Heating and cooling | YourHome

Very little energy is needed to make a well-designed house comfortable. Appropriate insulation, which is essential for a comfortable house, combined with passive solar design and a draught-proofed building, can create low or even no energy requirements for heating and cooling (see Passive solar heating; Insulation). Highly efficient homes with no heating or cooling input are possible across much of Australia.

Even for existing homes there are many ways to reduce energy bills, improve comfort and help the environment. The principles of thermal comfort and the importance of air movement, humidity and radiant heat are explained in the section Passive design.

Projected average home energy use in 2012 actual energy use varies from state to state (particularly with climate) and from home to home depending on the heating and cooling systems in the home and how they are used.

Household energy use

%

Source: DEWHA. 2008

Heating and cooling

40

Water heating

21

Appliances and equipment including refrigeration and cooking

33

Lighting

6

Never use mechanical heating and cooling as a substitute for good design. However, for existing homes, installation of high efficiency heating and cooling technologies, with modest building improvements and behaviour change, may be cheaper options to reduce energy bills and greenhouse gas emissions than major home renovations.

Your money is better invested in an energy efficient building than spent on heating and cooling.

At 40% of household energy use, heating and cooling are together the largest energy user in the average Australian home (DEWHA 2008). However, since most home heating uses gas, heating is responsible for a lower proportion of energy bills and greenhouse gas emissions than its share of energy use suggests.

Use passive design principles to increase comfort and reduce the need for heating. Insulate the roof, walls and floor, seal off draughts, let in winter sun and draw curtains at night. Zone your existing or new home and only heat the rooms you are using; use doors to prevent heat escaping into unused rooms (see Passive design).

The two main types 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.

Other forms of heating, such as heated floors, also heat by conduction through direct contact.

Different forms of heating are best in different circumstances:

Heaters produce air movement as hot air rises and then falls as it cools.

All heaters produce air movement as the hot air rises from the heater to the ceiling. Air is cooled when in contact with windows and poorly insulated walls and ceilings. The cooled air falls and is drawn back along the floor to the heater.

Sitting in draughts created by air movement can make you feel much colder. Minimise draughts from windows and use heavy curtains with snug pelmets or other ways of preventing air flow through gaps at the top and sides of window coverings to stop convection and radiant heat loss. Always consider appropriate clothing to stay warm and reduce the effects of draughts. Position your furniture to deflect or avoid draughts.

Position your heater and furniture to deflect and avoid draughts.

Choosing a correctly sized heater (and cooler) is very important. Do not install an oversized heater, as you will be wasting money on buying a bigger heater than you need and wasting energy/money in operating it. Expert advice helps make sure you are choosing a correctly sized heater.

An oversized heater wastes money and energy.

Gas heaters and efficient reverse cycle air conditioners (or heat pumps) produce only one-third the greenhouse gas emissions of standard electric heaters. The most efficient 56 star reverse cycle units actually produce less than one-fifth of the emissions of conventional electric heaters.

Gas heaters and reverse cycle air conditioners have Energy Rating Labels to help you choose the most efficient model.

Wood can be an excellent fuel because it is a renewable resource if sustainably harvested. However, do not use wood fired heaters in urban areas because of the air pollution they create, and the emissions associated with transporting firewood to urban areas.

About 10% of homes use wood for heating but the wood is often obtained from unsustainable sources. Use only sustainably harvested wood to avoid habitat destruction and rare species extinction.

Do not use treated timbers, which may give off toxic pollutants when burned.

Burn wood only in airtight, slow combustion heaters. They have the highest energy efficiency of wood heaters, and use the least wood and cost the least to run. Careful operation of wood heaters is also critical to limiting air pollution. Use seasoned wood and dont add large loads of wood just before turning the heater right down. Do not use illegally modified heaters, adjusted to burn overnight.

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:

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 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.

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 feetwarm 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.

Hydronic systems circulate hot water or coolant through radiator panels in rooms, supplying a mix of convective and radiant heat.

Hydronic systems are usually gas fired but can be heated by a wood fired heater, solar system or heat pump. Solar systems can use gas or wood heating as a back-up. These systems have the advantage of adaptability to energy sources as energy markets change.

Each panel or room should have its own control.

