One other benefit of the volumizer: energy storage for defrosting. My volumizer is in the return path and upon a defrost cycle, the energy for defrosting comes from this volumizer first and then the radiators. Higher system volume will lead to better defrost performance and less cooling of the radiators during the defrost. I also have a bypass valve between flow and return that is set to a high differential pressure so that it is never open in normal operation. This winter I plan on testing whether closing all radiator thermostats during a defrost will allow to use just the volumizer water only for defrosting. When all TRVs are closed, the differential.pressure should be high enough for the bypass valve to allow flow.