I have built a closet around a furnace that is in the corner of the dining room. All that is left is the door.
But the door needs to accomodate combustion air (the return air is through a duct in the side of the closet).
I don't like fully louvered doors because they are a pain to maintain (clean and paint). Also, the customer is anxious for any marginal gain in quitness that might be achieved (I guaranteed that they would still hear the furnace easily).
So I want to cut a hole in a flat slab and put a vent into it. But how big a vent does the furnace need?
I couldn't find a BTU rating on the furnace. I did find a label with several numbers on it including:
Next to that is "Output" but without a number underneath.
The exhaust pipe is 4" diameter (but it gets bigger a few feet up).
Another day, another tool.