New stoves reduce emissions of particulate matter

Statistics Norway now presents the results of a survey financed by the Norwegian Public Roads Administration. The results show that if all the old wood-burning stoves were replaced by new, less polluting stoves, the emissions of particulate matter from this source would be reduced by two thirds, or 400 tonnes, in each of the two towns.

The effect of reduced emissions due to replacement of old stoves has been dampened somewhat because the high electricity prices in the winter of 2002/2003 resulted in increased use of fuelwood; the number of households who used wood-burning stoves increased by 4-6 per cent in Trondheim and Bergen. Still, 5 000 and 8 000 households respectively did not use their wood-burning appliance that winter. This means that the emissions would be a great deal higher if more stoves were being used.

New stoves with lower emissions

In 2001, more than half of the emissions of particulate matter in Trondheim and more than 60 per cent in Bergen were generated by residential wood combustion. The other main source was road traffic. Fuelwood use accounts for such a large proportion of these emissions because most of the wood is still burned in polluting stoves produced before 1998 (old technology). Old stoves emit on average 33 grams of particulate matter per kilo of wood. In comparison, new, and certified stoves produced after 1998 emit 6.2 grams of particulate matter per kilo of wood.

The survey reveals that in the winter of 2002/2003, 25 per cent of the fuelwood in Trondheim and 20 per cent of the fuelwood in Bergen was burned in new stoves. More than two thirds of the fuelwood was burned in old stoves, while the rest (3 per cent in Trondheim and 12 per cent in Bergen) was burned in open fireplaces.

Emissions can be reduced further

The results of the survey show that two thirds of the wood was burned in old stoves, which contributed to more than 80 per cent of the particle emissions. New stoves accounted for only 5 per cent of the emissions, even though more than 20 per cent of the wood was burned in such stoves. This means that because most of the wood is burned in old stoves, emissions can be reduced considerably in Trondheim and Bergen without changing heating habits or wood consumption. If the old, polluting stoves were replaced by new stoves emissions of particulate matter would be reduced by more than three quarters, or 400 tonnes, both in Trondheim and Bergen. But because some of the old stoves are antique this is a controversial issue.

There is little reason to believe that the consumption of wood will be stable over time. Because new stoves burn the wood more efficiently the consumption of wood will go down as more households replace their old stoves with new ones, provided that all other factors (temperature, price of electricity and wood, number of stoves, and wood supply) stay unchanged.

Although it is possible to reduce emissions considerably in the future, it is important to remember that there has already been a great reduction. In both Trondheim and Bergen, the emissions of particulate matter would have been about 140 tonnes higher if none of the old stoves had been replaced. In Trondheim, households who have changed to new stoves have contributed to reduce particle emissions by 20 kilos a year. In Bergen, the corresponding figure is 16 kilos a year.

More households use wood for heating

The survey reveals that the number of Bergen households that use wood for residential heating was 6 per cent higher in the winter of 2002/2003 than in the previous winter. In Trondheim, the increase was 4 per cent. Among those who used wood for heating in 2002/2003, there is a mix of people who had installed a new stove for the first time and people who started using their fireplace again after a period of disuse. The impact on emissions is strongest if these fireplaces consist of old stoves because they emit five times more particulate matter than new stoves.

Although more households used wood for heating in the winter of 2002/2003 than in the winter of 2001/2002, this does not necessarily result in higher consumption of wood. In fact, six of ten households said that they used about the same amount of wood both winters. Those who said that they used more wood did so because the winter of 2002/2003 was particularly cold or because of higher electricity prices.

Fuelwood use in Trondheim

According to the Population and Housing Census 2001, there are 69 000 dwellings in Trondheim. More than half have wood-burning appliances. The results of the survey show that in one out of eight dwellings, the fireplace was not in use during the winter of 2002/2003. If increased electricity prices or other conditions result in all the fireplaces being used, this will imply increased wood consumption and higher emissions. 32 600 dwellings in Trondheim used wood for heating. About three quarters of the wood was burned in old stoves, one quarter in new stoves. Only 3 per cent of the wood was burned in open fireplaces.

Figure 1 shows the emissions of particulate matter (PM ₁₀ ) from the use of fuelwood in Trondheim, divided by urban district.

Fuelwood use in Bergen

According to the Population and Housing Census 2001, there are 105 000 dwellings in Bergen.

Nearly 50 000 have wood-burning appliances. The survey shows that the fireplace was used in six out of seven dwellings during the winter of 2002/2003. If increased electricity prices or other conditions result in all the fireplaces being used, this will imply increased wood consumption and higher emissions. Two of three fireplaces are old, polluting stoves. 70 per cent of the wood in Bergen is burned in old stoves, 20 per cent in new stoves and 10 per cent in open fireplaces.

Figure 2 shows the emissions of particulate matter from fuelwood use in Bergen, divided by urban district.

Use of fuelwood mostly during daytime

Residential wood combustion takes place mainly in the afternoon and in the evening. Less than one per cent of those who used fuelwood in Trondheim and Bergen used their stoves during the night. We have to assume that the number of fuelwood consumers and how much the stoves are used depend on the weather, and the survey confirms this: Eight of ten fuelwood consumers use more wood on a cold winter day than on a warm winter day. Less than ten per cent of the fuelwood consumption in Trondheim and Bergen in the winter of 2002/2003 was used merely because it is cosy. The corresponding figure for Oslo in the winter of 2001/2002 was much higher, at 25 per cent. 98 per cent of the respondents also used other energy sources than fuelwood for heating. More than 60 per cent of the fuelwood consumers in Trondheim and Bergen used electricity as their main heating source. Fuelwood was the main heating source for 20 per cent of the users.

Replacement of stoves regardless of environmental issues

Respondents who had replaced their old stove with a new one were asked why they had done this. They could select more than one answer if applicable. 16 per cent had done so because of the warmth and comfort that the new stove brought. Improved heating and reduced electricity consumption were also important factors, but in Trondheim and Bergen the majority of the respondents said that they replaced their stoves because of wear and tear. Only 1-2 per cent said that they bought a new stove because they are more environmentally friendly. In the Oslo survey, 3 per cent said that environmental considerations were the main reason for the change to a new stove.

Air quality forecasts

Data from the survey will be included in the models of air quality prognoses in Oslo, Bergen and Trondheim. The new data will result in an improved basis for the prognoses, and reduce the uncertainty in the air quality forecasts. These forecasts can be found each day on www.luftkvalitet.info/byer and in local newspapers.

Read more about fuelwood combustion and emissions to air

Survey of use of fuelwood and heating habits in Trondheim and Bergen 2003 (Report 2004/27 from Statistics Norway) .
(Report in Norwegian, with English summary.)

The Oslo survey 2002 (Report 2004/5 from Statistics Norway) .
(Report in Norwegian, with English summary.)

Utslipp til luft fra vedfyring i Norge (Emissions to air from fuelwood use in Norway) (Report 2001/36 from Statistics Norway) .
(In Norwegian.)

Utslipp til luft i norske kommuner (Emissions to air in Norwegian municipalities)

www.luftkvalitet.info/byer (Air quality in Norwegian towns)

The Norwegian Pollution Control Authority

Tables:

• Table 1 Number of dwellings with and without wood-burning fireplaces. Trondheim, Bergen and Oslo. 2002/2003
• Table 2 Number of households by the type of fireplace that are most used. Trondheim, Bergen and Oslo