It can sit behind the stove, either on the floor or mounted to a board. Consider two things though:
1) We would recommend that the top panel (with the printing on it) either be facing up or have the unit mounted on a board so the unit is vertical. This is because the top plate of the module is a heat sink and should be exposed to the open air for proper cooling.
2) If installed in a basement you may want mount it on a board to get it up off the floor, where condensation or even flooding may come into play.