The TRV4 Classic is Class 1 rated for efficiency by the European valve manufacturers association making it one of the most energy efficient TRVs available.Available since 1993 and still Britain's best selling range of Thermostatic Radiator Valves Drayton's TRVs set the standards for design, performance and quality. The range includes Lockshield and Pushfit packs to suit most domestic and commercial heating systems.