So you may be able to just add vents registers through the inside wall to get the combustion air you need.
Boiler room door vents.
The room is approximately 10 x 6.
The unfinnished area of your basement may give you the volume you need.
I want to close these doors.
Lets say you have a boiler room we call it a.
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The boiler is 125k btu input and the hot water heater in 45k btu input.
Now you need to find the required volume.
The boiler and wh located there and room b is the open basement space.
Both the doors have fire guards on them.
I keep the doors next to the boiler open at all times.
The room needs 50 cubic foot of free volume for every 1000 btu s input.
The air that s in the cupboard is sufficient for the boiler to do this so long as these clearance measurements are in place.
The room does get rather warm during boiler operation but i am most concerned about not having enough combustion air.
The space does have a basement window and the room is not air tight i also have also added a vent to the rest of the basement with a standard ac return vent.
There are 3 doors one for my tool room and 2 next to boiler in front of boiler one on the side.
Or you need to have combustion vents ducts.