December 13, 2004

11:00 PM

How much oil is left in my 300 gallon underground home heating oil tank? I stuck the measuring stick in, and it came up wet from 15" on down. Assuming a standard, what is the general rule(r) of thumb?
posted by ValveAnnex to (7 comments total)

What is the shape and width/length of the tank?
posted by pemdasi at 11:53 PM on December 13, 2004

According to this website (scroll down) a typical 300 gallon underground storage tank has a diameter of 38 inches. So a dipstick reading of 15" would indicate the tank is about 39% full, i.e. 118 gallons. But on second thought you should subtract some due to the cylindrical shape...the volume drops more quickly than the height (math people, pls help.) So call it 90-100 gallons.

Tanks can vary in shape from a smooth cylinder, as you can see here. Still, the 300 gallon beauty on that page has a 42" height, so a guesstimate of 95 gal or so should be in the neighborhood.
posted by mono blanco at 12:01 AM on December 14, 2004

pemdasi: it's underground, in fact, under a stone patio. I can only assume there are known popular measurements.
posted by ValveAnnex at 12:08 AM on December 14, 2004

Why not fill it up, and then subtract the fill amount from 300?
posted by pjern at 1:11 AM on December 14, 2004

But on second thought you should subtract some due to the cylindrical shape...the volume drops more quickly than the height (math people, pls help.) So call it 90-100 gallons.

Because you are almost half way up the tank you can pretty much ignore the non linearity. Basically, 39% is a very good guess.

That said, if you normalize the radius to 1 the area of the filled part of the cross section is:

integral of { 2*sqrt(1-y^2) dy } from .21 to 1

Which is 1.16

1.16 divided by the area of a circle of radius 1 (pi) is .37

So, the correct answer is 37% full, or 111 gallons...
posted by Chuckles at 3:04 AM on December 14, 2004

Thanks, all. With oil prices, it's not possible to fill the tank. It looks like we can go another month or so. I appreciate the math, Chuckles. I'll call the tank 1/3 full and hope for the best.
posted by ValveAnnex at 11:09 AM on December 14, 2004

I housesat a place once that had oil heating and we ran into the problem of the tank having "gunk" in the bottom. We were told by the oil guy that over the years gunk (from the oil?) collects and settles in the tank. Anyway my point is that, depending on the age of the tank, it's possible that not all of that 15" is usable and/or oil.
posted by blueberry at 11:29 AM on December 16, 2004