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I dont' have any meter proof, but generally you can save money by doing this. People set back their home thermostats all the time to save money. It's all a matter of how long the heater runs to heat the water to operating temperature, vs how long it would have run to maintain the water temperature during the same time period. If your heater consumes 5,000 watts, and your electric rate is $.07 per kwh, it costs about $0.35 per hour to run the heater. If it takes 5 hours to heat the water, it will cost about $1.75 to heat the spa water once per week. The spa will also consume power that week for filtering, and for whatever the heater needs to keep the water at 72.If the heater needs to run more than 5 hours per week to keep the water at 102, then your friend may be saving money.I just keep my water at full temperature all the time. I've heard that certain spa chemical routines may not function as intended at low water temperatures.Brewman