Recently purchased a used spa ($100), and I wanted to do something a little different. I figured I already had all of the equipment with my pool so I decided to tie everything into it. I ripped up my wood deck, started forming for concrete, pulled up all of my pool equipment and ran 3 PVC pipes (drain, return, and blower) over to my existing pool lines. Poured my concrete slab and then started construction on partially submerging my spa. I then built a screened room around it tieing it into my existing pool cage. Here are some pictures... I would appreciate any comments on the pluses and negatives of doing something like this. It seems to be working fine for me as it is right now....

I am thinking of doing something very similar, but only for the purpose of using the solar collectors for supplemental heating and using the salt water chlorine generation my pool utilizes. The problems I have come up with and found solutions for are as follows: First, the pool pump is often single speed, and you aren't utilizing the full benefit of a spa. Solution is to be able to add a check valve in the return line from the pool pump to the spa and add an addtional pump to the spa. Another problem I have surmised is that most people want the spa to be hotter than the pool but with shared plumbing, it makes this virtually impossible. In order to have the spa hotter then the pool and still use the existing pool pump, you will need to invest in some Jandy type valves to isolate the pool when the spa is in operation, and visa-versa. These are not cheap.

Bar none, the simplest and most cost effective way to have the two are to keep them separate. Invest in the spa pack and away you go.

On the comments on your idea and design, I like the way it worked out for you. You put a lot of time preparing the surface for the spa, and it turned out well.