Post a photo. It’s likely a combustion air supply.
Exhausting air is a poor method at humidity control. You’ll create a negative pressure in the basement with no make up air, and either start pulling air in from outside or conditioned air from upstairs.
“I haven’t failed. I’ve just found 10,000 ways that won’t work.” - Thomas Edison
“It’s not whether you get knocked down, it’s whether you get up.” - Vince Lombardi
"In this house we obey the laws of thermodynamics" - Homer Simpson
Local 486 Instructor & Service Technician