Energy

Most New Zealand homes are heated by consuming bought energy such as electricity, gas, and solid fuels. 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 designed for optimal warming by the sun, or those which make use of recovered heat sources.

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, embedded floor heating cables and heat recovery ventilation systems. 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 space heaters convert 100% of the energy used to heat. In general, they are also efficient at distributing heat when fan assisted.

The advantages of specifying electric space heating are that:

• electricity is readily available
• there are no emissions in the home
• output is controllable – either thermostatically or by timer
• they can be portable and free-standing, so heat can be targeted to where it’s needed
• they are convenient and easy to use
• they have low initial costs
• they are low maintenance
• they can be powered using renewable electricity generation.

A key disadvantage is that electric space heaters can be costly to run and they will become more expensive to run as electricity prices rise. Electricity generation can have negative environmental impacts, including:

• greenhouse gas emissions from burning oil and coal for generation
• damming of rivers
• visual impacts and noise pollution from wind farms.

Solid fuel

Solid fuels for heating are pellets, wood or coal. Solid fuel can be used to directly heat the space or as a boost to hot water heating systems.

For solid fuels consumed within a closed fire box burner, about 55-80 % of energy used is converted into heat. For traditional open fires, about 5-15% of energy used is turned into heat.

Advantages of solid fuel heaters include:

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

Drawbacks can include:

• staining within the room (particularly with open fires)
• by-products 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
• it’s not always possible to achieve efficient heat distribution from a single source
• maintenance is required – i.e. cleaning of flues and dirty heating surfaces.

The different types of solid fuels and solid fuel heaters vary widely in their environmental impact. Woodburners are generally better than open fires, for example, and there is some evidence that pellet burners are better again.

Heaters that burn wood and coal produce toxic emissions and smoke that can cause smog and respiratory disease. Open fires have been banned by many cities and local councils. 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 specified as an energy source for a number of heating options. Gas can be used as the fuel for radiant and convective in-room heaters, ducted hot air systems, and to heat the water for hot water systems.

Advantages of gas heaters include:

• approximately 80% of the energy used is turned into heat
• for radiant heaters people like the aesthetics of a flame
• they can provide high heat output relatively quickly
• convective heaters can be thermostatically controlled (heat output control only on radiant units).

Disadvantages include:

• by-products of combustion should be vented outside
• reticulated gas may not be available (may have to rely on gas cylinders for supply)
• moisture is produced when gas is burnt in unflued heaters
• initial installation costs are higher than for electricity
• longer term, there may be issues with security of supply for gas.

Oil

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

Drawbacks of specifying oil as a fuel include:

• fossil fuel usage and the possibility of limited supply in the future
• cost
• potential hazards from spills
• flue emissions.

Passive energy for heating

Passive heating systems include:

• solar heaters  – these use solar radiation to heat water that runs through room radiators, or heat an air supply coil, or directly heat air for supply
• heat pumps – these use the temperature of a warm mass such as outside air or water to heat refrigerant which transfers heat to an indoor heating coil

Passive energy sources are very efficient at converting energy to heat. In most cases, the only energy consumption is to drive a water pump, refrigerant pump or an air fan.

When adopting passive energy for space heating:

• heat is only available when the environment conditions are appropriate (for example, during daylight hours for solar) – not necessarily when heating is needed
• heat capacity can vary.

For your clients

To help your clients make decisions about space heating options, refer them to www.smarterhomes.org.nz/energy/heating.