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5 Discussion

This review covers printed and on-line material relating to the use and performance of domestic home heating appliances in use in New Zealand. It aims to include any material that classifies and objectively assesses appliances by type, within the following categories:

  • appliance energy efficiency by type of appliance
  • appliance costs - capital and operating
  • extent of ownership of appliances
  • typical use of appliance: hours per day, days per year
  • adverse effects of use
  • beneficial effects of use
  • ease of operation
  • availability of fuel supplies
  • regulations pertaining to heating appliances.

This review does not include promotional material from manufacturers, although this is readily available for appliances currently on the market.

Note that:

  • heating appliance emission figures are sourced from Scott (2004), Gas Appliance Suppliers Association Inc (2004) and Environment Canterbury (2004b)
  • heating appliance capacity and capital cost figures are sourced from Ward (2004), MfE (2002) and the authors' own experience
  • all own calculations are based on information from Baines (1993); gas and electricity prices were obtained from published tariffs accessed on 10 December 2004
  • wood prices were obtained from retailers.

It is also assumed that:

  • appliance classifications are consistent among reports
  • figures provided by fuel suppliers are accurate and have been interpreted correctly by the authors.

At the end of Appendix 2 there are two graphs showing a presentation of the costs of operating various heating options. The first graph includes open fires amongst the appliances presented. The second graph excludes open fires which, with their relatively high operating costs, tend to make comparisons between the other options less clear.

Appliance energy efficiency, by type of appliance

A comparison of the efficiency of a number of types of heating is provided in MfE (2002). This information forms part of a technical report written to inform decision-making relating to reducing emissions from domestic home heating. Where appropriate, this work examines a range of types of heating appliance for each energy source (eg, electricity, gas and wood). This document references a number of related bodies of work offering further data. Efficiency figures are consistent with generally accepted values.

The work of Ward (2002) also examines a range of heating options for each fuel source. It provides the reader with sufficient information and guidance to enable potential suitable types of heating to be identified according to the proposed application.

The Environment Canterbury (2004b) web pages relating to oil and wood burner emissions include appliance efficiency information. This does not provide any information about other types of heater (such as electric), but does serve as a source of information to enable wood or oil burners to be compared.

It is worth noting that the efficiency figures quoted refer to the efficiency with which delivered energy is turned into heat by the heating appliance. These figures ignore energy losses associated with the generation or production of the energy/fuel concerned and the losses due to distributing and transporting the energy/fuel. These losses can be ignored at the household level when comparing the efficiency of the heating appliances, but they should be considered when considering the relative efficiencies of heating types and fuels in terms of their social/ environmental effects.

Appliance costs - capital and operating

MfE (2002) provides an indicative range of capital costs and also develops operating costs for each heating type presented. This work provides an indication of relative cost of operation, although fuel price increases since this document was published have made the absolute values inaccurate. The same is true for the capital costs presented.

Ward (2004) covers a more comprehensive range of appliances than the MfE (2002) report. In general the costs are in agreement, but Ward's material reflects recent fuel price rises and the increasing diversity of appliances. No source material is referenced.

The operating cost figures produced by the Christchurch City Council (Itskovich, 2004) are very generic but are in general agreement with the work of Ward and with the results produced in the course of compiling the current report. Information from Baines (1993) has been used extensively in this report.

Note that the costs presented for all appliance types in section 4 are theoretical and do not take into account occupant behaviour or factors such as house construction and insulation. The work of MfE (2005) is based on measured heating energy consumption, and so provides a way to compare theoretical and actual values. The most recent Building Research Association of New Zealand (BRANZ) Home Energy End-use Project report (BRANZ, 2004) also includes measured fuel consumption figures. Walker J, pers. com. (2004) includes information about the effect of the use of heat pumps on users' electricity bills, but this is largely anecdotal and does not contribute quantitative material.

Operating costs will also vary from region to region and over time. In this document the objective has been to use reasonable and current estimates of the various costs so that comparisons can be made between different heater types. Future phases of this project will include the development of a model that will allow comparisons to be made based on an unlimited number of inputs for capital and operating costs of various appliances.

Although some households using wood as a source of fuel do so by gathering their own wood for 'free', there is usually some cost associated with this fuel gathering; for example, vehicle running costs, trailer or chainsaw hire. For the purposes of this analysis it is assumed that wood used as a fuel is sourced from commercial operators at current market prices.

