This the temperature of the Solar Hot Tub, the actual water in the hot tub. This is heated with the new www.SolarHotTub.com kit which features a 80 to 120 gallon solar storage tank and a heat exchange system to keep the hot tub at temp. The 80 square feet of solar thermal panels are flat-plate frame copper with flanges framed and insulated. The pump station handles either water or glycol as the heat-transfer fluid. This is a great great great Solar Hot Tub System. WOW.