Alright guys bare with me. I am installing a tankless water heater in my basement. 1924 farmhouse with stone foundation. In the venting kit, it came with 2 wall thimbles, one for the inside of the wall and one for the outside of the wall. When you put the two thimbles together there is 6 inches of space between the two. This space allows for the wall thickness. Here is my problem, not only do I have to drill a hole in the outer wall, I will also have to drill through one floor joist. So the thimble will not be thick enough. What do I do? Buy another set of thimbles and put them on each side of the floor joist and run the vent pipe through the joist and then the outer wall? The floor joist is in the way and I can't avoid drilling through it.
I presume that this joist is a few inches from your rim joist, or in close proximity to the rim joist? Drilling the joist will cause it to be overdrilled and will make it structurally useless. Can you possibly cut out about 18" of the joist and header it off to the adjacent joist and the rim joist? Not hard to do at all...That way you're just penetrating the thickness of one rim.