double-hung vs casement windows: energy difference?

building a house in mid-vermont, researching windows.i read that casement are more efficient than double-hung,but how much more?is it like 5% or 500%? building a house in mid-vermont, researching windows.i read that casement are more efficient than double-hung,but how much more?is it like 5% or 500%?Read MoreGreenBuildingAdvisor