Return air chamber under the furnace
My furnace is in my garage. It sits on one end of a long 24"HX30"D X7'w platform which has at the end a 16"X32" with cold air return grill opening into the house.
This long chamber/platform is drywalled on sides but has wooden planks on top except where the furnace is mounted. There is no duct connecting the vent and the furnace.
The house was built in 1972. Is this allowed? So far no issues but should I be concerned that air from garage may enter the house through this?
Would appreciate your advice. Thanks.