I’ve been trying to find a chart somewhere on the free area of register covers but have been unsuccessful.
I did an inspection at a condo where the furnace was draft induced 88,000 BTU/Hr input sharing a utility closet with a 52,500 BTU/Hr input water heater. Both appliances were behind a fire door with no air input on the door. I saw 6 x 9 vent in the ceiling in the closet.
The furnace mfg recommends 1 sq in of free area of outside air for every 3,000 BTU of combined appliances. In this case it would be 46.8 sq inches.
52,500 + 88,000 = 140,500
140,500/3,000 = 46.8 Sq In
If there wasn’t a register cover, the area would be 54 sq inches. This is really close and being technical but it’s one of those DLR’s. (Doesn’t Look Right) And I don’t want to Refer a HVAC Tech if it’s OK.