I am building a pool in central Texas and our electrify is cheap .7, and we are on propane which is very expensive. I need the pool water warm for health rasons and was thinking I could use a heat pump to get the water warm, and then use an electric spa heater to get the spa hot. My builder does think the 11kw electric heater will not able to heat the pebble Tec spa, because it's not insulated well. Is this true? He wants to put a propane heater to heat he spa. Thanks for an input.