Low water content systems are best as they reduce energy use. Ensure water circulation pipes are well insulated, and smart controls 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 loss to the outside. Use wall cavity insulation or a layer of installed reflective foil on the internal wall behind the panel. Ideally all exterior walls should be insulated to maximise comfort from the heating system, especially in a new home or major renovation.

Concrete floors can be used to store heat from off-peak electric cables or hydronic pipes set into the slab. They are installed during building construction or renovation. (see Concrete slab floors)

Slab insulation is very important, so that heat from the slab does not leak into nearby cold, wet earth. Insulate slab edges, and ideally the entire slab, from the ground to minimise heat loss. Insulate walls from the slab to reduce heat loss.

Electric in-slab heating generally has the highest greenhouse gas emissions of any heating system. As electricity prices have increased, in-slab heating costs have also increased.

The best in-floor system for minimising greenhouse gas emissions is a hydronic system using one of the following:

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 only needed occasionally and in changeable weather. They are ideal as back-up for passive solar heating of thermal mass on cloudy or extremely cold days but use caution if you heat the slab then the ability to store heat from passive solar gain is reduced.

Avoid heating areas of the slab exposed to the sun in winter.

Heating zones and thermostats are essential to reduce energy use. Slab heating running costs are particularly sensitive to air leakage through gaps.

The central heating comparison table assumes well designed and efficiently operated systems and gives general running costs and greenhouse gas emissions. Obtain expert advice before making decisions on the type best for you.

System type

Running cost

Greenhouse gas emissions

High efficiency ducted natural gas

Low

Low

Hydronic zoned natural gas or heat pump

Low

Low

Ducted reverse cycle or heat pump

Medium

Medium (low with green/renewable electricity source)

Hydronic zoned with wood/solar heat source

Low

Very low (if from a renewable resource and seasoned wood)

In-slab high off-peak electric

Mediumhigh

Very high (low with green/renewable electricity source)

These devices heat a smaller area one or perhaps two rooms and come in a wide range of types.

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

Heaters that dont rely on fans and do not 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.

Electric systems may produce high greenhouse gas emissions up to six times as much as an efficient gas heater. However, using a small electric heater for local heating may be cheaper and have lower emissions than heating a much larger area with gas. Offset electricity greenhouse emissions by using 100% GreenPower.

Offset electricity greenhouse emissions by using 100% GreenPower.

Reverse cycle air conditioning (or heat pumps) provides convective heat and is the most energy efficient electric heater. The most efficient 56 star units may be cheaper to run and generate lower greenhouse gas emissions than gas heaters. Visit the Energy Rating website (www.energyrating.gov.au) to find the most efficient reverse cycle air conditioners.

Wall panel convectors use peak electricity and are expensive to run, like portable electric heaters.

Off-peak electric storage heaters provide a mix of radiant and convective heat. They use bricks to store heat produced overnight using off-peak electricity. Unless carefully controlled they can lead to overheating in milder weather, and they continuously leak heat, so their overall efficiency in intermittently used spaces is low.

Unflued portable heaters can provide either convective or radiant heat and run on natural gas or LPG.

Adequate ventilation is needed to maintain good air quality, which can significantly reduce efficiency. An efficient externally flued heater is usually preferable but may not always be an option, particularly for tenants. In these cases units are available that burn more cleanly, producing lower combustion emissions and requiring less ventilation.

Unflued gas heaters often create condensation problems usually at the opposite (coolest) end of the house. Take care to ensure they dont lead to mould growth.

The use of unflued heaters is restricted in some states because of their associated indoor air pollution hazard, which can cause health problems. Check your state or territory regulations for details.

Wall units and floor consoles can provide convective and/or radiant heat, and usually have fans to circulate hot air. Most are flued, requiring less ventilation and producing fewer condensation problems.

Gas fixed heaters usually have fans to circulate hot air.

Some fixed gas heaters use fan-powered flues or balanced flues: they draw in outdoor air, heat it, then return it outdoors. Other gas heaters use indoor air for combustion, and rely on flues to remove the waste gases from the house. In well-sealed houses, there is a risk that exhaust gases can be drawn back into the house through exhaust fans, such as kitchen range hoods or bathroom exhaust fans, creating health and safety risks.

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Heating and cooling | YourHome