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Recently, we wrote about researchers ditching their gas stoves after measuring the high levels of dangerous indoor air pollution they produce.

Some scientists and chefs, concerned about the health and environmental impacts of gas stoves, are switching to electromagnetic induction stoves or even portable induction burners and touting some additional benefits.

These stories prompted some questions from readers. How does the energy efficiency of induction actually compare to gas? Is it worth switching if your province has a dirty power grid? Do gas fireplaces or furnaces cause indoor air pollution, too? Or propane stoves? Are newer gas stoves less polluting? Are induction stoves safe for those with pacemakers?

Here are the answers to some of those questions.

Donald M. wrote: "What is the actual energy use comparison, when for example bringing a pot of water to a boil between a new natural gas burner and an induction stove top?... Also how does that compare in dollars and cents?"

Energy Star is the energy efficiency certification and labelling program supported jointly by the U.S. Environmental Protection Agency and the U.S. Department of Energy that aims to promote the adoption of energy-efficient products and practices. A similar system exists in Canada in partnership with the federal government.

It says induction cooking tops transfer energy with approximately 85 per cent efficiency, compared to about 32 per cent for gas stoves (which transfer much of their heat to the surrounding room, not the pot and water you're boiling). The per unit efficiency for induction stoves is five to 10 per cent higher than for conventional electric resistance stoves and induction is three times more efficient than gas. EnergyStar says that if all cooking tops sold in the U.S. in 2021 used induction technology, the energy cost savings would exceed $125 million US and the energy savings would exceed 1,000 gigawatt hours. That's roughly equivalent to the amount of electric power consumed annually by 93,000 U.S. households.

We got this question from a couple of different readers. 

In Canada, some provinces rely heavily on coal and natural gas for power generation, so using electricity effectively burns fossil fuels and generates greenhouse gas emissions. Those provinces include Alberta (36 per cent coal, 54 per cent natural gas, 10 per cent renewables), Saskatchewan (40 per cent gas, 40 per cent coal with some carbon capture, 20 per cent renewables) and Nova Scotia (52 per cent coal, two per cent petroleum, 22 per cent gas, 24 per cent renewables).

Mike Henchen and Brady Seals at RMI, a U.S.-based think-tank focused on the energy transition to net zero, have looked into this kind of question. They say because induction is so efficient, "even if the electric grid were 100 per cent gas-powered, induction would use less gas than a gas stove."

It's true that coal generates almost twice the greenhouse gas emissions of natural gas per unit of energy produced when burned. But the federal government is requiring provinces to phase out power generation from coal by 2030. Alberta, Saskatchewan and Nova Scotia all have plans in place to do that. Ottawa has also set a deadline of 2035 for reaching net-zero electricity generation.

"The grid is getting cleaner quickly," Henchen and Seals noted in an email. "An induction stove installed today will outlive coal power in these provinces and will have lower greenhouse gas emissions on a total lifecycle basis than a gas stove."

They added that switching to induction also reduces exposure to indoor pollutants such as carbon monoxide and nitrogen dioxide, which can reach levels during cooking that "would be illegal outdoors."

WATCH | Why gas stoves are bad for the climate — and you:

A quick survey of appliance sellers in Canada shows that the lowest-end induction stoves cost a few hundred dollars more than the lowest-end gas stoves, starting at close to $1,000 for just a cooktop and under $1,500 for a range including an oven, compared to as little as $600 for a gas cooktop and $900 for a range. Both they are more expensive than conventional electric stoves, which start at around $600 for a range.

Switching from gas to electric can also add some infrastructure costs. According to Carbon Switch, a U.S.-based website that provides research and guides to help people live more sustainably, an induction stove requires a dedicated 220-volt outlet protected by 40-to-50 amp breakers. While that's similar to what's needed for other electric stoves, gas stoves only need a 120-volt circuit, so going electric might require some upgrades.

"You may need to install high-capacity wiring," writes Mara Abbott with Carbon Switch. "You might also need to upgrade your electric panel with a two-pole circuit ... And you will probably need to pay a plumber to cap your gas line."

She said that can total a few hundred to a few thousand dollars.

Finally, induction only works with cookware that sticks to a magnet, so if yours doesn't do that, you may need to invest in new pots and pans.

If that all sounds too expensive, you can start off with a portable single-burner cooktop, which plugs into any outlet and can be purchased for under $100. Those are popular with chefs such as social media celebrity Jon Kung. He's used them for pop-up restaurants at nightclubs and bars with little space and ventilation.

