Making Storm Windows for a Porch

Also see if you can add insulation anywhere in the walls, as this will help keep out the cold too.

I'm not sure if this is what you are considering, but here are my ideas. You can get boards and cut to about 1 1/2" width and measure the length and width of the window to make an enclosed frame. Cover with clear plastic on the bolt you can buy at WalMart with different thickness choices and is inexpensive. These can be removed during good weather and stored and used several times over before having to put more plastic on the frames.

If you prefer the more expensive method, use plexiglass instead of plastic on the bolt. Measure your frame to fit snugly in the window. Saw in each board edge precisely the same to slide the plexiglass into the wood frame. Add the fourth board to the framework and mount inside the original window. Caulk any areas that may need sealing around the framework.