How high to raise water heater above floor?
Regardless of code, I like to get them off the floor just in case the basement floods. My preferred (and easily available anywhere) solution is a few solid concrete blocks; one under each foot. You can stack them if you want, too. This is an easy way to increase the height in 4" increments. 

I don't suggest using lumber. If your floor is the least bit hygroscopic, it will rot from the underneath even if the tank never leaks.

16" x 8" x 4" Solid Concrete Block:



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