I use two large stock tanks with plug in heaters to water my 4 horses for the winter. We fill them with a garden hose (which is kept indoors when not in use) about once every 3-4 days or so. Through the winter months, the heaters are on pretty much 24-7. They don't have a temperature control, but do have a built in thermostat to keep the water just above freezing.
So my question. Is it worthwhile making an insulated box to cover the tanks? Cost of materials runs about $75 + for each tank if I frame out a box, insulate it well, vapour barrier the inside and cover with plywood. I cannot tell for certain how much the water heaters add to my power bill in the winter because we use so much more power for everything (furnace fans, lights, etc) else as well.
I know I can calculate the cost of operation, but I have no way of knowing how much less the heaters will run if the tanks are insulated. It gets really cold here (-20 a -40 C) in the deep of winter. Last year we had very little snow, so no snow insulation for the tanks. The year before we had 3 feet of snow.
Does anyone have any insight, experience or suggestions?