Many homeowners with hydronic heating systems believe that turning off radiators in unused rooms saves energy. However, research from Europe and corroborating studies in the U.S. suggest that this practice can actually lead to increased heating demand and decreased efficiency. When a radiator is turned off, the room cools, causing nearby heated spaces to lose heat through walls and gaps. A study by independent researcher Nick Grant revealed that radiators in adjacent rooms worked 19-26% harder to compensate, resulting in only 3.3% to 5.4% energy savings overall. Additionally, turning off radiators can disrupt the efficiency of the entire hydronic system, causing boilers to operate at higher temperatures and longer durations, which is particularly detrimental for modern condensing boilers. Research from the Technical University of Denmark showed that this practice can lead to financial penalties for buildings due to inefficient heating. Experts recommend maintaining steady temperatures and using thermostatic radiator valves to optimize heating efficiency instead of turning radiators off completely.