Re: cold 20' x 16' familyroom - built on slab
I would echo Canuk's comments. We have a similar family room that is not original to our house, and it is the coldest room in our home.
Have you thought of checking your wall insulation to see if that may be part of the problem? I am convinced that part of our problem is that the former owners cheaped out and/or otherwise half-assed every renovation they did, one of these things being a lack of sufficient insulation in our family room walls.
-Daryl, learning how to keep up with an 80 year old house in PA