Indirect fired water heaters are used for low temperature types of supply water heating applications requiring temperatures up to 190F. These are also used for combination closed system/supply water heating applications. It is an industrial quality unit designed for economically heating large volumes of domestic or process water for commercial and industrial applications. The all bronze and copper heat transfer coil eliminates the possibility of rust throughout the water passages. The indirect principle of heating the process water with sealed-in primary water combined with controlled circulation minimizes the possibility of scaling within the heat transfer coil for low or high temperature applications.