I really can't give you much information except to say I am in the process of installing a 21002 into my existng pool. For me the task is a little troublesome because the installer of my pool 12 years ago did a bunch of weird conversions with the pipe system. He installed part hayward and part pentair products, this I think has caused problems for me. Staying with 1 manufacturer is probably a good idea. I would also suggest making sure everything is "standard" and as designed by the factory. As far as the 3100 is concerned I guess it depends on whether you will need to cool your water. Are you in a very warm climate? The one added feature I went for was the dual thermostat so if I add a hot tub in the future the heat pump will be ready for it. I had never heard of a 6 foot deep inground pool. Is that deep enough?
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