Clearances for an uncertified stove are 36". These can be reduced by as much as 67% to 12" with proper wall shielding. 12" is the minimum clearance unless the stove manufacturer has tested and documented lower clearances with a wall shield in the manual. NFPA
211 allows the maximum clearance reduction if the shields are installed permanently and there is a 1" ventilated space behind the non-combustible shield. The shield material can be metal or other non-combustible like cement board. Drywall is not acceptable. If the cement board is to be tiled use latex-modified Thinset
. The shield should have at least a 1" gap at the bottom and top so that air can freely convect behind the wall shield. It is attached to the studs in the wall with 1", non-combustible spacers. Ceramic spacer can be bought online or you can make them out of 3/8" copper pipe, or if working with cement board, you can snap off 3" wide x 36" strips of cement board, double them up and screw them to the studs to make vertical 1" furring strips to create the 1" air gap.
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Here are additional good tips for making it WETT certified if you are in Canada