For those upgrading from NG->HPWH, suspect most will gain space as we did.
We replaced our 50G NG water heater a few years ago with a 65G HPWH. The larger storage capacity HPWH takes up less space as we were able to remove the elevated platform that is code for NG but not HPWHs:
- Water heaters installed in residential garages shall be elevated on platforms so that the flame
or burner is a minimum of 18 inches above the floor unless listed as a flammable vapor
ignition resistant burner. (CPC 507.13)
Additionally, no flue on the HPWH, so now we have several feet of space above the water heater we can use for something else in the future.