Doors and Windows - Installing New Steel Door

I want to change my backyard and side doors to my home...my husband and I along with my brother will attempt to install the new steel doors ourselves...we decided that we would use the existing frame because we just did siding on the house ...but the new door comes with a frame on it...my husband said it shouldn't be a problem removing the frame from the new door and installing it ..... and working with the existing frame...I am not feeling this....any suggestions.

Metal (steel) doors come prehung. Install them that way.

You'll spend a couple hours installing a prehung door, or a full day (or more) trying to make the door fit your existing jamb.

Lefty is right, and you will also void any warranty you have on the door if you try to retro fit

I know this is an old post, but anyway, many steel door manufacturers make a replacement door to fit inside a existing door frame. It comes pre hung in a metal frame. You have to remove the old door slab, hinges, hardware, and interior trim. Then you install it from the inside into the old door frame, nailing through slots in the metal frame into the studs. Similar to a nailing flange, but on the inside. Then the casings go back on the inside, and there send a new seal for the outside which you butt up to the door when it's shut, and nail into the frame. I personally am not a fan of this type of install. I would much rather have a new wood frame, but if somebody is bent on not removing the old frame, this option is available.

Replacing a slab almost alway involves some trimming of the new door. They rearely just pop into the existing opening. Steel slabs come with very minimal wood edging to be sanded or planed. Installing a prehung is usually actually easier than replaceing the slab. It can be done without disrupting your new siding. The inside casing is easily dealt with.