Build a cold-air return frame from leftover hardwood flooring

Step 1

Begin by picking through your leftover hardwood and select pieces with consistent grain. Install a dado blade on your tablesaw and use it to cut a rabbet along the groove side (as opposed to the tongue side) on the back face of your hardwood flooring. The goal is for the rabbet to cover the metal edge of the cold-air return cover, leaving just the grill visible. If you start with 2 1/4"-wide hardwood, as I did, this should give you frame pieces that measure 2" wide, almost the same width as your new floor pieces and a nice visual complement.

Step 2

Next, flip over the pieces and remove the tongue using a ripping blade in your tablesaw.

The bottom strip is treated differently than the other three pieces. Rip it down to 11/4" wide. Leaving it as wide as the rest of the frame would result in the grill being raised considerably higher up the wall than the original grill position. In that case, you would likely need to adjust the location of the opening in the wall, which involves more work and mess. The rabbet here is made a bit smaller as well, since the bottom edge is only 11/4" wide. Give it a few inches of extra length so you have enough material to make a hidden lap joint.

Step 3

The top and side pieces are joined with 45º mitred corners. The bottom strip, since it is so much narrower, fits between the side strips with what appears from the front to be a simple butt joint. In actual fact, you need to make a lap joint to fit the bottom into the rabbets of the side pieces. Adjust your dado blade to roughly 1/4" above the table, then use the mitre gauge to run the bottom strip across the blade to cut a lap joint at the two ends. Glue and brad nails make short work of the joinery, and your frame is almost ready to be installed.

Since the face of the wood is already finished to match your floors, you just need to apply additional finish to the outside and inside edges. In my case, I started with unstained natural red oak. Clear polyurethane matches very closely with the neighbouring factory finish.

Installation is now a simple matter of fitting the old metal cold-air return cover inside the new wooden cover and screwing the assembly into place on the wall.