In Blue America, electricity is in and natural gas is out. The movement to ban natural gas service in new construction started in Berkeley, California in 2019 and has spread to other localities including New York City. The rationale is that burning natural gas has CO₂ emissions. The unstated implication is that electricity does not.

But the largest single source of electricity in the Unites States is natural gas combustion. In 2021, 38 percent of electricity came from generators powered by natural gas. So, currently the choice is not between electricity and natural gas, but between the use of natural gas directly in the home and use as a fuel at an electric generation facility. Banning natural gas use in the home only makes sense if increasing home electricity use burns less natural gas, and thus emits less CO₂.

Natural gas is used to generate electricity using three technologies. The first makes steam that is used to spin a turbine that drives a generator that makes electricity. The second burns natural gas to spin a turbine directly like a jet engine that then drives a generator. The third, which is a combination of the first two technologies (and is called combined cycle), burns natural gas to spin a turbine directly and also captures the waste heat to make steam and spin another turbine that drives a generator.

Electricity generation is not 100 percent efficient. Thus the energy content of electricity produced through natural gas combustion is less than the energy content of the natural gas used in generation.[1] The heat rate of an electricity generator is the amount of energy used to generate one kilowatt hour (kWh) of electricity. The ratio of the heat content of electricity (3412 British Thermal Units (BTUs) per kWh) to the heat rate of a generator measures the heat lost during the generation process. In 2021 the heat rates in BTUs of natural gas used to generate one kWh of electricity in the U.S. ranged from a high of 11,068 for turbines to 7,580 for combined cycle. Thus, less than a third (3412/11068 or 31 percent) of the natural gas heat content is available from electricity generated from turbines and 45 percent (3412/7580) from combined cycle. And in states such as California, the ironic effect of the use of solar generation is a shift in the composition of natural gas generation away from more efficient combined cycle towards less efficient turbines because of the need to rapidly increase generation at sunset, which is not possible with combined cycle generation.

Any discussion of the CO₂ emissions reduction arising from mandating conversion of end uses to electricity must consider the heat lost during electricity generation. For conventional electric stoves, dryers, hot water heaters, and heating, the heat loss is large. The available heat for use in the home is limited by the heat content of electricity, which is less than half of the heat content of the natural gas used to generate it. Thus, natural gas is used in far greater amounts through electricity generation than would be used if it were burned in residences for those uses.

For heat pumps the calculations are more complicated because they use electricity to “move” heat rather than electric resistance to produce heat and thus can produce more available heat than the heat content of the electricity used to operate the heat pump. For example if you burn 100,000 BTU of natural gas in an efficient (41 percent of all 2021 furnace sales) residential furnace you get 95,000 BTU of heat delivered to the house. If you use 100,000 BTU of electricity in a heat pump you get 200,000 to 300,000 BTU of heat in the house.

So, it is certainly possible for heat pumps to make up for the heat lost using natural gas to generate electricity. The Coefficient of Performance (COP) is the ratio of heat pump output to electricity input both measured in BTUs. Given the heat losses I calculated earlier for the use of natural gas in electricity generation, it is possible to calculate the breakeven COPs. When electricity is produced using gas turbines with 69 percent heat loss in the generation process, compared to 5 percent lost in efficient home natural gas furnaces, COPs would have to be 3.1 (i.e., (1-.05)/(1-.69)) to make up for the generation heat loss. When electricity is produced with the more efficient combined cycle technology (55 percent heat loss in generation), COPs would have to be only 2.1 (i.e., (1-.05)/(1-.55)) to break even.

The heating efficiency of heat pumps is measured by the heating seasonal performance factor (HSPF), which can be converted to COP through a simple formula.[2] To achieve a U.S. Department of Energy energy-star rating for efficiency, the HSPF must be above 8.5 or a COP of 2.49. So, with combined cycle natural gas production of electricity, energy star rated heat pumps would break even and offset the heat losses during electricity generation. 39 percent of heat pumps sold in the U.S. in 2021 had the required HSPF rating.[3]

The calculations also are more complicated in a comparison of electric induction stoves versus natural gas stoves. Most of the heat (about 84.5 percent) available in the electricity used to operate induction cooktops is transferred to pots used and the food within them (Table 4 here). In contrast only about a third (31.9 percent) of the heat available in natural gas is transferred to the cooking utensils and food. The rest simply heats the air. When electricity is produced using gas turbines with 69 percent heat loss in the generation process, an induction stove with 84.5 percent efficiency results (.31 X .845) in 26 percent of the original heat available delivered to heat food. When combined cycle generators are used (.45 X .845) 38 percent of the original heat available is delivered to heat food. Thus, depending on the natural gas technology used to generate electricity, induction electric stoves use slightly more or less natural gas to heat food than burning natural gas directly in the home. And natural gas used for cooking is a trivial component of residential gas use.[4]

As long as natural gas is used to generate electricity, bans on natural gas use in new residential construction result in reductions in CO₂ emissions only if very high efficiency heat pumps are used and only if combined cycle rather than simple gas turbines are used for generation. All other uses of electricity actually increase emissions because of the heat losses in electricity generation. So why are localities in Blue America banning natural gas?