Like I really need another hole in my head...

[Bruce Seidner]

Prudence would dictate that I ask about the consequences of knocking an eight inch hole in the foundation gray cinder block of my home. I noticed that the HVAC installers gave little thought or pause to knocking a 4" vent when they installed a gas heater years ago, but this is an 8" hole.

It would be great to have a straight run from the outlet of the blower to the wall, but it is not too out of the way to get to a vent block that has 3holes in it already. the two middle support walls would have to go and the hole enlarged but that was one thought.

Is there some sort of support lintel that is necessary or do I just draw a circle, take out the hammer drill, and break on through to the other side?

I suppose, it being hollow cinder block I could get a wheel barrel of quick cement and fortify the surrounding voids but am unsure if this is necessary.

Basically, I have no idea, and while I might resist asking directions when I am lost, I am not feeling any such loss of standing by asking about this one.

[Larry Edgerton]

Unless it is an area with a concentrated load such as just below the vertical supports for a large header I would not be concerned. In remodels I routinely take out sections of foundations much bigger than that with no ill effects so long as they are not in a critical area.

Larry

[Aaron Berk]

A picture of the wall in question would be very useful here, especially if there are open joist cavities to see.
Not knowing whats above makes any ones answer nothing more than a guess.

[Anthony Whitesell]

I'm only taking of this from visual experience (ie., I saw it done). A relative was doing a remodel and needed a large hole in a cinder block wall. They ended up knocking out the row above plus one block on either side and added a half-height block back into the extra hole and a pair reinforcing I-beams. I guess they would have been around 3" tall and wide. On the outside they cut the cinder blocks to fit within the out channel of the beam. I presume this was (a) to maintain the look, (b) so the steel wasn't directly exposed to the outside world. I'd say the hole was 12-18" square and I don't recall what was above or around it.

Just proposing an option to look into.

[Bruce Seidner]

This is all very helpful. The wall in question is about 5 blocks tall before it is the foundation for the full house brick wall above. The brick wall runs the whole length of the foundation block. I can't see that there is any difference or critical points along the length of the wall. But it does seem that there would be a way to reinforce the cavity. with solid block pieces and cement.