A limited study in California provides one more reason to ditch the gas kitchen range and convert to electricity.
Researchers estimate that the more than 40 million gas stoves in U.S. kitchens emit significant amounts of methane even when they are turned off. Methane is a major component of natural gas, 86 times as powerful as carbon dioxide for global warming when measured on a 20-year timescale.
The study, published in the journal Environmental Science & Technology late last month, measured the methane released by kitchen stoves in 53 homes. The Stanford University researchers measured leaks when the stoves were off (what they called “steady-state-off”), when the burners were on, and in the transition periods when burners were being ignited or turned off. Between 0.8% and 1.3% of the natural gas that stoves use in all is emitted as unburned methane, adding up to total U.S. emissions of 28 gigagrams (Gg) of methane annually.
“More than three-quarters of methane emissions we measured originated during steady-state-off,” the report says. “Using a 20-year time frame for methane, annual methane emissions from all gas stoves in U.S. homes have a climate impact comparable to the annual carbon dioxide emissions of 500,000 cars.”
In addition to methane releases, stoves also produce nitrogen oxides when stove top burners or ovens are on, which can trigger respiratory disease. In fact, households that do not use range hoods or have poor ventilation can exceed the national standard for nitrogen dioxide with just a few minutes of stove use, especially in smaller kitchens, the report says.
The report comes at a time when cooking and heating appliances that run on natural gas and other fossil fuels are already in the crosshairs in a number of U.S. and Canadian communities as regulators look for ways to slow global warming. More than 20 cities in California, including San Francisco and Berkeley, have passed laws that would prohibit the use of natural gas in new buildings. Earlier this year, New York City got on the bandwagon with a ban on gas connections in new buildings, joining cities in Massachusetts and Washington. In Canada, a requirement for zero-emissions space and water heating went into effect on Jan. 1, in Vancouver, and Quebec outlawed oil-fired heating equipment in new construction at the start of the year.
However, at least 20 states, including Arizona, Georgia, Florida, and Texas, have passed laws that prohibit gas bans. The gas industry also has fought the restrictions, and gas ranges remain popular with many cooking professionals.
The researchers, all from the Department of Earth System Science at Stanford University, said that natural gas leaks from the 3 million miles of pipeline in the U.S. have been studied extensively. But much less work has been done to understand gas emission inside houses, what they called “post-meter emissions.”
Emissions from gas stoves are an especially ripe area for research. More than one-third of all U.S. households use natural gas for cooking. In California, 60% of all households cook with gas.
“Among all gas appliances, the stove is unique in that the byproducts of combustion are emitted directly into home air with no requirement for venting the exhaust outdoor,” the report says. “In fact, some kitchens have ‘ductless’ hoods that recirculate fumes through activated charcoal filters, which are generally less effective at cleaning the air.” Range hoods vented to the outside are more effective, but they are used only 25% to 40% of the time.
Researchers measured emissions in private homes, homes for sale or rent, and in Airbnb rentals, and studied both gas cooktops as well as ovens and broilers. Stoves ranged in age from 3 to 30 years. Results suggest that “most stoves and associated nearby piping leak some methane continuously.”
Methane emissions from a single burner during combustion were more than four times higher than when the entire stove was turned off, but the length of time during the day when burners are idle is much longer.
- Emissions from one on-off pulse for a single burner equaled the amount of gas emitted during 10 minutes of steady combustion.
- Burners lit with an electronic sparking device emitted less methane than cooktops with pilot lights.
- The age and price of the stove did not affect methane emissions.
The authors said they quantified steady-state-off emissions from stoves because they had not been included in most previous studies of cooktop emissions, and because previous research had found that steady-state-off emissions were a “substantial, sometimes dominant” component of total methane emissions from tank-style water heaters.
Scott Gibson is a contributing writer at GBA and Fine Homebuilding magazine.
Get building science and energy efficiency advice, plus special offers, in your inbox.