My kids are tracked out of school for the next 3 weeks. We just built our pool with a 7ft spa. The kids are in the spa from 10am-6pm everyday. We have a 400k btu gas heater and keep it at 97 degrees when the kids are using the spa than turn it off when not in use. We figured previously that my heater will run $5/hr to run. My question is, how much of that 8hrs do you think my heater is actually running? the outside temp is 61 degrees. Anybody experience a similar scenerio and get an absurd gas bill. Part of me is thinking about adding a heat pump to my system and using the gas heater for very cold weather but I want to see how the pool is used when the novelty wears off (doubtful because my kids are 9,7,5 year old boys)