Health Impacts and Costs of Indoor Combustion in Aotearoa New Zealand
24 September 2025
Study by Emission Impossible Ltd & Resource Economics
Our study estimated the costs to society of health impacts associated with emissions of harmful air pollutants from wood burners, gas stoves and unflued gas heaters commonly used in New Zealand homes.
The appliances assessed included gas stoves and unflued gas heaters as well as a range of wood burners from ultra-low emission burners and standard, modern burners through to (polluting) open fires. The pollutants assessed were the two most critical air pollutants linked to adverse health effects in New Zealand – fine particulate (PM₂.₅) and nitrogen dioxide (NO₂).
In the first phase of the study, we undertook a comprehensive literature review to estimate annual indoor concentration increments for PM₂.₅ and NO₂. This found high levels of heterogeneity in the literature due to the complexity of factors contributing to indoor air quality and inconsistencies in the way that data are collected and reported for different research purposes. Preference was given to high quality New Zealand data, benchmarked against the latest evidence in the international literature.
The focus on annual exposure reflects World Health Organisation guidance on the significance of chronic exposure relative to acute exposure. Our approach was consistent with other large studies on the impacts of gas stoves and wood burners in Europe and the United States.
We then combined estimated annual increments for each pollutant with New Zealand-specific exposure-response functions (Hales et al., 2021) and household composition data to determine estimates of mortality and morbidity health impacts. The costs associated with each impact were then updated to current values (2025 dollars or 2025$).
When considered at the national level, the health burden and economic impacts of indoor combustion were substantial, totalling 2025$5.6 billion.
Just over 200 premature deaths per annum were attributed to indoor exposure to NO₂ from around 360,000 gas stoves and another 100 premature deaths per annum attributed to indoor exposure to PM₂.₅ from 524,000 wood burners. Notably, the modelled impacts of indoor air pollution are a similar order of magnitude to the modelled impacts of outdoor air pollution. This is consistent with the WHO Global Burden of Disease study which estimated similar annual impacts from household air pollution (3.2 million deaths globally) and outdoor air pollution (3.5 million deaths globally, WHO 2024).
Total estimated annual indoor air pollution impacts for Aotearoa New Zealand
| Cases of Modelled Health Outcome | Gas Stoves | Wood Burners* | Unflued Gas Heaters |
|---|---|---|---|
| (Estimated number of appliances) | (360,099) | (523,686) | (44,645) |
| Premature mortality (>30 years) | 208 | 101 | 57 |
| Cardiovascular hospitalisations (all ages) | 236 | 255 | 66 |
| Respiratory hospitalisations (all ages) | 775 | 191 | 211 |
| Restricted activity days (all ages) | - | 167,204 | - |
*All wood burner types (open fire + non-NES + NES compliant + ultra low emission + pellet burners). For further details of underlying assumptions and calculations refer body of report.
Total estimated annual indoor and outdoor air pollution costs for Aotearoa New Zealand
| Appliance | Indoor Air Pollution Costs (2025$M) | Outdoor Air Pollution Costs (2025$M) |
|---|---|---|
| Electric stove | Reference case | Reference case |
| Gas stove | $3,308 | $0 |
| Wood burner type 1a (open fire) | $105 | $53 |
| Wood burner type 1b (non-NES) | $777 | $1,718 |
| Wood burner type 2 (NES compliant) | $673 | $4,560 |
| Gas unflued heater | $912 | $0 |
| National Total 2025$M | $5,851 | $6,484 |
Estimates assume wood burner or unflued gas heater is main heating source and includes health outcomes specified in HAPINZ 3.0 (only). For further details of underlying assumptions and calculations refer body of report.
*including open fires, pellet burners & ultra-low emission wood burners (not shown)
One of the issues for this study is whether the impacts of indoor air pollution are a subset of the total effects of air pollution or if they are additional. Our literature review found no correlation between indoor and outdoor air pollution for NO₂ and PM₂.₅. Consequently, we are confident there is no double counting in the method we have used to assess the effects of indoor air pollution by appliance.
The national estimates of health impacts and costs from indoor air pollution are significant and serious. It is important to note that this study considers only the health outcomes specified in the Health and Air Pollution in New Zealand 3.0 study (Kuschel et al 2022). This means that these identified impacts are an underestimate of the actual impacts of air pollution more broadly on society.
The results of this study will give EECA the ability to better estimate the impacts of gas stoves, wood burners and unflued gas heaters, and to inform future policy settings for wood burners in residential settings.
Full study located here.
Helpful notes from Lou
What can I do to improve my indoor air quality if I have a gas stove?
Open a window at all times you are cooking with gas. Leave it open for a little while after too, to let the pollutants (and steam and fine particles) disperse. Fresh air is your friend.
This is in addition to always using the extractor fan. Our literature review showed no reduction in measured NO₂ concentrations with range hoods on. We were pretty surprised by this and are still speculating as to why.
What can I do to improve my indoor air quality if I have a wood burner?
Minimise the time the door is open for reloading - this is when emissions from the wood burner can leak into the indoor living space.
Another way to get better performance from your wood burner is to regularly clean the flue. Studies show this can make a significant reduction in emissions. It’s also a typical insurance requirement that you may not be aware of.
What can I do to improve my indoor air quality if I have an unflued gas heater?
Don’t use it indoors. Seriously - these things should be banned. (But if you have no choice - muchas empathy & open a window)
Any other tips?
We were surprised to find out that the primary source of PM₂.₅ in New Zealand homes was cooking - any type of cooking - not just gas stoves with combustion. So it’s a really good idea to open a window and improve ventilation when cooking.
Other significant sources of fine particles indoors include smoking, candles, incense and vacuuming (ha! less vacuuming more relaxing we say).