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Posted by D Sherman [72.47.153.24] on Tuesday, February 14, 2012 at 21:28:30 :
In Reply to: OT heating a home? posted by bill in pa. [75.218.202.79] on Tuesday, February 14, 2012 at 20:56:42 :
Here are some rules of thumb that will get you close. Change the numbers as need be depending in your prices.
Gas is sold by the "therm", which is 100,000 BTUs worth. This accounts for pressure variations and for different gas compositions having different heating value. Currently gas is retailing for around $1 per therm.
Electricity is sold by the kWh. It takes about 30 kW-hrs to make 100,000 BTU, so at 10 cents/kWh, 1 therm in electricity will cost you about $3.
Oil is sold by the gallon. 1 gallon is good for about 140,000 BTUs, so at $3.60/gal, one therm in oil will cost you about $2.60.
So, oil is a little cheaper than electricity and way more expensive than gas.
Now figure in the efficiency of the furnace. Electricity is always 100% efficient. An old oil furnace might only be 60% efficient. A new gas furnace could be between 80% and 95% depending on how fancy it is. If we figure your oil furnace is 75% and a gas furnace is 90% (both towards the high side), then your effective cost for gas is 1/.9 = $1.11 per therm and for oil it's 2.70/.75 = $3.60/therm. It's just a coincidence that the inefficiency of an oil furnace happens to cancel out the "extra" BTUs in a gallon of oil, so that 1 gallon of oil roughly equals 1 therm in terms of heat delivered into the house.
That being the case, electricity at $0.10/kwH is a cheaper heat source than oil at $3.60, On the other hand, if your electricity is more then $0.12/kWh, you're better off sticking with oil for now. Also, since the costs per therm are so close between oil and electricity, the efficiency of the furnace might make the difference one way or the other.
I didn't work out an example for propane, but at 92,000 BTU/gal and $2.50/gal, you'd pay $2.72 per therm for propane.
When deciding whether to invest in a new furnace you have to speculate about how much the cost of each kind of fuel will go up in the future. Personally, if I lived in coal country like you do, I would burn coal. At $50/ton and 12,000 BTU/lb, it works out to well under 50 cents/therm even figuring a furnace efficiency of only 50%.
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