Dave R. of Innisfil, Ont., asked if the nitrogen oxides — contaminants linked to negative health impacts such as asthma — are naturally found in small amounts in the gas or come from burning it.

The answer is that they're produced during burning, when nitrogen and oxygen in the air react with each other due to the heat from the burning gas. 

Meanwhile, carbon monoxide is produced by incomplete combustion of the gas.

Eric Lebel, research scientist at PSE Healthy Energy in California and lead author of a recent study on pollution from gas stoves, said his team is starting to look at natural gas composition in different cities, including Toronto and Vancouver.

While it's mostly methane, he said, "there could be other pollutants in the gas as well." Those could include volatile organic compounds and sulphur compounds used to make natural gas — which is normally odourless — smelly and therefore detectable when there are leaks.

Of course, some pollutants are generated from heating cooking ingredients such as oil and fat (and any food you burn) regardless of what kind of stove you use, so turning on the hood fan is a good idea.

While our stories dealt with natural gas stoves, Peter Gosse of St. John's, N.L., has a different kind of gas stove, and wrote in to ask how it compares.

University of Saskatchewan professor Tara Kahan, who has studied pollution from stoves, said high levels of nitrogen oxides are also emitted during cooking with propane stoves, so the health impacts would be expected to be similar: "From an air quality perspective, it's not an obvious improvement over methane."

Lebel said the pollution from cooking with propane is something his team is "actively studying."

LISTEN | Cooking without gas: Why cities are cutting methane from homes:

He acknowledged that the climate impacts are expected to be lower with propane. That's because natural gas is made of methane, itself a greenhouse gas much more powerful than carbon dioxide. Lebel's research showed it leaks into the atmosphere even when the stove isn't in use. 

"We aren't as concerned about leaks of propane since it isn't a strong greenhouse gas like methane is," Lebel said. "However, CO2 is still produced upon burning it, the same way that it is produced from methane."

As part of Lebel's study, researchers looked at stoves that were between three and 30 years old. 

The study found no relationship between either the age of the stove or the purchase price when it came to methane or nitrogen oxide emissions, once the energy output (which affects emissions) was taken into account.

Rob Jackson, a professor at Stanford University who co-authored that study, said there are lots of connectors running between the stove and the natural gas networks, all of which leak a little. "Often, even when they're installed properly, there's no way to seal the system properly."

WATCH | The debate over gas and induction stoves:

Maintenance may reduce CO emissions to some extent. In the U.S., since 1926, kitchen ranges have been allowed to emit up to 800 ppm of CO (far higher than the Environmental Protection Agency exposure standard of nine ppm), according to an article by T.H. Greiner, an engineer with Iowa State University: "A new range may emit as much as the old range." However, the article says field technicians report that most kitchen ranges can be tuned to produce less than 50 ppm.

Lorraine M. asked: "Any research done on gas fireplaces and furnaces having the same effect as stoves?"

While gas fireplaces, furnaces and hot water heaters all burn and leak methane, and are thus a concern from a climate perspective, Lebel and Jackson say there's less of a worry than with gas stoves from a health perspective.

That's because, unlike stoves, they are generally required to have a vent (or chimney) to the outside. 

Jackson said, "I don't really expect gas fireplaces to be that big of a source of indoor air pollution." But he added that his team is starting to measure them to find out for sure.

Furnaces and water heaters also tend to be in areas such as basements, where people spend less time than in kitchens.

That said, Michael Thomas, founder of Carbon Switch, blogged out his experience measuring nitrogen oxides in his home earlier this year, and found they spiked in the early morning when the furnace was on, suggesting that pollutants were leaking from the furnace.

Thomas tested his air with an air quality monitor that he purchased online. He said the ones that measure nitrogen oxides are, unfortunately, expensive (about $300 US; one Canadian retailer is selling the model Thomas has for more than $450 Cdn) and hard to find.

If you're interested in other kinds of pollutants and you live in Toronto or Vancouver, you can volunteer for the next part of Lebel's study, which takes place in May. 

This part of the study won't test for pollutants from burning the gas, such as nitrogen oxides, but pollutants in the unburned gas from your stove.

It's true that the magnetic fields generated by induction stoves can interfere with devices such as pacemakers and insulin pumps.

Organizations such as the British Heart Foundation and induction stove manufacturers say people with such devices should keep them 60 centimetres away from an induction cooktop when it's on.

Have questions about this story? Send an email to ask@cbc.ca.

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