Natural Gas Methane Emissions From California Homes

Methane emissions from the natural gas system likely contribute a small but meaningful fraction of California’s greenhouse gas emissions. This work estimates statewide mean methane emissions from residential natural gas consumption using measurements of inactive, house leakage (pipe-fitting leaks and combustion appliance pilot light flames) and, separately, a subset of operating combustion appliances in 75 California homes that participated in energy efficiency retrofit programs.
The measurements show inactive house emissions mostly near the limit of detection but with a small number of emissions above 10 grams of methane daily. Pilot lights are found to be potentially significant contributors to inactive emissions. Similarly, measurements of combustion efficiency for operating appliances show a majority of values near zero but with small detected emissions for stovetops and water heaters that are also fit with gamma distributions. One exception is forced air furnaces, which were nearly all low emitters. The team also found that emissions from pilot lights likely constitute a significant fraction of inactive house emissions, and flames in dominant domestic water heaters when in steady operation.
Total emission estimates, 35.7 Giga gram methane per year, corresponds to 15 percent and 2 percent of the natural gas sector total methane emissions and state total methane emission, respectively, from the most recent state inventory for 2015. While methane emissions from houses are small compared to most other sources, California’s ambitious climate goals (for example, 80 percent reduction by 2050) suggest value in testing and repairing obvious leaks in residential gas lines, modernizing combustion appliances to move away from pilot lights, and gradually increasing the use of nonfossil energy sources for residential space and water heating and cooking.