PU / PUW 1 / PUW 2 buffer tanks are inertial tanks for heating systems intended for the storage of hot technical water (not for sanitary use), necessary in all systems powered by a discontinuous energy source (e.g. solar panels, wood boiler, thermo-fireplace, etc.), or when it is necessary to increase the volume of water contained in the system (e.g. systems with heat pumps, cogenerators, biomass boilers, etc.).