Extent of ownership of appliances

The BRANZ Home Energy End-use Project has documented the use of appliances for a number of years and has added to this with each new survey round. The most recent report (BRANZ, 2004) provides detailed information about relative numbers of heating appliance types but does not provide an analysis of heater type by region.

MfE (2005) investigates the extent to which different types of appliance are used throughout New Zealand. This research covers seven locations, six of which (Invercargill, Gore, Reefton, Westport, Upper Hutt and Te Kuiti) are not generally included in work of this type. The Environment Canterbury Christchurch Home Heating Survey (Lamb, 2002) investigated the relative numbers of appliance types in use within Christchurch. Finally, the 2001 Census includes information about heating appliances available in houses. While this information is now becoming outdated, it does provide an indication of relative numbers of appliances.

Typical use of appliances: hours per day, days per year

This information is available as part of the Home Energy End-use Project work carried out by BRANZ (2004) to measure residential energy use. This work is concerned with analysing overall household energy use, and it also provides a comparison of use by region. However, it does not provide detailed information about heating use, including seasonal and daily heating use by heating type. The draft work of MfE (2005) builds on this and provides more detailed information about actual use.

Work carried out on behalf of Environment Canterbury (Lamb, 2002) reports the extent of use of heating systems by type, but covers only Christchurch.

These pieces of work were limited in the number of participants they could include in their surveys. As a result, the small sample size has the potential to introduce significant errors if extrapolating to obtain indicative regional or national figures.

Adverse effects of use

The adverse effects of using a heating appliance vary according to the type of appliance, when it is used and how it is operated. The most significant adverse effect is arguably air pollution. Research published in Scott (2004) quantifies this for particulate emissions, trace gases and carbon monoxide for combustion heating appliances fired by coal, wood, pellets, oil and gas. It does not attempt to quantify emissions associated with the generation of electricity. The figures are presented as g/kg with no g/MJ equivalents; the latter format is preferable for some applications because it provides the basis for broader comparisons.

Ministry for the Environment (2002) discusses the benefits of a means of quantifying emissions reliably, but does not provide any information for appliances.

Beneficial effects of use

At any given time, when the use of home heating is required, a wide cross-section of heating types will be in operation. Some of these appliances may cause problems, but in some cases may help to overcome other problems. For example, on a very cold, still night, the emissions from wood burners and coal fires can cause bad air pollution, but can also help to remove load on the electricity transmission and distribution networks, preventing black-outs. There appears to be no published research into how to achieve balance between these conflicting demands.

Ease of operation

The main aim of using heating appliances is to bring a room or house to a desired temperature. It is important that the user of a heater should be able to control the appliance so that the aims can be achieved. Little material is available on this subject except from manufacturers.

The work of Ward (2004) is intended to enable users to identify the most appropriate type of appliance and to understand the operational implications of each. As with running costs, ease of operation varies from user to user. It would be helpful if potential users could be made aware of issues that other users had experienced when operating appliances over a period of time. Walker J, pers. com. (2004) discusses this, but the small sample size and anecdotal responses make this report interesting but not particularly useful.

Availability of fuel supplies

One aspect of the dependability of a heating appliance is the ready availability and affordability of its energy source. Most of the appliances currently on offer use energy sources that are generally in plentiful, but not unlimited, supply. The situation regarding any or all of these energy sources changes on a daily basis as a consequence of global events.

No single definitive publication covers this topic, although there is a wealth of background information on oil, gas and electricity supplies. The most relevant and topical information can be found in the daily press and in business or current affairs periodicals.

Regulations pertaining to heating appliances

The choice of heating appliance is becoming increasingly constrained by local and national emissions regulations. The regulations covering emissions to air in Canterbury are set out in Environment Canterbury, 2004a. MfE (2002) discusses other proposed or current regulations.

The Ministry for the Environment (2004) has set out draft national environmental standards, which will impose restrictions on emissions. There is no reference to other legislation in draft at present, but information of this nature would be beneficial to the current work.

Whole house vs single room heating

It is worth noting that some of the heating options detailed in this report are capable of heating an entire home (eg, central heating systems). Such heating systems are typically priced around, or in excess of, $10,000. Other options are capable of heating a single room only (e.g. smaller heat pumps and unflued gas heaters). These options are typically priced at less than, or around, $2,000. Most solid-fuel burners fit in between these two situations. They are capable of heating more than one room and, depending on the layout of the home and the ability for warm air to circulate, have the potential to heat a substantial percentage of a home. Most solid-fuel burners typically cost around $2,500 to $3,000.

