My brother will be hospitalized for most of the winter. His old, uninsulated house is heated ONLY by space heaters. Low temps in the 20s at night, with occasional single digits. I have had the water turned off at the street and will run a small (safe, oil-filled) space heater, checking it every day or so. If I open the water spigots & empty the pipes, must I also turn off the electric water heater? I was hoping it might provide SOME extra warmth. Thanks.