On average, for an in ground spa, how long should it take to heat? It started at 76 degrees, it's been on for about an hour and is only at 79 degrees. It's a Raypak RP 2100 Digital, if that helps... I don't know how many gallons, it's just an average size. Also, just to humor myself, if I were to heat the pool too, how long would that take and what would the average bill be?