Ice Bath Chiller Running Cost Calculator: Cost a Day

A chiller does not burn electricity because the water is cold; it burns it because heat keeps leaking in. Once the tub is down to temperature, the running cost is set by three things: how warm the air around the tub is, how well the walls and lid are insulated, and how efficient the chiller is. Enter your tub, your insulation and the numbers off your chiller's spec sheet, and this calculator works out the daily, monthly and yearly cost, plus how many hours a day the compressor actually runs. The key insight: on a thin, uninsulated tub, adding 25 mm of foam and a proper lid usually cuts the holding cost by far more than buying a more efficient chiller would.

How the calculation works

Holding the water cold is a heat-leak problem. The calculator works out the outside surface area of the tub (walls, floor and lid), then a heat-transfer coefficient for the walls from the foam thickness, using a conductivity of 0.025 W/m·K for rigid polyurethane-type foam plus the resistance of the still air layer on the outside. Multiply area by that coefficient and by the gap between air and water temperature and you get the watts of heat creeping in. Any pump running all day adds its full wattage on top, because almost all of a pump's power ends up as heat in the water.

The chiller has to pump that heat back out. Its efficiency is the ratio of cooling capacity to power draw, so a unit that removes 1,200 W of heat while drawing 600 W uses 1 kWh of electricity for every 2 kWh of heat it shifts. Dividing the daily heat load by the cooling capacity gives the hours the compressor runs each day. Each water change adds a one-off pull-down: cooling 1 litre by 1°C means removing about 1.16 Wh of heat, the same figure our chiller size calculator uses.

What the number leaves out

Treat the answer as the floor rather than the ceiling. It assumes the lid stays shut between plunges and the tub sits in shade. Direct sun on a dark lid, a lid left off for an hour, and your own body heat during each plunge all add load the formula cannot see. Leaky lid seals matter too, because cold water evaporating under a gap carries heat in with the moist air.

It also explains why chiller bills are seasonal. In a British winter the air around an outdoor tub is often close to, or below, the water temperature you want, so the compressor barely runs; the same setup on a warm summer night can cost several times as much. Run the calculator once with a winter average and once with a summer one to see your range. If the water change is the biggest line, the ice bath chlorine calculator can help you keep the water clean for longer between refills.