We are the Poolside Cabana With Gourmet Flair. Our pool is solar hot water heated – pool water is pumped to black coils on the roof, gets solar heated and then pumped back into the pool. We can keep pool temp between 80 and 92 year around.
We certainly do NOT charge to “heat the pool”. IMHO that’s really tacky-cheap. Either it’s heated, or it’s not. Heating the pool is a cost of doing business for your listing.
My understanding is that even with an electric pool heater it would take a LOT of time to heat thousands of gallons of water even a few degrees, hardly worth the effort to turn the heater on/off. BTW 85F is the recommended “ideal” temp, not 87F.
Most people I know with heated pools leave them heated year round, and use a cover to help retain the heat during the cooler parts of the year (as do we). A good electric heater can be set for a variety of heating arrangements depending on the volume of your pool and your day/night temperature fluctuations.