A Solar Forced Circulation Water Heater, also called Active Solar Thermal system requires a pump to provide circulation of the fluid. Usually needed when there is not enough space on the roof, where the Central Hot Water Tank is placed in the lower levels of the building. A forced circulation solar system is a solar thermal installation in which water circulates within the circuit driven by a pump. FDA, REACH,CE, RoHS, ISO9001 certificated (3. 0 GPM) Shop products from small business brands sold in Amazon's store. Discover more about the small businesses. What is a forced circulation system? Forced circulation solar thermal systems use a pump to circulate the heat transfer fluid between the solar collectors and the storage tank, ensuring greater efficiency even in the presence of distant installations or in complex environmental conditions. By utilizing solar energy with the help of mechanical circulation (pumps), this system.