SAGE » Q&AQ: Given home heating choices of electric heat generated by a natural gas-fired power plant, propane, or wood burning in a woodstove (no live trees cut, all downed wood), which option creates the least total environmental damage?
Asked by Barbara James, '58, Carmel, Calif.
Woodstoves
Wood-burning technology has come a long way since the days of Ben Franklin, who invented the stand-alone stove in 1742. Back then, there was only one way to heat your home and that was with a smoky open fireplace. Franklin's efficient stove design became commonplace in American homes because it produced more heat while using less wood and making less smoke.
Any smoke that leaves a chimney is essentially wasted potential warmth, so when you make a stove more efficient, you also make it pollute less. According to the Department of Energy, an open fireplace is only 12 percent efficient. This means that more than 85 percent of the heat produced goes "up the chimney" along with copious amounts of smog-forming pollutants and particulate matter, contributing to respiratory problems such as asthma. As a result, the EPA began mandating, in the late 1980s, that all new woodstoves meet certain efficiency requirements. Conventional woodstoves, like Franklin's invention, have heating efficiencies in the range of 60 to 72 percent, while modern high-efficiency stoves can capture up to 80 percent of the wood's energy. These newer stoves are designed to encourage complete combustion, utilizing all of the potential energy before the smoke leaves the chimney.
My rural neighbors love not only the low carbon footprint of their woodstoves, but also the aesthetic of heating with wood. Woodstoves radiate heat from their massive cast-iron bodies as opposed to a furnace, which forces heated air into cold rooms. According to a number of Stanford energy consultants, your body actually feels warmer near a radiant heat source, meaning you can achieve higher comfort levels at lower room temperatures, conserving fuel and reducing emissions.
Despite the romance of wood heating, the smoke is harmful to our health, and the cleanest and most efficient stoves cost thousands of dollars. Heating with wood can also be impractical (and may be illegal) for many urban residents because of strict air quality regulations imposed by local air quality management districts.
For more on woodstoves, see the U.S. Department of Energy's "Wood and Pellet Heating: A Consumer's Guide to Energy Efficiency," and the U.S. Environmental Protection Agency's "Health Effects of Wood Smoke."
For more information about general air quality impacts, visit the Bay Area Air Quality Management District. There should be similar bodies in your area, too.
Electric heating
Unlike woodstoves or gas furnaces, electric heaters are nearly 100 percent efficient at turning electricity into heat. This might sound great, but the benefits are strictly local. The power plants that generate this electricity can be as low as 30 percent efficient, and just as dirty as any woodstove. Add the electricity lost with each extra mile of wire between the power plant and your home, and electrical heat leaves a comparatively large carbon footprint.
Once it is in your home, electricity is converted to heat through electrical resistance—more inefficiency, but this time intentional, as electricity passing through an inefficient conductor produces heat. Many energy consultants agree that heating an entire home using either electric baseboards or space heaters is like bathing with bottled water. Not only is it environmentally damaging, but it can be ludicrously expensive too, especially when you have options.
Electricity does have other home-heating uses, though. Heat pumps, for example, move warmth from natural hot spots in your attic or basement to regulate the temperature of your home using what would otherwise have become wasted heat. These pumps are expensive and they are not suitable for all climates. But they can lower your heating bills and your carbon footprint, especially if electricity is your only option. In many areas of the country, you can also lower the global impact of electric heating by purchasing renewable electricity from your utility. The Department of Energy maintains a database of providers who offer "green power" pricing, a voluntary premium to encourage green power investment. Although not a guarantee that "green electrons" will actually reach your home, they function as a signal to policy makers that the public is willing to pay extra for carbon-conscious generation.
For more on electric heating, see the DOE's "A Consumer's Guide to Energy Efficiency: Electric Resistance Heating," and "Carbon Dioxide Emissions from the Generation of Electric Power in the United States."
Fossil fuels
Fossil fuels including propane, natural gas and heating oil can be used to generate heat in your home through a forced-air furnace. Most of us don't have a choice as to which fuel source we use in our local area, but regardless, the carbon footprints of these fuels are relatively similar. On the annual fuel utilization efficiency (AFUE) scale, most new furnaces are around 80 AFUE and some can be up to 90 AFUE. Yet the furnace isn't the whole story. When the hot air leaves your furnace it sometimes is routed though cold places (outside, in a crawl space or basement, for example) and by the time the air reaches your bedroom, it can be sapped of 30 percent of its original heat content. Insulating both your furnace and its air ducts can make a huge difference, without the cost and complexity of replacing your furnace.
Cost breakdown
I did a quick cost comparison to illustrate differences in heating costs based on the average rates for my utility provider. The calculation for wood heating is low because clearly, your centrally located woodstove cannot possibly heat your whole home. The electric resistance heating costs might be higher than average because each home will require a different number of space heaters. The absolute numbers will vary depending on where you live, too—here in California we don't have to heat nearly as much as you would have to in Buffalo, N.Y., for example—but the rankings of least expensive to most should remain roughly the same.
| Gas @ $1.10/ therm |
Propane @ $2.25 gal |
Wood @ $200/ cord |
Electricity (resistance) @ $0.25/ Kw/hr |
Heat pump (air–air) @ $0.25 Kw/hr |
Heat pump (ground–air) @ $0.25 Kw/hr |
|
| $ per unit energy |
$1.37 | $3.06 | $1.32 | $7.50 | $4.72 | $2.50 |
|---|---|---|---|---|---|---|
| Average per year |
$70 | $157 | $67 | $386 | $243 | $128 |
What about no heat?
When I asked civil and environmental engineering professor Gil Masters which form of heating is best, he suggested "neither," since all choices have considerable environmental trade-offs. Does this mean forgoing a comfortable living and donning gloves and a sweater at the dining room table? Not necessarily. According to an article in the New York Times, architects in Germany have been designing houses that keep you warm and toasty throughout the year with virtually no outside energy inputs.
These homes, besides being extremely well insulated, take advantage of the nearly one kilowatt per square meter that comes streaming from the sun. One way you can do this in your home without ripping apart walls is to open blinds to let in daylight, then close them at night. Better yet, insulate these windows with quilts to prevent heat from leaving at night. Carefully inspect all doors and windows for leaks, and caulk those that you find. Even the most efficient heater will run up your bill (and carbon footprint) if outside air finds its way into your home. And if it is time to replace your windows, invest in double-paned glass, which prevents cold outdoor air from sapping your well-earned heat.
