I have a inground spa attached to pool. It has its own main drain and 3 jets. It has a short wall dividing it from the pool. So water from the pool spills into the spa. In front of pump there are 3 valves: Pool main drain, pool skimmer and spa main drain. In order to heat the water, should I close the 2 pool valves and open the spa main drain valve? It seems to make the pump work harder when I do that, but I'm trying to heat spa as fast as possible. The spa is about 400 gallons. I also want to know how long it should take to heat up.