Field guide to home
heat, cold & soak
Tubs & Saunas
Worksheet / 03
Energy math
03
Operating-cost worksheet

What does the ritual cost to run?

Use equipment power and expected runtime for a simple upper-bound energy estimate. Then refine it with measured usage when you have it.

InputsAnnualized
Example: a 6 kW traditional sauna heater.
EstimateFull-load model
Estimated electricity spend
—
per year at the selected planning rate
Monthly average—
Annual kWh at full load—
Electricity rate used—
FormulakW × hours × uses
Planning estimate only. Heating/chilling cycles, ambient temperature, insulation, covers and standby behavior can materially change actual consumption.
Notes from the worksheet

How to tighten the estimate.

Use the manufacturer's rated wattage or heater kW, then model how long the equipment is actually energized. A sauna heater may cycle after reaching temperature. A cold-plunge chiller and a hot tub run intermittently rather than at nameplate draw every minute of the year.

For a sauna

Include warm-up time plus the session itself. For a conservative upper bound, use full rated power for the entire period.

For a cold plunge or hot tub

Continuous-duty equipment is better modeled from measured daily kWh when available. Manufacturer energy data or a plug-in energy meter can produce a tighter estimate than nameplate power alone.