Lets just say that it isn't as clear cut as Gasoline where you pay by the gallon and you know what you are getting. Fuel Oil is pretty straight forward as well. You get a liquid at a price per gallon. Thats it.

The trick with propane or LP is that the delivery is in liquid form, but the usage is in a gas form. The magic that converts the liquid into a gas occurs inside of the tank in which it is stored. A good analogy is that of boiling water. Water in the pan, steam (gas) is what escapes.

It is for this reason that any tank or storage device that stores LP can only be filled to 80% capacity, leveraging the 20% space as the gas area which is expelled through pipes into the system that will burn it.

In my case, the recommendation for the amount of LP I would need stored to supply my 400,000 BTU (British Thermal Unit) pool heater would be two 100 Gallon vertical tanks. This is what the propane company quoted me. It is also where I began to get confused.

First, I assumed that if I was getting a 100 Gallon tank then I would only be paying for 80 Gallons of LP, or 80% of the volume in the tank. After seeking out clarification, I discovered that they were referring to them at 100 Gallon tanks, but in reality they were 125 Gallon tanks. What they were quoting was the actual amount that they would fill the tanks with.

With a good understanding of that concept, I then went about looking at the tanks on-line which you can purchase yourself, rent or "borrow" depending on the propane company you deal with. This was when things began to go south again.

If you actually look for Propane Tanks on-line you will find that they are generally listed by Pound, not Gallon. So I was looking at 100 lb. Tanks that had no real representation of how much volume they actually contained in liquid form.

I decided that the whole tank issue was getting a bit complex and decided to simply determine roughly how much money I would expect to spend to heat my pool. At this point, I knew that I had a heater that was rated at 400,000 BTU that would burn 18.5 lbs. of propane in an hour to raise the temperature of my pool size of 20' x 40' (800 sq. ft.) by 1.25 degrees every hour. WHAT?!?!? I was back to pounds again instead of Gallons!

My frustration was due to the fact that I would be charged for propane by the Gallon, not pound! Why is it then that I couldn't get away from all references to propane in pounds? Google had to save me from this madness and quick. I was never that good in math and this was becoming insane.

Here are some of the random LP facts I discovered:

1. One Gallon of LP converted entirely to gas vapor is equal to 270 cubic feet. (Wonderful from liquid, to weight and now this!) Apparently when you are billed for propane it is itemized into cubic feet. That means that whatever your cubic foot number is, you have to divide it by 270 to discover how many gallons you actually utilized and thus are billed for at the market rate per gallon. 2. One Gallon of LP is also equal to 4.22 lbs. EUREKA!!!!! That was the magic number I needed to know!

The next step was to figure out the current ambient temperature of my unheated pool and then determine what my target temperature would be. Currently the pool is at 78F, thanks to my little Froggy thermometer floating in the pool. Ideally, I would like the temperature to be around 83F. With that, I fired up Apple's Numbers program (think Excel) and embarked on my math modeling exercise.

All of that just to get to this:

So as you can see, the best case scenario is if the summer is hot, warms the ambient water temperature so that I don't have to run the heater much. Besides, LP is as expensive as any other fuel source these days. Ouch!