I'm partially finishing my basement, and I want to enclose furnace, pressure tank (well) and hot water heater by putting up walls.
Obviously, if something breaks, it'd be nice for a HVAC tech to be able to get at it / fix it without tearing down the walls, so I figured here would be a good place to ask how much space you need, around the furnace in particular (I don't think access to the hot water heater / pressure tank would be a problem).
The manual for the furnace basically says the clearances to the side/front of the furnace can be 0, except for the side with the access panels, and the top. However, I'm not sure how workable that is.
Here is a rough plan, there'd be about 28 inches between pressure tank and wall, which I think would be enough to replace the furnace if need be?
Also, here's pic (sorry, very blurry) of the furnace / return / plenum, to give you some rough idea.