

Evaporative systems can use significant amounts of water. Portable units have to be topped up with water at a rate of about 4L/hr. For central systems, water use can be 25L or more per hour on hot, dry days and this may have implications during water restrictions. Check with your council to see if there are any restrictions on using water for evaporative cooling.

Built-in evaporative coolers can increase heating bills because large volumes of air can be sucked out of the house through the evaporative unit. Many modern units have automatic seals when not in use. Otherwise, close off ducts and cover the roof unit in winter to reduce heat losses.

A diagram of an evaporative cooling unit shows how hot dry air from outside is drawn into the unit through a filter. The filter is kept wet by circulating water which is pumped up from the bottom of the unit before it drips onto the filter. The now cool humid air is blown out the opposite side of the unit by a fan.

How an evaporative cooler operates

 

Air-conditioners

Air-conditioners are available as portable, wall, window, split, multi-head, or ducted systems. Fixed systems need to be installed by a licensed refrigeration mechanic or electrician.

Purchase costs vary depending on the size and type of air conditioner, and efficiency varies widely between units and models. Choose a high efficiency model of the correct size. Systems using inverter technology and advanced design can show energy savings of up to 40% over standard units. You may also consider the type of refrigerant used in your air-conditioner – the majority of new split systems are charged with a refrigerant (Hydrofluorocarbon; HFC-32) that has lower global warming potential (noting that those units are also generally more energy efficient).

Air-conditioners have an energy rating label which tells you how efficient the appliance is, relative to other models of the same size. The zoned energy rating label gives an efficiency rating for different seasons for 3 Australian climate zones, so you can see how the appliance will perform in your region. For more information refer to the Energy Rating website. Air-conditioners also have to meet Minimum Energy Performance Standards, set by the Australian Government.

Ensure your air-conditioner is correctly sized. You can use the Australian Institute of Refrigeration, Air conditioning and Heating’s online calculator or get quotes from air-conditioning installers to ensure you are getting a system that is correctly sized for your space. A technician who holds a Refrigerant Handling Licence needs to install the air conditioner, and can offer advice on the right sized appliance.

For efficient air-conditioning, the house or room should be well sealed and highly insulated with bulk and reflective insulation. The outdoor compressor, as well as your windows, should be shaded from direct sun.

Example of a zoned energy rating label for an air-conditioner.

The zoned energy rating label helps you to decide on the most efficient air-conditioner based on the climate where you live

Source: https://www.energyrating.gov.au/

Some air-conditioners are ‘demand response enabled’. This gives customers with smart meters the option to let their energy provider manage the air-conditioner remotely during times of peak electricity demand, in return for price incentives or other benefits. For more information refer to Connected home.

The available modes of these units will be indicated on the energy label:

  • Mode 1 – the air-conditioner can respond by switching the compressor off for a period (but leave the fans running, so air continues to circulate). This is normally used only in emergencies, when the grid is at risk of blackout.
  • Mode 2 – the air-conditioner continues to cool, but limits its power demand to 50% of its rated capacity. This is more likely to be used during periods when generation costs are high, and to relieve stress on the grid.
  • Mode 3 – the air-conditioner continues to cool, but limits its power demand to 75% of its rated capacity.

Example of an energy rating label sticker which shows two arches. One arch is blue for cooling which shows 6 stars. One arch is red for heating which shows 6 stars. Below each arch there is a reference to the power consumption for that appliance.

Energy rating label for a demand-response capable air-conditioner

Source: https://www.energyrating.gov.au/

Portable air-conditioners

Portable air-conditioners may be single duct units on rollers, or window units. They are suitable for single rooms up to about 50m2 but are less efficient than fixed split systems, resulting in higher energy usage and running costs. The units draw air from other rooms in the house as they vent air, typically heating them up, and they do not work well in large rooms.

Portable single duct units consist of a single indoor unit which can be on rollers and a duct to release the hot condenser air outside, usually through a window. The outlet often does not seal tightly and heat can enter the room.

Window or through-wall units are placed in an existing external window or a hole made in an external wall. Smaller units can use a standard electricity outlet, but larger ones may need a dedicated electrical circuit installed.

A portable free-standing air-conditioning unit is plugged into a wall power socket and a flexible plastic tubing duct connected to the unit passes through the same wall.

Portable air conditioners are less efficient than fixed systems

Photo: Paul Ryan

Fixed split systems

In a fixed split system, an outdoor unit has a compressor and condenser, and an indoor unit has the evaporator coil and fan. Split systems may also provide heating.

Fixed split systems, especially those using inverter technology, are the most efficient domestic air-conditioners. The indoor unit can be mounted on the wall or floor, and can be located up to 15m from the outdoor compressor. Multi-split systems have more than 1 indoor unit running off the (larger) outdoor compressor.

A simple diagram of a house shows an outdoor compressor unit outside the right side of the house. Cables pass under the floor of the house and into an indoor wall mounted unit in the room on the left side of the house.

A split system unit can be located away from the outdoor compressor

 

Ducted air-conditioners

In a ducted air-conditioner, an outdoor unit has a compressor and condenser, and the fancoil is situated in the roof. Ducts then pump cool air from this central point throughout the home. Ducted systems may also provide heating. Refer to Reverse cycle air-conditioners in this chapter for more information.

Ducted air-conditioning units cool large areas or an entire house. Ducts must be well insulated, to at least R1.5, and joints sealed to prevent condensation and leakage. The roof should have reflective foil insulation installed and be vented to dispel hot air. Zone systems cool only occupied areas and allow different conditioning in living and sleeping areas.

