I've Googled and found lots of information on formulas for how much it costs and how much propane to heat your pools, spas, etc. to a certain degree. This is our first pool so I have no idea how long we will need to run the heater daily to keep the pool/spa at a certain tempature, so these don't really help me. We need a gas company to come out and install a gas line and a tank and I need to figure out how much I would like them to fill the tank with initially as we are now very tight in our budget. We have a medium sized pool with spa. I only want to heat the spa, but there is spillover into the pool, so we will be loosing energy there. Since it gets pretty hot in NC, I only want to keep the spa around 99. I don't think we will have a cover on the pool during the summer, but can get a solar one if it really makes a big difference. Any clue how much I should start with to get us through just this pool season? 100 gal, 200 gal, 300 gal???