Lower heating demands for space heating impose new requirements for the operation of radiators. Contemporary type of new building construction, retrofitted buildings with smaller heat losses and higher requirements for energy efficiency and thermal comfort, demand an improved radiator design and regulation of heat output. As heating systems mostly operate at part loads, it is important to adopt the heat output as quickly as possible to the variable conditions. This paper presents an experimental validation of an improved heat output regulation concept for multi-panel radiators. A novel concept of water flow arrangement for double panel radiators was investigated. The proposed design enables different sequential water flows through each parallel connected panel. The experimental analysis was carried out in two steps: first, the heat output was studied in a nominal steady state at standard testing conditions; second, the radiator was tested at transient conditions. The results show that the implementation of the modified water flow arrangement significantly improves the transient response of heating radiators in terms of reduced time delay and balancing time. An improvement of the regulation ability, expressed as controllability, was also identified. (C) 2018 Elsevier Ltd. All rights reserved.