Thinking about cutting a door through my 8-inch concrete foundation wall, is this safe?

Cutting a three-foot opening in an 8-inch load-bearing wall is a massive job, and you defintely shouldn't wing the shoring. You need to build a temporary support wall about two feet back from the concrete. Use a double top plate and 4x4 posts or 2x6 studs spaced every 12 inches. Those floor joists need to be dead-level and fully supported before you even think about touching the saw, otherwise you’ll see cracks in your drywall upstairs within minutes of the first cut. Regarding the saw, a gas-powered or hydraulic **diamond blade** will cut trough rebar, but it’s going to be slow going once you hit the steel. You’ll feel the saw start to chatter or slow down; don't force it, just let the blade do the work. Make sure you rent a saw with a water hookup. If you try to dry-cut that much concrete, you’ll burn out the blade in ten minutes and fill your entire house with fine silica dust that won't go away for weeks. The trickiest part is the header. Most people cut the rough opening slightly larger than the door to leave room for a steel lintel. You'll want to cut your pocket for the lintel first, set the steel, and then finish the vertical cuts. Trying to slide a heavy steel beam into a hole while the house is hovering on temporary jacks is high-stakes. If you’re using a heavy header, make sure it has at least 4 to 6 inches of bearing surface on both sides of the opening. Doing this over a weekend is extremely ambitious for one person. Between the shoring, the actual cutting—wich is physically exhausting—and then hauling out several hundred pounds of concrete chunks, you're looking at a three-day project at minimum. And that’s before you even think about waterproofing or framing the new door. If you haven't operated a 14-inch concrete saw before, the learning curve is steep and the kickback is no joke.

That water hookup thing sounds like a recipe for a flooded basement. If I’m cutting inside, where does all that slurry acutally go? I’ve seen videos where it looks like a total swamp within minutes. Do you guys just use a shop vac the whole time, or is there some trick to keep it from ruining the rest of the floor?

Also, how heavy are those concrete chunks realy? If I cut out a 3x7 foot piece, I’m guessing it’s way too heavy to lift by myself. Do you usally have to cut the opening into smaller, manageable bricks first so you don't break your back hauling them out?

You definately shouldn't try to drop that 3x7 slab in one piece. A chunk that size weighs over 2,000 pounds. Unless you've got a crew and some serious rigging, it’s a death trap. I always grid my cuts into manageable "bricks," roughly 12 inches square. Even then, an 8-inch thick block that size is still nearly 100 pounds. For the slurry, I build a temporary dam with spray foam and have someone manning a high-powered shop vac right at the blade. It’s still a mess, but it keeps the floor from becoming a lake. Wear rubber boots too; that slurry is caustic and will ruin your skin if you're standing in it all day.