I am about to install a 50-gallon Rheem heat pump water heater in our garage at our house near Pasadena, CA. (after this installation, our home will be all-electric. yay!)
I watched Bruce Manclark's and Wade Cohn's excellent how-to installation video and noticed the EPS insulation pad. They seem like a good idea. It sounds like they're required by code in WA (and presumably readily available there), but are not easily acquired online or in-person in our area. So here's the question: would it be okay to use 1" polyiso rigid foam (which we have a LOT of scraps of) as an insulation base instead of the EPS? Is there anything special about this EPS?
The garage is concrete slab on grade. It looks like the highest compressive strength version of EPS is about 25 pounds per square inch (PSI)? According to the manufacturer of my polyiso, its rated compressive strength is 20 psi.
The area of the base of the water heater is about 388 square inches. The empty weight of the water heater is 178 lbs. Fifty gallons of water weighs about 417 lbs. So the full water heater should be something like 595 lbs? Divided by the area of the base (assuming the load is distributed uniformly) gives a load of about 1.5 psi? And polyiso's rated for 20 psi, so -- we're good to go?
Does this sound reasonable? Anything I'm not considering? This will be my first water heater installation. Thanks for your help.