Hi, we live in NH and have an 18,000 AG pool. We have used solar panels for the past few years, but they are just not getting enough sun. So I have finally convinced my hubby to purchase a heater. I am thinking something with a quick heat up for the weekends, but using the solar and cover to maintain the heat during the week. From what I remember reading a heat pump is slow and wouldn't work well with the colder Nh temps. So I need a gas or electric heater? Any brand or model suggestions? How many BTU's? Anything else I need to consider?