Lacking combustion air

Lately I have run into several (many) open combustion furnaces the seem to lack enough combustion air. Originally installed in an unfinished basement, then the homeowner finishes it and encloses the mechanicals in a 10x10x10 utility room with wooden slats in the door (and no make up air pipes to the outside). I know you need 50cu ft of air for each 1k BTU. Some flames appear very yellow, which is a no brainer, but sometimes the flames are blue and appear fine. I always explain this to my client and recommend an HVAC tech examine and decide. Am I being a “chicken little” on this issue?

(general rule) If the opening is one sq inch per BTU it is fine,since it is drawing air from the entire basement.

Need opening top and bottom within 12 inch of floor and ceiling when not fully louvered or opened.

I of course am not considering other factors,such as if it is now a bedroom,small basement with little air,has a fireplace,no CO detector.etc.
If in doubt leave it to the HVAC Tech.

Bob - do you me 1 sqin per 1K BTU? And I know wooden louvres gets dowgraded to about 20% of opening size. The basements are now finsinhed with BR, Bath, FR, etc. The utility rooms are enclosed. Just curious

Yes ,sorry I was heading out for an Inspection.
I have a Pdf on it ,which of course does not fit here.

State of Kentucky dept of Housing has a download in microsoft xls on combustion air program. Punch in the numbers and it gives you metal and wooden grill sizes required.

Gary - Thanks - that form is awesome - solves many questions at once.