Large Vertical Hole Foundation

Filling it with masonry seems to be the best as far as compatible materials, but before you do, think about the future. Will you ever have need to run wires, vents, or anything else to the outside? If so, you may want to take a more temporary approach.

On the outside, I'd use brick and mortar to match the existing brick as close as possible. . Once sealed, you can even fill the rest of the void with expanding foam spray. That would make it easier if you ever wanted to add a vent for a high efficiency heater or power to an outbuilding. If you want solid, build it up with some stone and cement mix, probably in a couple of steps, unless there is a way of attaching a board to act as a form and hold everything in place.

It's too big to camoflage with a dry vent cover, so see if your hardware store has a cap you use when removing a chimney, a chimney cap, an exhaust fan cover or something like that. Then insulate behind it. That would be the cheap and easy way to do it -- not the best way, just the easiest.

snipped-for-privacy@aramark.com wrote:

Mix a bunch of cement in a bucket, and stuff it into the hole?