Everyone should have a solar cover.  It’s inexpensive, easy to use, and it will pick you upfour to eight additional weeks of swimming – that depends on how you use the pool.  It conserves water by preventing evaporation.

Gas heaters are now available for around $1000.  That may seem to be a lot of money for a small above ground pool that normally heats up pretty quickly anyway.  An excellent alternative for a smaller pool is an active solar heater that works off your existing filter.  They’re around $500 to $1000, and the heat’s free!  Gas is faster, solar is very slow, particularly if it’s cloudy. 

Heat pumps are very efficient, but note that they don’t work as well when it’s cold out.  If you want to extend your season with a heat pump, choose one that was made for use in a colder climate.  It will have been engineered to be slightly less efficient when it’s 90°F out, but more efficient when it’s 65°F.