How much propane will I use

[Poolsean]

What is the worst case scenario that you can think of that you will need to heat up? In other words, how cold will the water be and what temperature will you want to get it up to?
You can calculate how many btu's needed for this temperature rise. Once you determine how many btus needed, you can calculate the costs.

Do you know what the cost of LP is?

[mmcguire]

I figure we will use the spa on average 8 hours per week throughout the year. Heating the pool every once in a while would be nice but I am really only concerned with heating the spa.

Will I need to run the heater the entire time we are in the spa? 4.5 gallons per hour looks expensive. We are able to get propane at $1.76 per gallon. I want to have a tank that is big enough that I will not need to fill it all of the time, will 125 gallons work or should I go bigger?