Bricks, Masonry, Asphalt and Concrete - Ok to punch hole in cement block wall?

Years ago an addition was put on to a house I recently purchased. I'm having new forced hot-air heating installed and access through the basement is limited.

The installer needs a 12" x 12" hole cut through a cement-block wall.

Do I need to be concerned about structural integrity? The rest of the wall is uncut. There is only one floor above (and I'd like it to stay above!)

Any advice is appreciated.

What size is the wall, (Height & Length)
Is it core-filled and have rebar in it?
What size blocks?

I think these specifics will help answers the question. If the wall is 24" high, 12" takes 1/2 of the structural integrity...

I don't know if this answer is correct or not but when I lived in fla I worked on a lot of block homes. There were a bunch of them that had jaccuzi tubs and code required that the motor/pump have 16" x 20" access. This was often done by cutting a hole out of the concrete block. [for access from outside] I never saw any lintel other than the 2x8 the opening was framed with.

another question is what is the location of the hole in relation to the wall? bottom by slab? mid section or upper portion just below sill? all i know is in my michigan home, the bathroom was an addition after the original house was built ( orig. gas lights, coal furnace, and outhouse to boot) when they ran the main waste drain they cut approx 12" to 16" square and they cut it from the sill plate down and i can now see the sill above the open access hole is sagging so careful where u cut/