I just purchased a home near vero Beach, Florida. The home has a 17,000 gal pool and we've decided we need a heater to use the pool during the winter months. I am reluctant to start with a new one so we are looking at 2-3 year old used heat pumps. We have found a model HP21002 Hayward HeatPro but have some questions. I wonder if the 'armorcoil' exchanger is OK or whether I should keep looking until I find a unit with a titanium exchanger? What are your feelings about Hayward and this particular model? Our house is located on a lake so do you believe this BTU rating will be adequate? Lastly, I understand the COP for this model is 4.8 and I have seen other brands with COP ratings of 6.0 or higher, does this mean I will have a much higher cost of operation?