December 28, 2010 - a history of heating my house, and current economics

In the wake of yesterday's blizzard, I've been thinking about how we heat our homes.  At over 150 years old, my house has kept people dry and warm for quite some time.  Much of the house remains the same as it was originally, while other "new" systems like electricity and running water have been installed later in the house's history.  Its heating systems have likely been changed several times in those years.

[Photo: down by the docks on Monhegan Island, Maine.  A large cache of propane tanks rests just out of view on the right.  Propane provides a major part of Monhegan's space heating energy needs.]

When the house was built, its residents likely burned wood to keep warm.  The front room or parlor on the first floor had a fireplace, as did the bedroom above the parlor.   (These fireplaces are now bricked up, as the chimney they used is now dedicated to an oil furnace situated in the basement.)  Until 1885, wood was the dominant fuel used to heat homes in the U.S.  After 1885, wood was surpassed by coal as the dominant heating fuel in the U.S.  It isn't clear whether my house was ever heated by coal.

Today, my house has three primary heating systems: an oil furnace in the basement that feeds warm air to the first floor, a propane "decorative appliance" in the kitchen, and small amounts of electric heat (a baseboard in one room, and a portable heater).  How much does it cost for me to operate these resources?  How are my decisions affected by that cost structure?  What should I do differently?

A few data points:

The portable electric heater is rated at 1,500 W.  In one hour, it uses 1.5 kWh.  One kWh = 3,412 Btu.  Thus in one hour of maximal operation, the heater puts out 5,118 Btu of heat.  Over the past several years, I've paid an average of 15.5 cents per kWh delivered.  This means the portable electric heater costs 23.25 cents per hour of operation -- or yields 146 Btu per penny.

According to the Maine Office of Energy Independence and Security, oil in Maine is retailing for an average price of $2.98 per gallon as of 12/20/2010.  In general, a gallon of heating oil contains about 138,690 Btu.  This divides out to 465 Btu per penny assuming 100% efficiency - or 386 Btu per penny at a more realistic 83% efficiency.

The Maine OEIS reports that the statewide average for propane based on a use of 925 gallons a year is $2.74 per gallon.  Notably, a gallon of propane contains less usable energy than does a gallon of oil; a gallon of propane might contain 91,330 Btu.  This divides out to 333 Btu per penny assuming 100% efficiency.  Even assuming 80% efficiency, this yields 266 Btu per penny.

Compare wood, a fuel the house is no longer set up to burn.  Wood can be an imprecise fuel type, with great variability in both how much wood is really in a delivered cord, as well as in how many Btu are available per cord.  (It's supposed to be 128 cubic feet per cord, but in practice air spaces mean there is almost never that much wood in a cord.)  The EIA recommends a figure of 20,000,000 Btu per cord.  Prices vary widely, but $200 per cord isn't a bad price in Maine.  Using that figure, you get 1000 Btu per penny assuming 100% efficiency, or 800 Btu per penny at a more reasonable 80% efficiency.  This makes wood seem like an attractive option.

Btu per penny may not be the only factor I consider in allocating my heating burden across these fuel sources.  For example, I can set the portable electric heater up anywhere in the house, while the oil-based warm air system is permanently installed in the first floor of the house.  Wood may appear economical, but without further capital investment (in a wood stove) is unavailable as a heating source.  Still, this look at the history of the house is illustrative.  What did previous owners spend on heating?  What fuels did they use?  Do we pay more today to heat our house than they did in 1860?  Are we more comfortable today than was the house's first owner?