Energy

Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.

Space heating – energy sources

Comfort, health, efficiency and environmental issues all influence decisions about the right energy source to use for space heating.

On this page:

  • Efficiency of commonly used heating options
  • Electric heaters
  • Heat pumps
  • Gas heaters
  • Solid fuel burners
  • Oil burners
  • Solar heating

The best option for space heating is – of course – the sun. By siting and orienting a building to take advantage of solar gain, and using insulation and thermal mass to capture and store heat, it may be possible to significantly reduce the amount of additional heating required to maintain comfortable temperatures. (See passive design for detail.)

But, even with effective passive solar heating, most New Zealand houses will also require top-up heating at times – especially during the cooler months of the year. The most common sources of energy for space heating in New Zealand homes are electricity, wood (either in open fires or in wood burners), and gas.

Other options include solar hydronic heating, and heat pumps. In recent years, there has been rapid uptake of heat pumps and these are now common in both new and existing houses.

When specifying a heating source, consider:

  • its suitability for the purpose – Are you trying to provide short-term heating for a single person (such as in a bathroom), or to maintain comfortable temperatures for several room occupants over reasonably long periods (such as in a living room)? This will determine whether you choose radiant or convective heating, as well as the heater size and control systems (e.g. thermostat or manually controlled). By specifying the heater that is most suitable for the purpose, you can maintain occupants’ comfort and health while reducing energy use. See space heating options by room for more.
  • the environmental impact of the fuel used – Does the fuel emit moisture, carbon dioxide and other greenhouse gases? Ministry for the Environment figures show that 58% of human-made airborne particles in 2013 were from burning wood and coal for home heating. Are there other environmental impacts from its extraction or manufacture? How efficient is it at converting energy to heat?
  • the health impacts of the fuel used – Is it ‘clean’ or does it emit moisture or gases that might affect occupants’ health?

The aim, in essence, is to maximise occupants’ comfort and health, while minimising harmful environmental impacts.

Efficiency of commonly used heating options

While portable electric or gas heaters are convenient and relatively common, they are often not the most efficient option.

The different space heating options available can be categorised according to their efficiency or Coefficient of Performance (COP). The COP is the ratio of energy input to energy output. A COP greater than 1 means that the heating method produces more energy (in the form of heat to warm a building and its occupants) than it consumes; a COP less than 1 means that the heating method consumes more energy than it produces.

Best efficiency
(COP >1)
Good efficiency
(COP about 1)
Average efficiency
(COP <1)
• Solar energy (good passive design, appropriate glazing etc.) for entire space heating needs.
• Heat pumps (convective heat).
• Electric heating – radiant or convective.
• Hot water heating – radiators connected to an electric boiler.
• Underfloor (electric cable) radiant electric heating.
• Flued natural gas, or LPG – convective or radiant.
• Underfloor hydronic (hot water) radiant heating – gas, electric or heat exchange.
• Hot water heating (radiator) – gas or oil.
• Ducted hot air from electric, oil, gas or LPG.
• Solid fuel burner.

Electric heaters

Electricity provides energy for portable and fixed convective heaters, radiant panels and bar heaters, bathroom light heaters, oil-filled column heaters, heat pumps, nightstore heaters and embedded floor heating cables. Electricity may also be used to heat water for hot water radiator central heating and embedded hydronic floor heating systems, and to heat air in ducted central heating systems.

Electric heating converts 100% of the energy used to heat. When fan assisted, it also distributes heat efficiently.

Advantages of electric space heating include that:

  • electricity is readily available
  • there are no emissions in the home
  • output is controllable – either thermostatically or by timer
  • heat can be targeted with portable and free-standing units
  • electric heaters are convenient and easy to use
  • most electric heaters have low initial costs
  • electric heaters are low maintenance
  • electric heating may be powered using a renewable source such as hydro or wind (about 75% of New Zealand’s electricity generation is from renewable sources)
  • efficiencies range from 100% (radiant heater) to over 500% (some heat pumps).

Disadvantages include that:

  • electric heaters may be costly to run, and costs will continue to rise as electricity prices rise
  • electricity generation can have negative environmental impacts, such as greenhouse gas emissions from burning gas, coal and diesel to generate electricity, damming of rivers and visual impact and noise pollution from wind farms.

Heat pumps

Air-to-air heat pumps use refrigerant to absorb heat from outside a building and transfer it inside, via a heat exchanger. Heat pumps use electricity to move heat around, but not to generate it.

The key advantage of heat pumps are their high efficiency at converting energy to heat. A heat pump will provide the same amount of heating with much lower energy input than a standard electric or gas heater.

Heat pumps are also responsive – providing heat relatively quickly when it is needed.

