Hi Robert,
I’m the author of the original post and what you want to do sounds perfectly normal to me. It’s exactly what I’m doing and is a classic use of a pool HEAT PUMP as opposed to a straight HEATER.
Are your pool guys definitely talking about a heat pump?
My pool is much smaller than yours (~8000 gallons) but it operates exactly as you suggest. I only power the heat pump using solar (i.e. during the day) and the most it can add is about 6 degrees a day. It then loses about 3-5 degrees overnight depending upon the weather.
So I can slowly get it to a temperature and keep it there for days on end when the weather is good. Melbourne gets pretty cold in the winter so I shut it down. But it sounds like Phoenix climate would allow you to run it year round with the right sized pump.
The crucial thing is what size heat pump to get. I’m in Australia so all my research used metric units of litres and kilowatts. This is an Australian website for one of the major pool suppliers here but has a useful calculation that came out about right for me ( pool size litres / 2500 ). It suggests 14kw for me and I got 15kw which works well.
Maybe you could use this to get a very rough idea of size required, in KW, convert to BTUs and see if that’s anywhere near what your pool guys are suggesting.
The other tip is to get a good thermal pool cover if you don’t have one already and cover the pool every night when needed. It made a massive difference. Probably halved the losses overnight.
You’re right about the electrical supply. I had to have a qualified electrician install it and add a dedicated sub panel etc.
Hope it goes well.