I have my 420 on the main floor (above a basement). I was doing work on my house at the time, so my contractor opened the ceiling below the tank, tripled up the floor joist in the middle of the tank (the joists are parallel to the tank) and then put a steel column under the joists). It'll hold up the whole house. I agree with Liontamer to check with a good contractor. But if there's a will, there is usually a way.
LOL