Below is a list of Water to Air Heat Exchangers manufacturers from St. Louis, Missouri. Water to air heat exchangers are devices used to transfer process heat from water into the air. Water is typically used in liquid to air heat exchangers because it is readily available and has excellent conductive properties; however liquids such as a water-glycol solution, steam, or a refrigerant may also be used. A refrigerant is a compound that undergoes a phase change from a gas to a liquid and back.