# Heat water with hot air

Problem: Use excess exhaust air heat from industry to heat outdoor pool. What temperature and at what pressure would air have to be to heat volume of water, say 375 m3 to 25 °C. Is there a way of calculating a smaller volume, then scaling it up?

• The physics involved in this question might be better addressed in physics.stackexchange.com . It would also help if you knew the temperature and volume of the exhaust air, as that will make a difference. Another significant factor for the amount of heat required to sustain the pool at 25 degs is the ongoing heat loss from the pool, which will differ depending on ambient temperature, humidity, and wind speed, as well as the size of the pool (more surface area = more heat loss to evaporation). Without those thing defined, you can't get an exact answer. Jan 26, 2022 at 4:13
• Mechanical engineers who deal with heat exchange can deal with this. Whether what you want to achieve is possible with also be dependent on: the temperature of the exhaust air, the temperature you would like the pool water to be, the distance between the heated air & the pool - how long do the heating pipes have to be, diameter of the pipes, available insulation for the pipes & its heat retaining, the properties, the production rate of heated air (cubic meters per hour), humidity of the heated air, what will be the heat transfer medium: air, water or refrigerant.
– Fred
Jan 26, 2022 at 22:57
• Thank you, I'll have to measure the volume of air and temperature of air that is coming off from the exhaust gas. The surface area would me 250m² at a maximum. The temperature of the water would be able to fluctuate between 22deg & 28. The next problem is to work out what mechanical process to use to getting the air to heat water... Jan 27, 2022 at 12:31
• As @blacksmith37 notes, the source of the exhaust is important - can you provide that? Corrosion can be incredibly fast if acidic liquids condense on the heat exchanger.
– Mark
Jan 27, 2022 at 22:20
• Having just thought about this, the best way to get warm/hot air to heat water is to direct the air into pipes, duct or flue & to submerge the pipes, duct or flue in the water. However, do not exhaust the into the water in case the hot air contains something that could contaminate the water. Let the end of the flue emerge from the water so the cooled air can exhaust to the atmosphere.
– Fred
Jun 26, 2022 at 19:26