Most automatic waterers these days, that require a water line to be run below the frost line, will require a riser tube of some sort. By this, I mean a tube to center the vertical portion of the water line in. So what is the reason for this and what can be used for this riser tube?
The overall intention for a riser tube is to prevent frost from carrying over to the waterline, thus resulting in slushy water or a frozen line. The supply line touching the riser tube is the most common cause of the supply line freezing. A common misconception is that if the riser tube is filled with insulation, wood or other foreign material, this will prevent the freezing. Since frost can migrate, any fill in the riser tube will only increase the chances of the lines freezing.
So what should be used for a riser tube? Many things have been used, larger PVC pipes, concrete tubes, just to name a few. However neither of these materials will provide the ultimate protection to the automatic waterer during the winter.
Iowa State University in Ames, Iowa conducted a study during the winter of 1992-1993. Their studies indicated an insulated water supply line helped maintain temperatures above freezing. The same study showed insulated water supply lines with an 8″ inner diameter and an 12″ outer diameter provided optimum freeze protection and sufficient access for service. They found that this size would help retain the heat of the water as it went through the water line. This helped to prevent freeze-ups even when ambient temperatures were far below the freezing point. A second portion of this study also showed that there is no ground heat going up the thermal tube to the automatic waterer and ground heat cannot provide enough heat to keep the waterer from freezing.