Manual radiator valves and thermostatic radiator valves (TRVs) serve different purposes in regulating a radiator's heat output. Manual valves require physical adjustments to control the flow of hot water into the radiator, operating on a basic on/off mechanism or allowing for manual modulation of heat output. In contrast, TRVs automatically adjust this flow based on the ambient room temperature to maintain a desired level of warmth, improving energy efficiency and comfort without the need for manual intervention. While manual valves offer straightforward, user-controlled operation, TRVs provide a more sophisticated, self-regulating heating solution that can lead to energy savings by automatically reducing heat output once the room reaches the set temperature.