I currently have a two pump system:
1 - Hayward 2 speed 2HP pump that handles circulation of the pool and spa; intakes from the pool and spa come into this pump, go through the filter and heater, then are split back out to pool and two lower jets in the spa via a jandy three proportioning valve.
1 - Hayward 2HP pump (maybe 2 speed, but it's wired to a switch so only runs on high) that has an intake from the same plumbing circuit as the spa intake going to the first pump (i.e., the spa has two drains in the bottom of it, both pumps tie to both of these drains), but the output is to 6 or 8 jets in the upper portion of the spa. This pump does not tie into the filtration or heating system, only recirculates water in the spa.
To get the spa to blow out of all of the jets today, you have to run both pumps. Because they're tied together at the drain, this can cause one pump to rob the other and cause it to slowly lose prime (pump dynamics would explain that two pumps that share an inlet but one has more outlets will move more water than the other, which will rob the pump with less outlets of water). To overcome this, we have either made sure to run only one pump at a time (heat the water with the main pump then turn off and recirc with the second pump) or draw a little bit of cold water from the pool to supply the main pump with enough water to not lose prime, which makes heating inefficient, but it works.
Our main pump is now leaking some water (I've replaced the seal once before but the thing is over 15 years old) and I'm thinking it's a great time to look at newer pumps. When I do this, I'm thinking of replacing both 2hp pumps with a single 3hp VSP instead, and re-plumb things so that I can have one pump do it all. I'm thinking of the 3hp so that when I want to run the spa I can crank it up and get stronger flow to the jets that hit your back, but run it fairly low the rest of the time. This would also give me the benefit of having all of the jets in the pool flow through the heater, which I would think would make the heater more efficient as it would distribute warm water from more places in the spa.
I'm not really concerned that much about electrical cost (power is cheap here in Louisiana), but I suppose it's a plus. What do you guys think about this idea? Any alternatives come to mind? If I go VSP, what is the general consensus on make/model?