A gas water heater has a fire chamber below.
Setting it on foam would be useless.
It only makes sense with electric.
Terry, does it also make sense with sealed combustion gas?
NO! There is NO contact between the storage tank and the bottom of the heater.
HJ, I don't understand what you're saying. Would you explain a little more? Could the foam catch on fire being so close to the fire chamber on a sealed combustion heater?
"Foundations" are NOT poured over foam. Floor slabs are, or foam can be inserted around the floor perimeter. The foam under a slab is subjected to such ridiculously low loadings that the concrete will NEVER compress it.
But like I posted, standard 2lb density XPS can handle 25psi with 10% compression, which is 3600lbs per square foot,and you only need ~275psf. The footprint of a 20" diameter tanks is ~2.2 square feet, so nominally it'll carry the ~600lb load of a flat bottomed 50 gallon tank pretty handily in a static load condition. (600lbs over 2.2 square feet it a bit under 2psi, less than 8% of the load rating for XPS that yields 10% compression. I think you'd be good. 1.5lb EPS would probably be fine as well.
Terry, does the foam pad you get from your supplier have a product name? I am getting ready to swap out my electric tank and would like to get a pad to set the new tank on but I am having a hard time finding anything of this nature in Ohio.
OK Guys put a piece of plywood on top of the foam, problem solved<GRIN>
Thank you guys for your advice. You're a valuable resource. Here's what I did: put the water heater directly on the foam pad, which is in a drain pan on a plywood stand. The water heater went easily on the foam pad and didn't seem to compress it much. Of course it was empty. Filled it doesn't seem to either. Anybody see a problem with this?
It should be fine.
We just place the electric heaters on the foam pads.
I'm surprised that "plumbingpro" would add plywood over the foam. I've never seen that done in all my years plumbing.
You will need to Earthquake Strap though, you're on the West Coast.