There are a lot of variables that determine monthly operating costs. Some of these variables include climate, bather load (how often the spa is used), filtration cycles, cost per kilowatt hour in the area, is it a 110v or 220v system and whether or not the spa is foam filled or recovers the waste heat off of the motors.
As you can see there are many factors in determining your monthly costs. Most spas monthly costs are about a dollar a day which is pretty reasonable considering the benefits. Now, if you can recover the heat produced by the motors to heat the water is that going to cost less? It’s certainly not going to cost more, is it?
The dollar a day figure is based on using the spa 30 minutes a day, 5 days a week in a cold Canadian climate.