For those of us who enjoy cooking meals with natural gas, there’s a warning from scientists at Stanford University.
You may have heard that natural gas stoves generate carbon dioxide by burning natural gas as a fuel. It makes sense.
But natural gas stoves also leak unburned methane into the air, a greenhouse gas that’s 86 times as potent as carbon dioxide (CO2) over a 20-year period. Researchers found that this leaking has a climate impact comparable to the carbon dioxide emissions from a half-million cars.
Home methane leaks contribute to a third as much warming as the carbon dioxide generated by combustion during cooking. Gas stoves also can expose users to respiratory, disease-triggering pollutants like nitrogen oxides (NOx).
If you’re not using a range hood to ventilate your kitchen, you could surpass U.S. Environmental Protection Agency guidelines for outdoor NOx exposure within a few minutes of cooking. There aren’t any indoor standards.
“One of the big take-homes from the study is that using gas stoves simultaneously harms the environment and our health through the gases they emit,” says lead author Eric Lebel, who conducted the research as a graduate student in Stanford’s School of Earth, Energy and Environmental Sciences (Stanford Earth).
“Gas stoves are unique among the gas appliances in a home because the emissions are not currently required to be vented in many places and they sit in an occupied place in the house.
“Anytime a stove user turns on the gas stove, they are producing some level of NOx. Whether that NOx exceeds the health threshold depends on whether the user has turned the hood on, how big the kitchen is, what the ventilation in the room is, and how many burners and how high they were turned on.”
Advice to Homeowners
Lebel’s main advice is to use your range hood every time you use a natural gas stove to minimize concentrations of NOx and other pollutants in the kitchen.
“Methane emissions aren’t a health hazard or safety hazard in the homes we measured, but definitely get your stove checked anytime you can smell gas.”
He adds: “the emissions of methane that we measured from stoves nevertheless increase the climate impact of the stove by 39% over a 20-year time horizon compared to the CO2 that would be emitted from burning the gas to cook.”
The climate and health impacts of natural gas stoves are a known problem. New York is considering a ban on natural gas connections in new buildings and dozens of local governments have taken similar action. A third of U.S. households, or more than 40 million homes, cook with gas.
“Definitely, there have only been a handful of studies looking at emissions from residential appliances and all these studies highlight that more research is needed in this field,” says Lebel, currently a senior scientist at PSE Healthy Energy.
“... We decided to do this research as part of an effort to understand emissions from appliances in homes. Previous work looking at methane emissions from cities and comparing city-wide emissions to source-specific emissions showed that there were missing sources of methane in cities, which is what inspired this research on residences in the first place.”
The researchers measured methane and NOx concentration in 53 California homes, during ignition, combustion, extinguishment and when the stoves were turned off.
Eighteen brands ranging in age from three to 30 years were tested. Age didn’t seem to matter.
Most surprising, the researchers say, more than three quarters of methane emissions occurred while the stoves were turned off, suggesting that gas fittings and connections and in-home gas lines are responsible for most emissions.
Go Electric?
Stanford scientists say switching to electric stoves will cut greenhouse gas emissions and indoor air pollution. But what about coal, which is still used for almost 20% of electric generation in the U.S.? Natural gas comes in at 40%, according to U.S. Energy Information Administration.
Lebel notes that the country is rapidly cleaning up its electricity supply.
“In many places, like here in California, electricity is produced from cleaner sources and we are on a trajectory for many places to move in that direction soon. In order to fully achieve a carbon-neutral energy infrastructure, we need to phase out from fossil fuels to electric appliances, a process which will take time especially in homes which already have gas infrastructure. You can take the carbon out of the electricity, but you can’t easily take it out of the fossil fuel.”
Natural gas stoves also emit carbon monoxide and formaldehyde. And there are other methane emissions to consider.
“We found that the methane emissions from stoves, for instance, increase the carbon impact by 39% compared to when just CO2 emissions are considered,” he says. “And that’s only leakage at the appliance-level, it doesn’t incorporate leaks from the rest of the supply and distribution chain, all of which can leak additional methane gas as the gas is produced and distributed, etc.”
He adds that electric stoves have not been shown to produce NOx gases or other pollutants just from using the heating element, as Stanford and other researchers have found with gas stoves.
Scientists haven’t shared their findings with gas stove manufacturers, Lebel says, “but I would be delighted to see future studies work with manufacturers to better understand what might be causing these leaks and if there is an easy way to fix them.”
