Buy your heating oil and fill your tank on the very cold days. You pay for
your energy by the pound of fuel not the gallon. The energy of a lb of oil
is measured in BTU. The colder the oil the more it weighs (more dense) and
therefore the more lbs (BTU's) per tank. When the fuel warms up in your
tank (assuming it's inside the house) it will expand to account for the
change in density (function of temperature) but the number of pounds remains
the same. Obviously, assumes that the oil temperature in the delivery truck
is close to the ambient temperature. When the temperature is close to 10
below zero, as it was the other day, that would make about an 80F change in
oil temp after it reaches room temp. I'm guessing that the density change
is approximately 2% for a 50F change in temperature; so you'd save a grand
total of about $4.00 on a $200 fill up on a zero deg day.
Not much but it's fun to think about it. Hm-m-m-m same applies when filling
up you car gas tank <g>
The oil comes from very large tanks, and will be at the average ambiant
temperature, with averaging extending over very long time periods, on the
order of a month. It is colder, surely, in winter than in summer (fill your
tank in the winter, as if you had a choice). The oil does not spend enough
time in transit to your house to cool off appreciably. The oil delivered
when it is -20F is not likely to be any colder than the oil delivered two
days ago when it was +29, both are at something like the average temperature
for the month.
Your estimate of 2% is off as well, .1% is closer (based on vegetable oil--I
couldn't find data for petroleum).
Gasoline comes from underground tanks and is pretty much the same
temperature all year. In the winter this has no consequences but in summer
it may expand when it warms from 55 to 85 and overflow your gastank if you
insist on filling right to the top.
Assuming your hair brained idea has any merit, have you figured what it
costs you to heat that load of fuel back to room temp?
200 + gallons of cold fuel in your basment is going to make your furnace run
Going buy your assumptions, you would pay MORE on the cold days seeing
how the oil would weigh more. So... this means you would save money
filling up your tank on the warm days, and save even more if you fill up
your tank in the summer time when the oil prices are lower anyway <g>
From the ads I've seen in NY, fuel oil is sold by the galon. So, it would be
more dense in the winter. But, also more expensive. I'd suggest people fill
the tank in the summer, when it's cheaper. The percent or so more dense
won't do much difference.
Christopher A. Young
Jesus: The Reason for the Season
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