Everything is possible here at Poolheatpumps.com. For your size pool I would like to see you with a heater over 100,000 BTU's. You need that so that the spa doesn't take forever to heat up and also since you have a water fall you need a big heater as that sucks the heat right out of a pool and can double your heating bill as the fall causes water to evaporate and evaporation is pure heat loss. Think about water boiling on the stove. It is cooling the water so that it doesn't get above 212 degrees at sea level. I like that idea of using gas in the winter for the spa and then using the heat pump in the warm season from May first to October first. This year some of my customers had their pool up to 85 degrees in mid April in Maryland. I would like to make the heat pump work all that it can and then use the gas when it gets too cold for the heat pump and then you will have the lowest operating cost possible. So get a big heater by a big company that has been around for over 20 years with a long warranty and you will be fine. All my favorites are on the site. Jandy, Heat Siphon, Rheem, Gulfstream, Hayward etc. I like to promote the heaters and companies that I love who are doing everything right. I hope that helps.