How to compare heat sources for savings, now

November 11, 2006 | By | 1 Reply More

Okay, so we all would like to save the planet, save the environment, and save a buck on heating and cooling.
The price of heating gas is rising. So, how can I decide whether electric heaters are more cost effective than the gas furnace? How do I compare gas company therms to electric company kilowatt-hours?

Easy! One therm is 29.3 kilowatt-hours. But, how much heat is that? Well, a kilowatt-hour gives you 3,413 btu’s. It doesn’t matter if you use these kwh’s in a space heater, a TV, a lamp, a fridge, or a ceiling fan. All the kwh’s you use in the house become heat in your home. Every one! Nearly perfect efficiency.

How do you convert therms to btu’s? A therm of gas is defined as 100,000 btu’s, but it is actually a bit trickier to figure in practice. If the gas burns with complete efficiency, and all the heat is kept in the house (as in a gas oven or ventless fireplace log), this definition useful.

But in gas central heating, about 20% of the heat goes straight up the flue! Then you also have to figure in the kilowatts you use to blow the air around. Those contribute some heat, but add to the actual cost of heating.

From my last utility bills:

  • Gas: $1.65/therm / .80 (80% efficient furnace) gives me $2.00/100,000 btu’s
  • Electric:$0.06/kwH x 29.3 (kwh/therm) gives me $1.75/100,000 btu’s

So, although a $1.65 therm is cheaper than 29.3 khw at $1.76, keeping the overall house cooler and using space heaters where needed will probably save me some money this winter.

Even if I had 94% efficient gas furnace (they make those for a few thousand dollars), gas would barely break even with electric only until the gas prices go up. They will. Electrically, I live over a big coal bed and only 100 miles from a working nuclear power plant, so I expect those rates to stay pretty stable.

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Category: Economy, Energy, Environment

About the Author ()

A convoluted mind behind a curly face. A regular traveler, a science buff, and first generation American. Graying of hair, yet still verdant of mind. Lives in South St. Louis City. See his personal website for (too much) more.

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  1. Dan Klarmann says:

    Update 5 years later: Gas (Laclede) costs $1.29575 for the first 30
    therms and $0.68407 for each additional therm.
    Electric (AmerenUE October) is $0.089/kwh

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