While technically outside the scope of this report, one factor that can make a considerable difference to the required size of the heater (and therefore its capital cost) as well as the cost to operate the heater, is effective home insulation. With typically 40% of heat being lost through an uninsulated home's ceiling and another 10% being lost through the floor, basic building envelope insulation measures can make a significant difference to heating costs as well as reducing emissions through the requirement for a smaller heater than may have otherwise been the case.

Ventilation and heat-transfer systems

Domestic ventilation systems and similar products are ventilation systems – not heaters. They operate by removing moist air from a room, and replacing it with warmer or drier air sourced from within a ceiling cavity or outside.

Despite not being heaters, they can offer two advantages in relation to heating. Firstly, drier air is easier to heat than moist air, so a domestic ventilation system can allow a heater to operate more effectively. Secondly, a domestic ventilation system will bring in air from outside the room, which then results in some movement of air from that room into other areas. In this way it creates a flow of air from one room to another, thereby assisting the movement of warmth around a home. Installed costs typically range from $1,200 to $1,800 sourced from Consumer online (www.consumer.org.nz).

Another option that can assist with the effectiveness of home heating is a heat-transfer system. These systems involve a heat outlet in a warm room usually situated close to a large heat source such as a wood burner. Ducting is then installed from this source to one or more other rooms within a house and an in-line fan is used to distribute this air to other parts of the house. Typical costs range from $600 to $1,200 depending on the extent of ducting/outlets. There are also options available such as a speed controller, which can be used to control the fan speed and thereby the heat-transfer rate. A thermostat can also be placed in the heat-source area so that heat will not be drawn until the temperature in that room has reached a pre-set level.

A heat-transfer system could be used effectively in conjunction with a large heat source to help in distributing heat more evenly throughout a house. Note that a heat-transfer system would offer little benefit if the main heat source was only of sufficient capacity to heat the area in which it is situated.

A comment is made at the bottom of each template in section 4 as to whether the particular heating option would be suitable for operating in conjunction with a heat-transfer system.

Direct vs indirect use of fuel

This report has focused on the micro level of the use of various heating appliances in an individual home. This means that, for example, electric heaters can be shown to have zero emissions at the point of use. However, at a macro level, many electric heating systems will have an impact on the requirements for future electricity generation, which may well involve the combustion of fuel, with the consequent release of particulate, greenhouse and other emissions in some other location. The requirements to upgrade electricity transmission infrastructure would also involve significant capital expenditure, of the order of several thousand dollars per household that converts to electricity.

Another issue in this regard is whether it is more efficient, from a macro viewpoint, to burn gas directly in a gas heater than it is to burn gas at a lesser efficiency in a thermal power station and then transmit the resulting energy possibly several hundred kilometres to its point of use. In this situation the inefficiencies created via generation losses and transmission losses will need to be quantified and the full fuel-cycle efficiency considered.

Gap analysis

Although there is a range of good quality data for the PM10 emissions from solid-fuel appliances, there is a general lack of data on liquid and gaseous fuel appliances. As part of the process of approving heating appliances for Environment Canterbury's Clean Heat Project, some work has been undertaken in association with Gas Appliance Suppliers Association (GASA) to determine the emissions from a number of LPG heaters. This information has been used to infer emissions from gas-fuelled appliances. Although this will introduce some errors, it should be considered in the context of gas emissions generally being very low in comparison with solid-fuel burners.

This testing for Environment Canterbury's Clean Heat Project approval has also been applied to liquid-fuelled heaters, so some data are available for these items, but they are specific to particular models and may not necessarily be applicable across other models.

This testing has focused mainly on PM10 emissions and the calculation of heater efficiency. Data on other emissions such as NOx can be scarce, and, as noted, the primary source of this data used in this report (Scott, 2004) may not accurately reflect the emissions of current model heaters.

There is uncertainty between the relationship of emissions from an enclosed wood burner operating under real-life conditions and operating under laboratory conditions. Environment Canterbury - with funding from the Sustainable Management Fund - is currently finalising some research into this relationship, which will lead to the establishment of accepted ratios to apply to laboratory-tested emissions. Environment Waikato in conjunction with the MfE are also studying this issue in Tokoroa.

Finally, there appears to be a lack of data on the emissions, both PM10 and other, associated with electricity generation from coal and gas. Though such generation is usually undertaken at some distance from major population centres, it does effect air quality and potentially can have health impacts depending on prevailing air flows, population locations, etc.