There is a gap at the bottom, like a toe kick. Then behind that we box in all 3 sides (so nothing rolls underneath there). Then the furnace is raise up higher than the height of the gap. An even better way is if you use a carpeted board on the back side and run it a little higher yet....but we wanted to make it possible to work on the furnace if need be.
Of course we covered that big front hole with a solid removable panel.
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