Ventilation Isn’t Enough To Make Gas Stoves Safe

The most effective way to protect human health is to phase out the fossil fuel-powered appliances.

Earlier this week, the US Consumer Product Safety Commission (CPSC) announced they would consider regulating the sale of new gas stoves. The announcement came after a group of researchers found that 650,000 childhood asthma cases can be attributed to gas stoves. 

In response to the CPSC’s announcement, industry groups like the Association of Home Appliance Manufacturers, deflected blame and said the problem isn’t gas stoves in homes, but poor ventilation systems. 

“Ventilation is really where this discussion should be, rather than banning one particular type of technology,” Jill Notini, an executive at the industry group, told Bloomberg. 

But according to many indoor air pollution experts, ventilation is an incomplete solution if the goal is to improve public health and protect children from the risks of gas stoves.

Many range hoods are ineffective

As I wrote earlier this week, gas stoves produce nitrogen dioxide (NO2), a pollutant that is harmful to human health at high enough concentrations. 

“Nitrogen dioxide irritates your respiratory system,” Josiah Kephart, a researcher who studies indoor air pollution at Drexel University, told me. “As you breathe it in, all of the lining throughout your entire respiratory system gets irritated or inflamed.”

Numerous studies over the years have shown that homes with gas stoves consistently have dangerously high levels of NO2. As a result, children living in a home with a gas stove have a 42% increased risk of asthma.

In order for a ventilation system, like a range hood, to be effective at reducing indoor pollution levels, it needs to do two things: capture pollutants like NO2 and then get them out of the home. But many range hoods don’t do this effectively.

One of the most popular types of range hood sold in the United States is what manufacturers call a “ductless hood.” Often these ventilation systems are attached to microwaves making them cheap and relatively small, hence their popularity. The problem is that these hoods don’t send pollution outside; they simply recirculate the air throughout the kitchen. 

Data on kitchen ventilation systems in the United States is hard to come by. But one estimate put the number of ductless hoods at 50%. Most state’s building code doesn’t require range hoods to be vented outside.

Range hoods that exhaust pollution outside have their problems too, though. Numerous studies have shown that even high-performance range hoods don’t remove enough pollution to prevent health risks. 

In 2012 researchers at Lawrence Berkeley National Laboratory (LBNL) measured the performance of 15 range hoods installed in California homes. For years, California has had one of the strictest building codes; the state requires high-performing range hoods in every kitchen. But the researchers found that these code-compliant hoods captured just 55% of pollutants like NO2. Even with universal range hood use, LBNL estimated that 18 to 30% of people would still be exposed to NO2 levels that exceed the World Health Organization’s (WHO) guidelines. 

That same year researchers at LBNL found that the average Energy Star-rated range hood only captured 30% of pollutants.

Range hoods perform poorly in the real world

All of LBNL’s studies were done in the lab. But indoor air pollution experts I spoke to pointed out that even the best range hoods don’t always function well in people’s homes.

“What we see when we take these range hoods or these ventilation systems out into the real world, is that the protection is not something you can rely on,” said Kephart, who has run indoor air quality tests in thousands of homes. 

In 2014, a group of researchers in Baltimore ran a study with 78 homes with gas stoves to understand the most effective ways to reduce indoor air pollution. In one group of homes, they replaced gas stoves with electric stoves. In this group, NO2 pollution levels fell by 50%. (Kephart told me the remaining NO2 probably came from cars and other sources of pollution outside). In another group of homes, they gave homeowners an air purifier with a carbon filter and NO2 levels fell by 22%. In the last group, they installed range hoods. In this final group they found no significant difference in NO2 pollution. 

“The industry talks about the best case scenarios for air quality and ventilation,” said Rob Jackson, a researcher at Stanford. “In practice, we don't typically find the best case scenarios in people's homes.”

In a recent study, Jackson and his team found that many gas stoves leak pollution even when they are turned off. This is a problem both for human health and the environment. They discovered that the methane leaking from gas stoves is responsible for as much greenhouse gas emissions as 500,000 gasoline-powered cars.

Most people don’t use their range hood

The best range hood in the most optimal environment only works if someone turns it on. But researchers have consistently found that most people don’t do that. 

A 2003 study found that 28% of survey respondents reported using a kitchen exhaust fan when cooking with burners. In 2011, another group of researchers found that 34% of people reported using their range hood while cooking. 

Brady Seals, an indoor air quality researcher at Rocky Mountain Institute, told me that most of those studies were self-reported. But when researchers look at how often people actually use their range hood, it’s generally half of what they claim in a survey. 

In most studies, people report the loud noise of their fan as the main reason they don’t use their range hood. In their research on range hood performance, researchers at LBNL found that the highest-performing models—that is, the models that actually reduced indoor air pollution—produced sound levels too high for normal conversation. 

Researchers still recommend using range hoods as much as possible

Despite all of their problems, everyone I spoke to for this story recommended that people install range hoods and use them every time they cook if possible. 

“When people ask me what they should do, job one is to get a good range hood,” said Max Sherman, a building physicist who spent much of his career at LBNL. 

Sherman told me the most important metric to look at is the capture efficiency. Frustratingly, most manufacturers don’t put this number on their product labels. No building codes mention it either. But he said the size of a range hood is a good indicator of its capture efficiency.

“You can eyeball it by how much volume is within the metal or glass or whatever the thing is made of,” he said. “The more volume that it captures, the better it's going to be at exhausting the stuff.”

Research from LBNL has consistently shown that cooking on a back burner is better than cooking on a front burner since it helps the range hood capture more pollutants. The researchers I spoke to also recommend people avoid “ductless” range hoods that recirculate air throughout the kitchen. 

It’s better to prevent pollution from entering the home

But most of the experts I spoke to for this story told me that it doesn’t make sense to design policy based on best case scenarios and ideal human behavior. For these reasons, all of them support policies that would eventually phase out gas stoves. 

Jonathan Wilson, a director at the National Center for Healthy Housing, said that in numerous studies he’s found ventilation to be ineffective. For that reason his organization recently recommended phasing out natural gas in new construction.

“If the gas industry can document that [ventilation] has a positive effect then we can reconsider that. But it’s just not happening,” he said. “People are getting sick because of these gas stoves.”

Kephart also supports phasing out natural gas in new construction. He said the most effective solution is to prevent pollution from getting into people’s homes in the first place. 

“In my field of environmental health, you always want to stop the pollution as early as you can in the process,” he said. “If we're creating this pollution inside of our homes and then relying on this fan to blow the pollution right past our faces, it doesn't make any sense.”