It also depends on how high off the ground you are. Be aware that (at least in Wisconsin) if you are more than 24" above ground to the floor of the room, you can't use a vinyl product like PGT Eze-Bre ... read more
You might want to have a energy assessment done through a program such as Home Performance with ENERGY STAR or a utility-specific program in your area. WIndows often cost a LOT (for a quality product) ... read more