sliding patio door on slab on grade
 

I live in Michigan in a house on slab on grade which can be cold in winter. I have one standard size window that I am thinking to taking out and putting a patio sliding door. The house is brick which means I have to cut the brick. What I am afraid of is the winter cold. Will the room be realy cold in winter since now it will have double the glazing? even tough the existing window I have is Aluminum.Any advice is appreciated very much. Jake.

Somewhere there is an engineer who can calculate sq ftg and thermal exchange, but all i can say is I replaced an old aluminum patio door with an Anderson wood door (same size) and it made a world of difference.
I have a walk-out basement and the installer put a treated 2x4 in for a sill. I always felt this is a weak spot in the installation but it has stayed dry.