More Combustion Air Needed?

I inspected a house yesterday where the furnace was in a utility closet shared with the water heater and Washer/Dryer. The total closet is about 40 sq ft, but it has two access points. The closet sits between the dining room and the kitchen. On the kitchen side there are double bifold doors (solid hollow core, not louvered) for acces to the washer/dryer. On the dining room side there is a single bifold (same type as kitchen) for access to the furnace. All of this is on a concrete slab foundation. The furnace has a couple of inches clearance to the wall on the left and behind and is open to the rest of the closet on the right. This all had me concerned when I found two vents in the wall behind the furnace. Since there is only a couple of inches between the wall and furnace, I couldn’t really get in there to measure the vents, but there were two of them. They were filthy dirty with dust (see photo - arrow pointing to vent). Since this closet sits in a room with a trussed, cathedral ceiling, I couldn’t get up in that part of the attic to determine where the combustion air might be coming from. Saw nothing on the roof that appeared to be a source. The soffits were vented so there may be a duct running over to them, but again I could not confirm.
Anybody ever see anything like this? Any comments? I told the seller to make sure he cleaned the vents and to ask an HVAC specialist to come out to evaluate and verify that there was enough combustion air.

Really SIMPLE and Rough formula for determining if C/A is needed OR not.

Total Btuh / 1000 x 50 cu.ft = Confined OR Unconfined area.

Example: 100,000 btu furnace and 40,000 btu water heater = 140,000 btu in room

Therefore: 140,000 / 1000 = 140 x 50 cf = 7,000 cf

If the room is at least 7,000 cubic feet in size its UNCONFINED and has adequate Combustion Air (C/A)

If the room IS NOT 7,000 cubic feet OR bigger its CONFINED and needs Combustion Air

NOW … For your room if its about 40 sf (8’ x 5’ approx) AND 175 feet tall its OK and does NOT need Combustion Air. IF however the room is less than 175 feet tall - ADD Combustion Air.

I’m not a fortune teller BUT I’m betting the room was UNDER 175’ tall

If you NEED to ADD combustion air, you typically have 1 high and 1 low.
About 12" from the ceiling and about 12" from the floor, and at least 100 to 144 square iinches in size. DID you have it??

Personally I wouldn’t give this a 2nd thought / It would be an automatic:

“In my opinion as a professional and competent home inspector, the amount of combustion air OR combustion air sources that are provided are inadequate. This has the potential to be a significant safety concern. I recommend having a professional HVAC contractor install the proper amount and type of combustion air sources at the correct location(s)”.

You seem to have more factors to deal with, here, than simply providing sufficient combustion air.

Here in your closet, and the room(s) it is located within, you have a competition for air between the residents (# of bedrooms times 2, plus 1) that will require 15 cfm for each, combustion air (as noted), presumably a kitchen exhaust fan drawing air to the outside, the clothes dryer drawing air to the outside, the possibility of an unmentioned return air vent in the kitchen or dining room, and the necessary amount of air to draw the bad air through the various exhausts.

Not only do you need to provide sufficient combustion air, but you are also wanting to ensure a positive pressure within the space so as not to draw the intended exhaust into the room and/or create spillage at the burner (s).

This may involve more than a simple mathematical calculation.

Just something to think about.