You might be a bit far North to extend the season with a heat pump. The temperatures tend to be a bit cooler on either end of the season, making the use of a heat pump lose its efficiency. They are great for keeping a pool warmer during the season though.

I would expect a gas fired heater to better meet your expectations. At 65 degrees, a heat pump will have lost a sizable chunk of the BTUs its rated for while a gas fired unit will have all of its.

Scott