Question isn't too clear. Water heater especially needs to have instantaneous access for when the bottom rusts out and pours water everywhere. The clearances aren't too large for safety but you must have a doorway for replacement issues down the line.

There is no suggested distance or limitations on the type of building materials? Actually, I am envisioning a series of sliding doors to divide basement area. Behind sliding doors would be furnace/water heater,sump pump, water softener & storage/closet area. I'm ultimately trying to carve out a sewing area in the other half of this section of the basement that is shared with laundry. I would love if the sliding doors (3-4) would function on separate tracks on the ceiling, so they would be able to expose the opening in multiple ways to allow for repair or moving larger items from storage.
My assumption is that these may have to be custom, due to the application & the fact that I would like the sides exposed to sewing/laundry area to have mirrors attached to them.