You might not understand that simple math yourself.
Your furnace may cost $2.18 per hour but that is actual burner run
time. Most furnaces dont run for an hour each hour. Way less actually.
Your single electric heater however probably will run a solid hour and
more. Your oil furnace is heating your entire home. Your electric
heater is heating a single spot in that home. Add up the amount of
electric heaters you need to put out the same amount of heat as your
oil furnace. Now add all of those $0.12 per hour electric heaters.
It all depends on how many heaters but the numbers will be a bit
closer now than in your example of "simple math".
Bubba

I used 228.10 gallons of fuel oil for last years heating season of ~5
months. This is on average 1.5 gallons of fuel oil per day. Understand
some days I don't run the furnace, but lets just say on average to
keep the math simple, thats approximately $5.00/day at today fuel oil
price. As a comment to a previous post

"You'll probably find the space heater very expensive to operate."

All I was trying to prove is that Oil Filled Electric Heaters cost
$0.12/hr to operate and this might prove more cost effective to the
original poster's problem. And yes it is rooted in simple math. I use
one in the family room and keep the rest of the house closed up and
much cooler. Mine does cycle and I don't leave it on 24/7. So in my
humble opinion, for some applications, oil filled electric heaters
offer a cost effective efficient alternative.