I just found this pool heater cost analysis program on the AquaCal website. I installed it and it works very well. Very detailed calculations although they seem to be tied to just a few brands of heaters. It looks like a heat pump is much cheaper than natural gas. It does pool volume calculations and includes local weather data by the half month. Very nice.
http://aquacal.com/index.php?option=com ... &Itemid=72
File Name: PoolAuditSetup.exe
Date: August 27, 2009
Download Size: 17.7 MB