I'm putting in a pool and spa and am debating if I need a separate pump for the spa. One builder tells me I need 2 pumps, but concedes it is mostly for convienance. The main pool pump can run to circulate and heat the spa using floor returns. Then if I want jets, the air switch kicks in the second pump. However, my wife and I don't really like the powerful jets all that much and tend to try and sit between the outlets. I'm leaning toward a single pump (1.5 hp sized for pool) because I think that will provide more than enough force to the 4 spa jets. The only thing I think I loose is the ability to turn it off remotely at the spa using an air switch since it will be the only pump and hooked to the timer.
Anything I'm not considering? The second pump, air switch, extra piping, and added electrical service required will cost an extra $1000.