I just bought a Rheem Ruud EGSP20 electric water heater for the home I'm building for myself. I'm retired with no expectations of having any more kids. I bought the 20 gallon electric, because it was one of the few I could fit into my crawl space. There is just no room in the house itself to install a water heater. This water heater has no feet. I poured a 24"X24" concrete pad 4 inches thick for the water heater to sit on. I would like to put something on top the pad for insulation to keep the concrete pad from sucking heat out of the water heater. What can I use for insulation that will support the weight of heater and 20 gallons of water?