We have an 8' square CalSpa that is about 14 years old. We keep it set at 104 degrees and we have it in economy mode, which means it heats twice a day up to 104 degrees.
Our electric bill continued to increase so I put an ammeter on the tub to see how expensive it is to operate.
The tub is outside and we live near the coast in California. We will get frost during the winter, but other than that, the weather is pretty mild.
Our tub used 267 KWH per month during the winter. We're on a tiered electric system, so our cost for the top tier is $ 0.34. Our tub costs us $90.78 to operate. However, I think the average cost of electricity is more like $ 0.11. So it would cost $30 per month in any "normal" state.
Lee