Hot Tub Thermal Creep

What is hot tub Thermal Creep?

No, it is not the unwelcome advances from a stranger in the tub.  It is a condition where the spa seems to overheat even though the set temperature is lower.

In the summer as temperatures soar, the ambient surrounding temperature around a spa can get warmer than the spa water set temperature.  Just as a lake, pool or any other body of water, the spa water will become warmer too.

Spas are usually built with energy-efficient components and systems that capture heat generated by the equipment, then transfer that heat back to the spa water. In warmer weather or when filter cycles are set to extended run times, “Thermal Creep” may occur.

What seems to happen is that the spa water gets hotter than the set temperature once the outside temperature gets hot. This condition is commonly referred to as “Thermal Creep” because of the gradual increase in the spa’s water temperature even when the heater is not on. 

Thermal Creep is a condition where the actual water temperature is higher than the set temperature.  Insulation in the spa and a well insulated cover can actually work against keeping the water cooler.

In any case be sure the filter cycle times are reduced and for those systems that have an AM or PM, be sure the filter cycle times do not overlap, perhaps causing an endless filtration cycle. Other control systems have a C or continuous mode for 2 speed pumps to cycle on low speed and that should be avoided as well.  For some spas with a small 24 hour circ pump, the heat generated by these smaller pumps is usually less. But if the spa circulates on the low speed of a 2-speed pump, it is best to reduce the filter cycle times.

Thermal Creep can cause Overheating

If the spa is in direct sun, perhaps an umbrella can shade the equipment side of the spa or any other form of shade.

Leave the air controls in the open position when the spa is not in use. - Vent your cover. Newer covers have removable center seal padding. To remove this padding, open the Velcro on one side of the vinyl pouch and slide the white padding out. - If your spa does not have removable center seal padding, you may instead place a folded cloth about ¾” (2cm) thick under all four corners of the cover before you lock it down. Opening the cover at night will also quickly cool the water down if desired. 

Reduce filter cycles to one hour each during the summer months. Remove some of the insulation if too close to pumps and equipment to help release internal heat and allow cooler air to flow around the equipment area. Reinstall Insulation in the fall months. 

Another person suggests filling up 2-4 empty gallon milk jugs with water and freezing them. Place them in your hot tub an hour or so before you want to use it. This will cool it down several degrees relatively quickly. After you are done, put them back in the freezer so they are ready for your next soak.

If there are any reflective surfaces right next to the spa such as glass or mirror, then perhaps they can be covered up to avoid amplifying the sun's heat towards the spa.