I recently bought a new home. It does not warm as well as I think it should and is costing quite a bit more for gas than my last home which was larger. Can you tell me the approximate size a furnace I need? The house is 1700 square feet. It is rectancular with the larger two sides facing the south and the west. ALL the ceilings are 9 feet. Three rooms have windows that a quite large and basically cover a whole wall. The other rooms have regular size windows. Thank you for your help!