Here’s How they work...Heat is applied to the oil through the heater tube and warms the oil closest to the heater.As the oil absorbs heat it begins to rise in the tank.As the warm oil rises, colder oil moves in to take it's place and the cycle continues.long as heat is applied to the oil it will continue to rise and fall in the tank.is not a significant rise in overall temperature within the tank, it is the oil movement that helps prevent the oil from gelling.

Model TH Heater
Model TH tank heaters are designed to prevent fuel oils from gelling in outdoor storage tanks. These heaters are inserted through any available tank top opening that can accommodate or be reduced to 1/2 NPT thread. This model is used primarily in tanks that draw oil from the bottom or side of the tank rather than from the tank top. The heater is installed as close as possible to the oil outlet.

Model DTH Heater
Model DTH tank heaters are also designed to prevent fuel oils from gelling in outdoor storage tanks.Unlike TH heaters, these heaters consist of an outer draw tube, the tube that extends down into the tank to draw oil out by pumping from the top. This model heats the oil in the draw tube so the first oil out is the warmest. When the oil isn't being pumped it acts as a standard tank heater.