Fireplaces, Heating Stoves, Flues and Chimneys - Roughed-in fireplace

I wasn't sure if I should put this post in the basements/foundations forum or this one but I live in a mid-seventies, 2-story home in Ontario and my wood-burning fireplace is in the family room on the main floor. I hope I can explain this clearly but even though the firebox is on the main floor, the fireplace is "roughed-in" below the firebox into the foundation wall all the way to the basement floor. The empty space in the foundation wall is partially closed in with concrete block (the foundation is poured concrete) as if it was some kind of building code that this area couldn't be open or used. It would make a great storage area so I am wondering if anyone knows what the deal is with taking out the blocks and using this space.