Dear Umbra,

When changing boilers for heating a house for the next 30 to 40 years, should we choose gas or electric? We have gas now and want to go from 80 percent efficient to 95 percent efficient. About 60 percent of our electricity comes from Missouri River hydro and 40 percent from coal. We have wind, but that is not developed, and will only be a small percentage in the future.

Chuck Berry
Brookings, S.D.

Dearest Chuck,

Good for you for wanting to improve your efficiency, and for knowing in such detail where your power comes from.

Summer is certainly the time to think about replacing your old heating system. It’s nice to be able to take the time you need to get bids from various contractors, research the most efficient boilers, drink some lemonade, and wonder whether winter truly exists. This year is a good year to do it, as well, because there are federal tax credits for certain very high-efficiency heating systems.

When considering boilers, think outside the walls.

Photo: iStockphoto

For the boiler itself, you’ll want to look at Annual Fuel Utilization Efficiency numbers and talk to reputable local contractors (AFUE is a measurement of the fuel used to heat the house vs. the amount that gets vented out — read about it and boiler shopping in another of my columns). In my area we can get contractor referrals from our gas company, so perhaps you can as well. Cost may make your decision for you. Electric boilers tend to be very efficient — they can have an AFUE of up to 100 percent — but heating with electricity can be expensive. Heat pumps are often recommended as an alternative to electric boilers. The highest AFUE I saw for a gas boiler was 95 (look at the U.S. Energy Star site for a downloadable list).

The question of choosing the fuel source for the new boiler is harder for me to answer. I won’t guess at the future status of Missouri River hydro, the upcoming presence of wind in the power mix, and what will happen with coal-fired electricity generation over the coming years. I do think natural gas will become more expensive and less plentiful as fossil-fuel prices rise and gas usage increases.

Let’s take a brief detour to look at how coal and gas stack up as sources of electricity (even though it’s not immediately relevant to your particular situation). Natural gas is cleaner than coal on all fronts. Coal emits 2,249 lbs of CO2 per MWh, while natural gas emits 1,135 lbs per MWh. Even at 40 percent of the mix, coal’s sulfur dioxide (future acid rain) and nitrogen oxide (future smog) emissions will remain higher per MWh over gas. In addition, we have the unknown amount of airborne mercury coming out of your coal plant. As for hydropower, it has not been known for its air emissions, until recent evaluations of the methane released by rotting plants under dammed and slowed rivers. I couldn’t find any numbers on the Missouri, however, so we’ll just have to vaguely consider it.

Hmm. I don’t like the look of your electric choice, and I’m supposed to be giving advice. What I think is that you’ll pencil out the costs, and won’t want to pay for electric heat. If price is a non-issue for whatever reason, see what you can find out about the coal plant producing your electricity. It may have a campaign against it, for example, so you can read all about that, or it may be honored as the country’s cleanest coal plant. Either way, I wager you can learn a bit more about the emissions specifics, and that will further tip the scales one way or the other.