I just installed a 24 foot round pool. It has an edge dept of a little under 4 feet and the middle is a little over 5 feet. I live in Upper Michigan where we can lose a lot of heat with cold nights and random cool days. I’m looking for a heater that would not take the entire day to heat up the water to a comfortable temperature. I want to turn it on in the morning for a bit so the kids can swim after lunch. What BTU would you suggest for this? We are looking for natural gas. thank you