Originally Posted by Ron6519
You're not measuring for replacement windows if, "I gutted everything to the brick opening in the wall." First off, you don't know what a replacement window is. That is a window that sits in the frame of the old window. Once you gut the window, you're looking at a ,"new construction " window.
You shouldn't pick up a tool until you know exactly what you're doing.
Try searching, "replacement windows" to get a handle on the subject and you see if your windows even qualify.
I've seen windows described as replacement windows if the do not have a nailing flange, and are instead intended to be secured to the framing solely through the window frame.
New construction windows use the flange that needs to be ancored to the sheeting behind the siding. The flangless ones can be installed without disturbing the siding. some new construction windows are designed to be converted to replacement windows. I'm thinking that would put more stress on the frame, so I wouldn't do it unless the manufacter specifically mentions it as an option.
to the OP's original question, you are looking for a window designed for a 36" wide RO, but it sounds like you might be able to go up to a 40" RO window (I think that would be a custom size) without messing with the structure, just the brick fascia. I'd stick to a standard size to save money and work in your shoes.