2 Methodology

2.1 Selection of study areas

In addition, a national survey was carried out to provide an overall picture of domestic heating methods and fuels, and other variables relating to warm homes in New Zealand.

The resulting 30 study areas are as follows:

2.2 Domestic heating survey

The primary purpose of the domestic heating survey was to determine the home heating methods and fuels used by households in the study areas during the winter months, given that PM₁₀ concentrations in excess of the national environmental standard typically occur during winter. An additional purpose was to collect information relating to warm homes in New Zealand. In particular, data were collected on home heating methods and home insulation, age of dwelling, size of dwelling, home ownership and household income.

The survey questionnaire was structured to collect information on heating methods and fuels for all methods used in the main living area of the home. No additional information was sought on heating methods used in other areas of the home. For each heating method, the survey included questions on:

• average daily fuel use during winter (excluding electricity)
• average daily fuel use during summer (for those heating during summer months)
• average number of days per week the heating method was used for each month of the year
• average monthly (electricity, gas) or annual (wood, coal, oil) heating costs during the winter.

Additional information was collected specific to heating methods. This included:

• the proportion of wood that was self-collected versus bought (for wood options only) [This question was added to the survey after the first survey had been carried out. As a result, information on this variable is not available for the first group surveyed, which includes Gore, Invercargill, Te Kuiti and the national survey.]
• for electricity, the type of electric heater(s) used in the main living area
• for gas, whether it was mains or bottled, and flued or unflued
• for wood burners and multi-fuel burners, the age of the burner in terms of the following categories: less than 5 years, 5–10 years and more than 10 years.

The following data were also sought in the survey:

• number of bedrooms
• age of the dwelling
• whether the home was owner occupied or rented
• household income.

Additional data were collected by the survey company to ensure the respondents included a cross-section of the population. This included the age of respondent, type of household, sex, employment status, ethnic group, and number of occupants in the dwelling. These data have not been analysed for the purposes of this report.

Data shown in Table X.3 on monthly variations in heating behaviour and fuel use exclude information on seasonal variations in electricity use for domestic heating. This is because this information was collected to evaluate emissions from domestic heating to determine options for reducing PM₁₀ emissions in urban areas of New Zealand. Electricity is treated as a zero emission source for this purpose. Data from the graphs in Figure X.2 are shown in Tables X.5, X.7, X.11 and X.12.

2.3 Fuel use estimates

The survey questions relating to daily wood and coal use are based on the number of pieces of wood and the number of buckets of coal. These data have been converted to estimates of kilograms of fuel use based on the following conversion factors:

• the average weight of a log of wood is 1.9 kg
• the average weight of a bucket of coal is 9 kg.

Both conversion rates were based on work carried out by Lamb (2003) [Lamb C, 2003,Household Solid Fuel Heating: 2002 Christchurch home heating diary panel, prepared for Environment Canterbury.] for Christchurch. No studies appear to have been carried out for other areas of New Zealand. While it is uncertain whether the size of pieces of wood varies significantly across New Zealand, it would seem unlikely in the case of log burners because wood size is likely to be limited by the size of the appliances.