The Terma Smart Split element probe is designed to work in combination with the VEO Range of Controllers to provide a fully functioning heating element. 650mm internal probe length. Wattage Selection: For correctly wattage look at output of radiator as c/heating in watts & choose element with closest wattage. Conversion;BTUS / 3.41 = Watts. The 1500w, 1800w & 2000w are powerful and shouldn't be longer than 70% of length of radiator. 1500w probe = 880mm = so the rad should be at least 1257mm in length; 1800w probe = 1015mm = so the rad should be at least 1450mm in length; 2000w probe = 1150mm = so the rad should be at least 1642mm in length. Electrification Advice: When electrifying any radiator check that model that it is suitable to work with a heating element. Dual Fuel Advice: If you are buying an element to convert a towel rail for use as dual fuel remember to regularly bleed the towel rail, as on a central heating system air can build up inside. A heating element should never be run in the open air as this could potentially cause the surface of the rail to get extremely hot and burn your towels.