This may sound crazy, but has anyone installed both a heat pump and a propane heater to heat their pool? We live in Ontario, Canada, and will be installing a 20X40 rectangular inground vinyl pool with an 8ft deep end. We are planning on installing a Titan IV heat pump, for it will be the most cost effective mode to heat the pool, and will use a solar blanket to help retain heat at night. From what I've learned (from this excellent site), is that heat pumps are slow to heat but once you reach your ideal temp they can maintain it at a decent cost. As for propane heaters, they can reach your ideal temperature very quickly but will cost alot in propane to maintain that temperature.
So I was wondering why not use both systems? Why not use the propane heater to quickly reach the desired temperature and then have the heat pump maintain it? Especially in the early summer & early fall months when the temperature in the air can drop quite low and cool the pool off.
Does this make sense??