Heating with electricity vs. gas?

Here in Seattle, we have some of the cheapest and cleanest electricity in the country (hydroelectric dams cause their share of environmental problems, but don’t produce greenhouse gases). This got us thinking about the common wisdom, which says that it’s more efficient to heat your home with natural gas than electricity. But does that still hold for the Pacific Northwest?

I started digging around for data (no surprise to anyone who knows me…) and was able to calculate the cost and greenhouse-gas emissions of these two heat sources. I quickly decided to limit the scope of the question to exclude comparisons of furnace efficiencies, and just focus on the costs and emissions of the energy that arrives at my house.

First step is to compare the measures of energy. Electricity usage is measured in kilowatt-hours (kWh). A watt is a measure of electricity flow (1 kilowatt = 1,000 watts), so a KWh is a thousand watts flowing for one hour, or a 100-watt lightbulb burning for ten hours.

Natural gas usage is measured in cubic feet (usually in units of 100 cubic feet, abbreviated CCF), but the energy content per cubic foot isn’t entirely constant, so utility companies conveniently report usage in therms. A therm is defined as 100,000 BTU, and is the same amount of energy as 29.3 kWh.

The cost comparison is fairly straightforward. Digging out some recent bills, we’re paying $1.0854 per therm, and $0.0506 per kWh. (these costs exclude fixed monthly service and line costs, but include taxes and other costs that are based on the amount of energy used). One therm’s worth of electricity (29.3 kWh) costs us $1.48 — 137% as much as natural gas, or a 29-cent savings per therm. In December, we used 86.35 therms of natural gas (for heat, hot water, stove/oven, etc), so it would have cost us about $25 more to use the same amount of electricity.

OK, so electricity costs about a third more. But what about the environmental side of things? I focused exclusively on greenhouse gases. Electricity comes from a mix of different sources, each producing different amounts of greenhouse gases. There’s also substantial losses in electricity distribution. Fortunately, the Union of Concerned Scientists has already compiled all these data, for each electricity-producing region in the country, as part of their report on the carbon costs of electric cars. If you dig into the technical appendix, here’s what you find about electricity in the Pacific Northwest:

Hydroelectric is indeed the largest source of electricity in the region: 47%. Other renewables account for 5% (1% biomass burning, and 4% from wind, solar, and geothermal — not separated out in the report). The other 47%, from nonrenewable sources, comes 30% from coal, 15% from natural gas, and 2% from nuclear. This adds up to a greenhouse-gas intensity of 451 g CO2-equivalent per kWh. (since some greenhouse gases have much stronger effects than others, this expresses how much CO2 they’re equivalent to)

It surprised me to learn that New England and California both have lower emissions per kWh. New England is 42% natural gas, 30% nuclear, 16% renewables, and only 12% coal. California is 53% natural gas, 15% nuclear, 23% renewables, and only 7% coal (plus 2% miscellaneous fossil fuels). Even though the PNW derives less of its electricity from fossil fuels, a much higher proportion of our fossil-fuel usage is coal, whereas New England and California both use predominantly natural gas. Yep, coal’s pretty dirty…

If you just look at the energy sources for Seattle City Light, our electricity is an impressive 90% hydroelectric. I’ve chosen not to focus at this small a scale, since electricity is bought and sold quite readily throughout the region. Using more electricity in Seattle would mean that we buy more electricity from other generators with lower amounts of hydropower. Also, trying to analyze things at this small scale would have to account for the fact that a hydropower dam’s output is pretty constant, so any changes would be to the other sources. I agree with the UCS’s regional classification as being the most meaningful scale of analysis for thinking about what the consequences would be if a number of people all changed our electricity uses.

Greenhouse-gas estimates for natural gas have recently been revised upwards, as new studies have quantified the methane emissions from natural gas wells. A report from the Worldwatch Institute comparing coal-fired and natural-gas fired electricity gives good emissions data for natural gas. Like the UCS electric-car report, this is a full life-cycle analysis; it takes into account the upstream emissions from producing natural gas, and transmission losses, as well as the emissions from burning natural gas in the home. Both of these are complete accountings, so they’re meaningful comparisons. Natural gas produces 7.23 kg CO2-equivalent per therm, according to this report.

One therm’s worth of electricity (29.3 kWh), by comparison, produces 13.2 kg CO2-equivalent — a whopping 183% as much as natural gas. Even here in the PNW, with over half our electricity from renewable sources, natural gas still produces substantially lower greenhouse-gas emissions. Natural gas looks like a clear win-win in terms of both greenhouse gases and financial costs.

Of course, money and greenhouse gases aren’t the only costs from energy use. Local and regional air pollution is another big one to take into account — and in some cities where the air is very stagnant, trapping pollutants and forming smog, it raises the question of “outsourcing” the air pollution to a remote electric power plant away from people instead of burning natural gas in areas with high population density.

If you’re in a city with a natural-gas electric power plant right in town (as was the case when I lived in Saint Paul, MN), I wonder how it would balance out: the power plant has much cleaner-burning equipment than your home furnace, but there are a lot more energy losses involved in converting natural gas to electricity and transmitting electricity from the plant to your house. If you decide to tackle that question, let me know!


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