They can provide cooling as well as heating, which is an advantage in terms of thermal comfort but can be a drawback in terms of environmental performance; as heat pumps have become more common, summer electricity demand has tended to increase, offsetting the gains made from more efficient winter heating.

Another disadvantage is relatively high up-front costs. Heat pumps are, nonetheless, a highly efficient method of space heating.

Ground source heat pumps (sometimes called geothermal heat pumps) are also available in New Zealand. These use a network of pipes underground beyond the building envelope to collect heat. Some have a bore so pipes go deep into the earth, taking up less surface space. They typically provide heat for underfloor home heating systems, but can also provide a heating source for hot water supply and even a swimming pool. Their initial costs are high, but they have good efficiency even when outside temperatures are very low. A significant number of these systems in New Zealand are installed in South Island alpine locations.

See heat pumps for more detail.

Solid fuel heating

Solid fuels for heating include wood pellets, wood, and coal. They may be used for direct heating of spaces or to heat water for hot water heating systems. Wood in particular is a popular option – the 2013 census found that 36% of New Zealand households use wood to heat their homes.

The National Environmental Standards for Air Quality require that all wood burners installed on properties less than 2 hectares must have:

  • a discharge of less than 1.5 grams of particulate for each kilogram of dry wood burnt
  • a thermal efficiency of at least 65%.

The Ministry for the Environment website has a list of authorised wood burners and pellet burners that have been tested and found to meet the performance requirements. Regional councils can apply rules that are more stringent than the National Environment Standards in their area. All new woodburner installations require a building consent.

Open fires and multi-fuel burners designed to burn wood and/or coal are not covered by the National Environmental Standards, but a number of regional councils have imposed rules or restrictions around them in their region.

For solid fuel consumed within a closed firebox burner, around 55–80% of the energy from the fuel is converted into heat, compared with open fires, where around 15–30% of the energy is converted into heat (although manufacturers of a steel firebox that can be retrofitted into open fireplaces claim an efficiency of up to 50% for their product). In many parts of New Zealand, open fires are no longer permitted.

Advantages of solid fuel heating include:

  • the aesthetics of a flame
  • they can provide high heat output
  • they may be able provide water heating (e.g. wetbacks)
  • many people have access to free or cheap firewood.

Drawbacks can include:

  • byproducts of combustion must be vented outside
  • depending on the fuel used, toxic emissions and smoke may be released into the atmosphere
  • a source of (cheap) wood is not always available
  • control over heat output rate and therefore temperature is limited
  • it may be difficult to achieve efficient heat distribution from a single source
  • maintenance is required (ash removal, cleaning of flues and dirty heating surfaces)
  • they may cause staining within the room (particularly from open fires).

Different types of solid fuels and solid fuel heaters vary widely in their environmental impact. Enclosed woodburners generally burn more efficiently and produce fewer emissions than open fires.

Pellet burners are similar to wood burners but, instead of burning timber, they burn pellets that are manufactured from waste wood shavings and sawdust. They tend to produce fewer emissions than enclosed wood burners. They require electricity to control a thermostat that, in turn, controls the supply of pellets to the fire box, so in the event of a power supply cut, the pellet burner will not operate.

 

Gas heaters

Gas can be used as an energy source for a number of heating options including radiant and convective in-room heaters, ducted hot air systems and for heating water for hot water heating systems.

Advantages of gas heating include:

  • approximately 80% of the energy used is converted into heat
  • radiant heaters can provide the aesthetics of an open flame
  • gas heaters can provide high heat output relatively quickly
  • gas convective heaters can be thermostatically controlled (with radiant units, it is only possible to control heat output).

Disadvantages include:

  • burning fossil fuels
  • byproducts of combustion must be vented to outside
  • reticulated gas may not be available
  • initial installation costs are higher than for electricity
  • there may be issues with security of supply for gas in the future.

For health and safety reasons, BRANZ does not recommend the use of any sort of unflued gas heater (natural gas or LPG).

Oil heaters

Oil has been a popular bulk fuel for domestic heating systems in the past. A small number of oil-fired heating appliances are still available.

Disadvantages of using oil as a fuel include:

  • burning fossil fuels
  • the possibility of limited supply in the future
  • cost
  • potential hazards from spills
  • flue emissions.

Solar heating

Solar heaters use solar radiation to heat:

  • water that circulates through radiators, or
  • an air supply coil, or
  • air, for direct supply to internal spaces.

Solar heating is highly efficient, as energy is generally only consumed to operate a water pump, refrigerant pump, or air fan.

However, for some forms of solar heating, the heat capacity can vary, and heat is only available when the sun is out – not necessarily when heating is needed.

More information

 

Updated: 15 February 2017