Yes. The pool heaters operate on a timer and are set to come on in the morning and go off in the evening, therefore there will be some cooling off overnight when the air temperature drops. In the coldest winter months, heating the pool can be challenging with the water temperature dropping down overnight in the 30's and 40's. Unfortunately, under these circumstances, the pool heater may not be able to keep the water at 84 degrees. If the outside air drops below 55 degrees Fahrenheit, the heating pump may be unable to operate effectively, and failure of such devices is outside of our company's control and is regarded as an act of nature. Please note that cold weather does not constitute a mechanical failure, and no refunds will be given for problems that are due to cold weather.