Parasitic Libri GmbH Parasitic Thermosiphon Circulation in Closed-Loop Hydronic Systems

When a hydronic loop stops circulating, temperature gradients between heated and cooled zones (radiators, coils, piping routes) remain or emerge. Water naturally adopts vertical distribution based on density differences: warmer water (lower density) rises; cooler water (higher density) sinks. This spontaneous convection-without pump forcing-is thermosiphon circulation. In heating systems during the non-heating season: radiant floors or high-level radiators may remain warm from solar gain or residual heat. The circulating pump stops. Warmer water in the upper zones rises continuously through the piping network. Cooler water sinks back down, completing a convection loop. Energy loss mechanism: heat exits the warmer water via exposed pipe surfaces, radiators, or coil jackets. That cooled water then sinks, is reheated by the descending warm water column, and rises again. Each cycle involves some degree of irreversible loss to ambient.