There are plenty of ways to heat your pool for pleasurable swimming through summer and beyond. One of the most attractive options is one of the various types of propane pool heaters.
One particularly good thing about these gas powered units is that they work really nicely in the outdoor setting by a pool. LPG (liquid propane gas) is quite economical, and easy and safe to store. It is also readily available.
Installing a gas heater for your pool allows it to do what it does best - heat quickly and efficiently. For this reason most of the heaters for the most demanding pool setting - that is above ground swimming pool heaters - use gas.
These out of the ground pools need more heat since they lose heat from the sides as well as from the top. (You can save money by insulating the sides properly, incidentally.)
When it comes to sizing swimming pool heaters, the other main loss to consider is evaporation from the water surface. (You can limit this in two ways - 1. cover the pool when it is not in use and the sun is not out and 2. put up a fence or some trees to act as a wind break, since wind increases evaporation significantly). If you have a hard to heat pool, then LPG is a good option to look into.