In May of 2007 my heating oil cost $2.50 per gallon.
In May of 2007 my electricity cost .071 cents per kilowatt. (This
number includes all the surcharges and distribution costs state and
local consumption costs, etc.)

There are 141,000 BTU's of heat per gallon of fuel oil. My heater is
80% efficient. This means that 20% of the oil I burn goes some place
other than into heating the air in my greenhouse. (20% of my oil
dollar goes someplace other than into heating the greenhouse air.)

There are 3412 BTU's of heat per kilowatt. A radiant heater without
fans is pretty much 100% efficient in converting electricity to heat.

My question is "How much heat can I buy for the air in my greenhouse
with $1.00 of oil versus $1.00 of electricity at the price of energy
in May 2007?"

My answer is
BTU's per oil dollar: 45120
BTU's per electric dollar: 48056

Scary stuff if my calculations are correct. Oil used to be the most
cost effective fuel for heating. In October of 1999, for example, my
oil cost .96 per gallon and electricity cost .064 cents per kilowatt.
The cost of one fuel is going up much faster than the other.

I cannot hope to generate sufficient BTUs with electricity to heat my
greenhouse this winter, (all my plugs are too small ;-P and I use an
average of 423,000,000 BTUs per winter above what the sun provides)
but if the fuel costs have not changed much this summer and my
calculations are real then it makes some sense to plug in some
electric radiant heaters to help out a bit. And the higher oil goes
in comparrison to electricty the more help those radient heaters can
offer.