Still Cooking With Gas?
By Max Sherman, originally published in IEO Applications Column
The phrase “cooking with gas” started its life in the 1930s and 1940s as a marketing slogan by the gas industry. But the public, enamored with the benefits of gas cooking, soon adopted it to mean anything that was done really well. Of late, the star power of gas cooking-has dimmed as air quality concerris have made gas stoves a shady suspect. Policy makers have in places banned the technology and much has been written in the press—but is gas cooking really deserving of all that shade?
The recent kerfuffle has been due to a perfect storm of both indoor and outdoor enivironmental concerns that have come to our collective attention in the last few years, but these are not the only issues to conside Concerns increasing order of relevance ASHE include safety, outdoor air quality, decarhanization and indoor air quality (IAQ). Let us look at them individually.
Safety:
Appliance safety may not be the most relevant to ASHRAE's activities, but it is the oldest and most important issue with a cooking appliance—regardless of its fuel source. Fortunately for the public, the appliance industry is well aware of that and has developed industry standards.
Outdoor (Ambient) Air Quality:
Ideally, combustion appliances would produce only carbon dioxide and water vapor, but real-world gas appliances also produce oxides of nitrogen (NOx). Nitrogen dioxide (NO2) specifically is one of the criteria contaminants listed in the National Ambient Air Quality Standards (NAAQS). Low-NOx technology for burners is steadily improving and is required in some jurisdictions, but NOx production is not expected to go to zero, and that gives regulators cause for concern.
In some areas, household-generated NOx can be a major contribution to ozone production (i.e., smog). For such outdoor air quality reasons, California—having a lion’s share of noncompliance areas—recently announced that it intends to ban gas water heaters and gas furnaces at the end of the decade. The important thing to note about that is they did not include gas cooking appliances in that ban, although the production of NOx in cooking equipment is significantly larger than for the low-NOx burners California currently requires for water heaters and furnaces.
The reason gas stoves are not in that banned list is that such a policy does not pass a benefit-cost test. Cooking comprises a small percentage of home energy consumption, and gas cooking also comprises a small percentage of gas consumed by gas heating and gas water heating. So, the benefit to outdoor air quality in banning gas stoves would only be a few percent of the other two gas appliances; the costs, however, would be proportionately much higher.
When replacing a gas appliance with an electric one, the wiring of the house must be rated to take the maximum draw of the appliances. California envisions that gas water heaters and furnaces will be replaced by heat pumps, which are—as we know—much more efficient than electric resistance appliances and so may only require 5kW-10kW of capacity. Electric stoves, however, will require 10kW-15kW for a much smaller impact. Increasing electric capacity might be a minimal cost in a new all-electric development, but devastating in a retrofit situation.
Additionally, but importantly to many, a key cost is the loss of the utility associated with cooking with gas. To many people who cook, switching from gas to electric would be an enormous degradation of building service. The costs do not come close to justifying the benefit to outdoor air.
Decarbonization and Climate Change:
ASHRAE currently has a focus and position on decarbonization—the first step of which is energy efficiency improvement. One might naively think that replacing any gas appliance with an electric one would also advance that, but the situation is not that simple, as the type of appliance and its interaction with the electric grid is very important. A case can be made that we should not be pushing building electrification at all at the moment, but the decarbonization case for banning gas stoves, in particular, is even poorer—and for the same reasons as they are for ambient air quality: replacing a high-peak, low-energy gas appliance with an electric resistance one is not going to be a winner until green electricity is too cheap to meter.
Indoor Air Quality and Health:
ASHRAE Standard 62.2 has recently prohibited unvented space heaters based on their indoor air quality impacts. There is, after all, no doubt that nitrogen dioxide is produced and that nitrogen dioxide is an indoor contaminant of concern. If there were a good justification for banning gas stoves, it would make sense it would be IAQ.
The situation, however, is a bit more complicated than for unvented space heaters. NOx may only be produced by gas cooking, but there are a lot of contaminants produced by any kind of cooking. Even low-temperature cooking will produce water vapor, which can be problematic in some climates; high-temperature cooking like frying, roasting, searing, broiling, etc., will produce a host of contaminants including volatile organic compounds, polyaromatic hydrocarbons, and particles. Many of these contaminants, being “fresh,” will be reactive and thus can be expected to have enhanced health risks. While only gas stoves will produce combustion by-products, electric stoves will produce additional contaminants as food and particles interact with high-temperature coils. It is not clear which is worse.
Regardless, then, of the fuel source, the by-products of cooking should be vented. This, in fact, is what ASHRAE Standard 62.2-2022 requires—that there be a range hood that exhausts outdoors regardless of the fuel source. If that range hood is used, the combustion by-products should be exhausted along with the other contaminants, and the gas stove essentially becomes a vented appliance. The requirements in Standard 62.2, while demonstrably effective, are not perfect and, of course, could be improved, e.g., with higher capture efficiency or automatic operation.
Some studies, often quoted in the press, show a link between asthma and gas stoves as support for banning gas stoves. No reason exists to disbelieve the correlation, but the causal nature is in doubt. A review of these studies is beyond this column, but they certainly do not show that any significant health impact difference exists between gas and electric stoves when both have properly operated range hoods in compliance with Standard 62.2-2022. Such a study would be quite valuable.
Conclusion:
From its ventilation standards to the Epidemic Task Force, ASHRAE has shown it is a leader in indoor air quality. If gas stoves were really an inherent IAQ problem, we would have seen it long ago. More likely the IAQ problems seen are due to insufficient ventilation and/or kitchen exhaust that can happen when energy efficiency is pursued without adequate concern for IAQ or ventilation. Such problems are what standards like Standard 62.2 were written to address—and no indication exists that they have failed for gas stoves. No substantiated IAQ reason exists to restrict gas stoves in Standard 62.2-compliant homes.
If they are following industry and professional standards, those who wish to have electric cooking can do so in a safe, healthy, and environmentally responsible manner. The same, however, is true of gas cooking. While differences may exist between gas and electric cooking—and individuals may choose one over the other for their own reasons—there is no significant technical or environmental justification for a ban on gas (or electric resistance) stoves. ASHRAE members should make it clear that if one is meeting the intent of Standard 62.2, one can still be cooking with gas.