How to Build a Cabinet Over a Furnace

Arrange two plywood boards which are 1/2-inch by 3 inches more than furnace height by 3 inches more than furnace width on the working surface, parallel to each other. Set their long, thin sides on the working surface with the help of an assistant. Lower another of these boards on top of the first two and arrange them so that their edges line up evenly. Drill holes every 12 inches through the top board and into the other two side boards. Set 2-inch wood screws in each hole and securely fasten them together.

Place the three boards around the furnace, with the uncovered section on the side that has controls to which you will require access. Hold another plywood board of the same dimensions as the first three, which will be the front board, up to the furnace and mark the area to which you require access.

Remove the front board and cut an access panel out it, cutting the entire board into three separate pieces if necessary, or simply make a small door cut out of the larger plywood board. Hold the plywood that is not part of the door up to the three assembled pieces and line up the edges so that they are even. Drill holes every 12 inches into the new board and through to the installed boards. Attach them in place with 2-inch wood screws.

Put the door board back into place and slide two hinges between it and the plywood cabinet. Mark the locations of the hinge screw holes and drill pilot holes in each marking. Screw the hinges to the door and the plywood cabinet using 1/2-inch wood screws.

Measure the dimensions of the width and depth of the top of the cabinet boards and cut two 1/2-inch plywood boards to fit. Hold the boards against the top and bottom of the furnace and mark any areas that need to be removed to make access for pipes and other fittings. Cut out these areas with a saw and position the boards in place. Drill holes every 12 inches down through these boards and into the cabinet boards. Attach the boards in place with 2-inch wood screws in each hole.