A heating coil for an air handler is a device used to transfer heat from one medium to another. It is commonly used in air conditioning systems to heat air before it is circulated through the building. The heating coil consists of a series of metal tubes that are connected to a heat source, such as a furnace or boiler. The tubes are filled with a heat transfer fluid, such as water or glycol, which absorbs heat from the heat source and transfers it to the air passing through the coil. The heated air is then circulated through the building to provide a comfortable indoor environment. Heating coils are also used in other applications, such as water heating and industrial processes. They are an efficient and cost-effective way to transfer heat from one medium to another.