Energy

Common options for energy sources to heat New Zealand homes include:

• electricity
• solid fuel
• gas
• oil.

Heaters using these fuels are popular because they’re familiar, readily available and relatively simple to install and operate. However, houses where these are the main option are less energy-efficient and sustainable than those that use some form of passive heating.

Electricity

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
• they are convenient and easy to use
• they have low initial costs (except for heat pumps)
• they are low maintenance
• they can be powered using renewable electricity generation.

Disadvantages include that:

• they 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 oil and coal to generate electricity, damming of rivers and visual impact and noise pollution from wind farms.

Solid fuel

Solid fuels for heating include pellets, wood or coal. They may be used for direct heating of spaces or to heat water for hot water heating systems.
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 5–15% of the energy is converted into heat. Note: Open fires are no longer permitted in many parts of New Zealand.

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
• 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
• may be difficult to achieve efficient heat distribution from a single source
• maintenance is required (ash removal, cleaning of flues and dirty heating surfaces)
• 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. However, 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.

Heaters burning wood and coal produce toxic emissions and smoke that create smog and can cause respiratory disease. All woodburner installations require a building consent and should comply with National Environmental Standards (mandatory on building sites of 2 hectares or less).

Gas

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
• they can provide high heat output relatively quickly
• convective heaters can be thermostatically controlled (control of heat output only with radiant units).

Disadvantages include:

• 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.

BRANZ does not recommend the use of any sort of unflued gas heater (natural gas or LPG).

Oil

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.

Passive heating

Passive heating systems include:

• passive solar gain, which utilises the position and orientation of the house to take advantage of daytime solar heat gain, combined with high levels of insulation and thermal mass for heat storage, and can limit the requirement for additional heating
• solar heaters, which use solar radiation to heat water that circulates through radiators, heat an air supply coil or directly heat air for supply to internal spaces.

Passive energy sources are efficient utilisers of energy. The energy consumption is generally only to operate a water pump, refrigerant pump or an air fan.

However, for some forms of passive energy heat capacity can vary, and heat is only available when the environment conditions are appropriate (for example, during daylight hours for solar) – not necessarily when heating is needed.

More information

• www.smarterhomes.org.nz/energy/heating