We did a test and found that after two-three hours, the water temperature had risen to 40 °C. We have not yet got an opportunity to put it in freezing weather. The beginning water temperature appears to have a greater impact on the heating time than the air temperature.Our guess is that it will take around 3 hours to heat up a tub filled with water 5℃ and air temperature -10 ℃. Stop adding wood to the fire or switch off the switch when the water temperature arrives at 40°C and let the burning coals keep the temperature. With the help of the remaining hot coals, you should be able to stay in the 38°C–40°C range for at least one hour. Temperatures between 35 °C and 40 °C are ideal for me, and it’s simple to maintain this range with minimum monitoring. All of the materials still work well at 20°C. Temperatures as low as-50 °C can be tolerated by camlock fittings and stainless steel coil. The tub’s vinyl tarpaulin material can endure temperatures as low as -30 °C before it becomes brittle and breaks down.