Does Your Home Have Post-Meter Methane and NOx Emissions?

A study published earlier this year is helping draw attention to emissions from gas cooking appliances in homes. While there have been many studies of natural gas distribution system leaks, it’s important to consider what’s happening on the homeowner’s side of the gas meter.

This gas range has a recirculating exhaust hood - no exhaust to outside.

Background
The study was published in Environmental Science & Technology in January of 2022. It’s limited to stoves in 53 homes in seven California counties between January 2020 and May 2021. The sample set includes private homes, properties for sale/rent and Airbnb rentals.

The study notes on a national level, about one third of households cook with gas. In some states, that percentage is significantly higher. In California, the state in which the study was conducted, over 60% of households cook with gas.

There were 18 unique gas stove/cooktop brands among the 53 homes. The stoves ranged in age from 3 years to 30 years. The study also included gas ovens and broilers present in some of the homes.

Researchers measured methane emissions. They also measured NOx (nitrogen oxides), a combination of NO (nitric oxide) and NO2 (nitrogen dioxide).

Methane Emissions
Even though the study is small (just 53 homes), it presents some disturbing findings of leaks and incomplete combustion. The study measured when the appliance was off (not in use), on (during combustion) and when the appliance was being turned on or off (ignition or extinguishment).

The study found more than 75% of methane emissions measured originated when the appliance was off. That suggests the appliance is leaking methane, “a potent greenhouse gas”, even when the appliance isn’t in use.

The study also measured NOx levels in 32 homes and found them tied to the amount of natural gas burned.

Health Issues Result
The nitrogen oxide emissions are more interesting to us than the methane emissions. The study notes NOx emission rates are important because they contribute to the buildup of nitrogen oxides in kitchen. Air circulation, ventilation, infiltration and room size play a role in how much of the nitrogen oxides build up.

Nitrogen oxides contribute to respiratory disease. This is a known issue with a national standard for nitrogen oxide levels. The NOx levels in a kitchen can exceed the national standard in a few minutes where a range hood (exhaust) is not used or there’s poor ventilation.

Are Methane Emissions a Motivator for Homeowners?
The study notes over “a 20-year timeframe 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”. That’s probably not a surprise to most people since there’s been so much discussion about the relation between the use of fossil fuels and climate change.

People emit methane through our respiration. Cows are a significant source of methane. We wonder if the effect of methane emissions on climate change will motivate a homeowner to convert to electric cooking. We suspect it’s more likely homeowners will consider converting to electric to avoid methane and NOx emissions inside their homes.

Bans and Banning Bans
Communities in California, New York, Massachusetts and Washington have attempted to address climate change by banning gas connections in new buildings. Canada is moving in a similar direction with requirements for zero-emission space and water heating.

In response, twenty states, including Georgia, have passed laws that prohibit gas bans by local communities. In Georgia, elected officials in favor of prohibiting gas bans noted the need for long-term infrastructure planning among gas providers and the need for gas in some commercial production methods as reasons to prohibit bans.

While these are important issues, we’re more concerned with the quality of the air you’re breathing in your own home on a daily basis as it has the potential for a more immediate and severe impact. You’re probably spending more time in your home than any other place so we tend to focus on in-home health, a more powerful motivator, which may ultimately have a positive outcome for issues like climate change as well.

Steps You Can Take
If you’re concerned about this issue, here are some steps you can take:

1. Gas leaks in homes are common. Plumbers and inspectors can use a gas sniffer (a device that detects gas) to locate leaks. We would be surprised if you don’t have a gas leak in your house, especially if you have old pipes.

You can consider having an inspection of the pipes between your gas meter and appliances to determine if there are any leaks that need to be sealed. This can be challenging because the pipes aren’t always easy to access though we also find common leaks in accessible fixtures like gas regulators.

2. You can also make sure the appliances are clean. For example, cleaning the valves/controls on your gas appliance may help them close completely rather than letting some small amount of gas escape.

3. Be sure to use your exhaust hood every time you cook. Your exhaust hood should vent outside your house and be designed/sized to accommodate the size of your stove/cooktop.

4. You can work with a heating/cooling contractor if you’re concerned about the amount of air that’s being exhausted by the hood. An airflow of 400 cubic feet per minute or more requires a make-up air source so the exhaust hood doesn’t draw air from the rest of the home.

You could also choose to change your cooking method.

This six-burner gas cooktop has no exhaust to the outside. Combustion emissions remain in the house.

Alternative Fuel
If you’re concerned about having incomplete combustion, gas leaks and related issues in your home, you can consider using electric appliances for cooking. We hasten to say that electric cooking is not perfect. You’ll still need proper ventilation to remove the compounds released from cooking with oils, cooking protein, etc.

We find that people typically move to an induction cooktop if they’re changing from gas. You can try out induction cooking by buying or borrowing a “single-burner” induction cooktop. It’s portable and typically large enough to accommodate large pans like big skillets and woks or heavy items like large pots full of water for boiling pasta.

An induction cooking element with an 8-quart pot on it. The portable cooking element is placed on the existing range so the owner can still use the exhaust hood above.

Is This About Gas Appliances?
It’s not our intention to demonize gas appliances. They can work well when homeowners follow the manufacturer’s instructions for installation and maintenance. As we noted above, some of the issues resulted from homeowners not using the exhaust hood or cleaning the appliances thoroughly.

We prefer not to have combustion inside the air barrier of a home. For us, it’s about the lack of proper installation and maintenance. If deferred maintenance for gas appliances produces worse indoor air quality than an electric appliance, that’s enough reason for us to advocate for an electric appliance.

It’s important for homeowners to make informed decisions about proper appliance operation and maintenance. If you’re going to have a gas appliance, be prepared to more carefully manage the installation of the appliance and related components like exhaust or ventilation systems. You’ll also have to be prepared to clean and inspect a gas appliance more often than electric appliances to insure proper function.

In Conclusion
Even if you look suspiciously at your gas cooktop, don’t panic about the possibility of a leak or incomplete combustion. Like everything else in your home, you can lay out your plan and take steps to address any concerns - whether inspecting and repairing what you have or moving to a different fuel source for cooking.

Like so many other in-home health concerns, we’re not worried that you’ll have a catastrophic event. We’re concerned that you’ll be exposed to low-level irritants that cause health problems or aggravate other health problems.

We’d appreciate it if you’d take a moment to let us know if this is a concern for you. If so, what steps have your considered or taken?

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