A simple diagram of a house shows an outdoor compressor unit outside the left side of the house. Cables pass through the ceiling space of the house and into a unit in the ceiling. Ducts from the ceiling unit open through the ceiling into three different rooms of the house. Openings in the internal walls allow the cool air to circulate.

Ducted units can cool an entire house

 

Solar air cooling

Solar air cooling systems use a fan or ventilator to extract hot air out of the roof space or the gap between the sarking and metal roof sheets. By extracting hot air from the roof space and replacing it with ambient air, it minimises heat transfer to the ceiling space below.

The effectiveness of removing hot air from the roof space is affected by the roof colour and presence of reflective foil under the roofing. A dark (or unpainted steel) roof absorbs a large amount of heat. The temperature in the roof cavity is significantly reduced only by a large air flow, well beyond the capacity of most fans and vents. A light roof or reflective foil under the roofing dramatically reduces heat gain, so ventilation systems are more likely to make a noticeable difference.

Systems using a solar panel as the only source of electricity have no running costs, but work only in sunny conditions. Some systems combine daytime and night-time cooling. The advantage of a system using grid electricity to power the fan is that night-time cooling can flush heat out of the building overnight.

Using heating and cooling

You can reduce your heating and cooling costs by the way you use your heating and cooling, and by making minor changes to your home.

Tips for heating and cooling your home

  • Each degree of extra heating in winter or cooling in summer increases energy consumption by about 5–10%. Set the thermostat to 18 to 20°C in winter and 25 to 27°C in summer.
  • Locate thermostats in the most used rooms and away from sources of heat and cold.
  • Heat and cool only the rooms or spaces you use most and close doors to other areas.
  • Close windows and doors in areas where a heater or air-conditioner is on, unless ventilation is required for unflued gas appliances or evaporative cooling.
  • Close drapes or blinds, especially during the hottest part of the day in summer and in the evening in winter.
  • Block gaps around doors or windows with a draught stopper or sealant.
  • Do not leave heating and cooling appliances on overnight or when you are out. If you must have the house comfortable when you arrive home, install a timer and turn your system on about 15 minutes before your return.
  • Service all heaters and coolers according to the manufacturer’s instructions. Pay special attention to cleaning air filters.

Tips for feeling warmer or cooler

Many people focus only on changing the temperature of spaces in their homes to feel comfortable. But whether or not you feel comfortable in the climate within your home depends on many factors. These include:

  • air temperature
  • humidity
  • air movement
  • temperature distribution
  • temperature of surfaces in your home
  • materials in your home (for example, tiles, carpet, etc)

Paying attention to all of these factors can reduce the amount of heating or cooling required at minimal cost. This approach can help you to save energy and money in the long term.

Feeling warmer

  • Wear warm clothing – When you feel cold, it means you are losing body heat. The most efficient way to prevent this is to wear warm clothing that covers as much skin as possible. Keep your feet warm by wearing slippers or socks, or by placing rugs over cold floors. Our feet are particularly sensitive to temperature. Bare feet on cold floors can make you feel cold and uncomfortable, even if the rest of your body is warm.
  • Prevent draughts – Cold air feels even colder when it is moving. Cold air falling off windows and outside air entering your house can produce draughts that make us feel cold. Placing draught stoppers under doors and heavy curtains over windows can prevent draughts.
  • Position your heater and furniture strategically – Uneven temperature distribution makes us uncomfortable. If you are seated between a cold area (for example, a single-glazed window) and a heater you will likely feel cold on one side and may feel the need to turn the heater on a high setting. In addition, all heaters produce air movement and can actually cause draughts. When air is heated, it rises to the ceiling. It then cools and falls when it comes into contact with cold surfaces such as windows, and falls to the floor where it is drawn towards the heater again. Even if the air in a room is generally warm, draughts can make us feel cold. Place heaters to avoid draughts, and place seats and lounges away from the path of returning air.

A diagram of a living room and lounge area shows the movement of warm air from a heater, as it rises and is lost through a window on the opposite side of the room. Cool air shown as a draught, seeps into the home through the same window.

Draught caused by placement of heater and heat loss through window

Source: Joe Wyndham

Feeling cooler

  • Wear cool clothing – Our bodies have a built-in cooling system. When we feel hot, we produce sweat, which evaporates, carrying heat away from or bodies. By wearing short-sleeved, loose-fitting, breathable clothing we allow this process to occur unimpeded.
  • Improve air movement by opening windows and doors – Air movement increases the evaporation of sweat and this helps us feel cooler, particularly in humid weather. To increase the air movement in our homes, it is generally best to create a cross-breeze by opening doors and windows on opposite sides of the building. This approach should not be used in conjunction with standard air-conditioning as you do not want to lose air that has been cooled. Evaporative coolers do rely on some windows and doors being open to allow large volumes of air to pass through the house.
  • Shade your home – Shades and blinds, particularly those that are external, can help block sunlight and prevent your house from getting hot during the day. Ensuring that shades and blinds are positioned to block sunlight, especially in the heat of the day, will keep your home cooler and more comfortable. You can also plant deciduous trees or shrubs to provide shade in summer and let sun through in winter.

References and additional reading

Learn more

  • Read Passive heating and Passive cooling for tips on how to reduce your need for heating and cooling.
  • Look at Renovations and additions for more ideas on how to update your home to be more energy efficient.
  • Explore Shading to find out how to use shading elements to let sun into your home in winter and block it in summer.

Authors

Original authors: Geoff Milne, Chris Reardon

Contributing authors: Paul Ryan, Murray Pavia

Updated: Joseph Wyndham 2020