This is the best photo we’ve ever received revealing the carpenter’s engineering capabilities when it comes to sizing the opening in the plywood below an upflow furnace. Basically the carpenter has no idea of the needed opening when he built the floor of this furnace closet, so he simply whacked a hole between two studs. The installer failed to take the time to enlarge the hole when he set the furnace, and there it remained year after year, reducing airflow hour after hour.

Lesson learned: Teach installers to maximize the return opening when setting new or replacement equipment.