This research looks at the health impacts of using gas stoves, unflued gas heaters, open fires and wood burners in New Zealand homes.
The work was commissioned by EECA to contribute to our evidence base relating to household energy use in New Zealand.
About the research
The research was conducted by Emission Impossible Limited, with economic modelling support from Resource Economics.
The study looked at the impacts of nitrogen dioxide (NO2) and particulate matter (PM2.5) emitted indoors from using different types of appliances for heating and cooking.
The study focuses on the direct emission of combustion pollutants into the home. For the gas appliances considered, this happens during normal use and is mitigated by ventilation (from windows and extractor fan use). For wood burning, combustion emissions vary depending on the temperature of the fire, and spike during refuelling, when the door is open.
Indoor Combustion Study [PDF 1.2 MB]
Summary of report findings
The study found that the use of gas stoves, unflued gas heaters, open fires and wood burners result in the emission of harmful pollutants into the home.
The study found that the amount of exposure to pollutants depends on the appliance, with open fires and unflued gas heaters being the most harmful, followed by gas stoves, older wood burners, and then modern wood burners.
Converting this pollution exposure into health harm, the study estimated the total social cost of indoor air pollution from combustion appliances to be in the order of $5 billion dollars per year. It further estimated the fiscal cost of health treatment and restricted activity at $102 million dollars a year.
Research methodology and considerations
Methodology
For each appliance the researchers:
- Reviewed the domestic and international evidence to determine how much incremental annual indoor air pollution was associated with each device — NO2 for natural gas, and PM2.5 for wood burners.
- Applied exposure response functions to determine the health impacts caused by this incremental exposure to NO2 or PM2.5.
- Converted this health harm into economic (social) and fiscal (health system and restricted activity day) costs. Social costs are driven by the Treasury estimates for the value of a statistical life, while fiscal costs are driven by the cost of hospitalisations and treatment, and restricted activity.
Considerations
This study is about additional exposure connected to appliance use — rather than outdoor air pollution that also impacts air quality in your home. Outdoor air pollution is well known and evidenced and is principally linked to wood smoke from domestic wood burners and tailpipe emissions from traffic.
- The findings are not applicable to flued gas space heaters, outdoor gas water heater califonts, or outdoor cooking.
- A literature review was carried out to determine the best sources and methods for estimating exposure based on real-world testing in New Zealand and around the world.
- The level of NO2 exposure was estimated using New Zealand evidence, benchmarked against more recent international evidence. The annual exposure level used in this study is in line, or lower, than estimated in these recent international studies - which reflect the current mix of recent appliances.
- This data and modelling include ventilation, window use, and extractor fan use — in line with the real-world efficacy and prevalence of these mitigations.
- The study averages across a diverse set of environments; its findings are an estimate of the overall statistical cost of indoor air pollution from combustion — rather than an estimate of the individual cost to a given household of an appliance.
- The research has been peer reviewed in New Zealand and benchmarked against international evidence. An international peer review will also be conducted.
- The results will be used by EECA to inform future cost-benefit analyses and are best understood as part of a wider analysis of energy system costs.
Next steps
EECA will continue to unpack the findings included.
Insights from this report will contribute to shaping EECA programmes, including future public information efforts.
EECA is working though the best way to integrate these findings into the Warmer Kiwi Homes programme, which currently funds a small number of low emission wood burners.