I've built a controller similar to Garfield's because most if not all the $17-$35 all-in-one controllers max out at 1000 watts and have short (or limited) sensor cable lengths. With the Inkbird line of controllers (STC-1000, et.al.) I was able to put an appropriate size controller to handle a 1500 watt Coates inline heater in a waterproof housing, using custom length power, relay AND sensor cables. The accuracy of these units allow control down to 1 or 2 degrees of your set temperature, set it and go The Coates inline heater has a temperature knob to control the on/off and it's trial ail and error over many days to get it set were you want pond temperature. I leave the Coates heater in max and control it's on/off thru the controller which sits out of the way on a shelf and the sensor is in my RDF.