In many peoples minds the idea of a sunroom or room addition on their house meshes with how they can use the room.  Will it be used only in mild weather, or will it be most valuable to them if it will be used in all seasons and all temperatures?  At some point the idea of a sunroom may cross over into a full room addition with multiple functionality.    If  a homeowner wants all season/all-weather use of the new room addition, then energy efficiency in design and in construction come into the equation very quickly.   Wall thickness, insulation type, window type  & design, roof overhangs, floor insulation, and remote heating and cooling all interact to impact comfort levels and energy usage.  Even if the consumer is not focused on energy efficiency, wide temperature swings impact comfort levels and can make a room less comfortable.   In many cases it is difficult and expensive to extend the houses existing hvac ducts to the new room.  Even in the case where there is ready access to the existing heating system there is a potential issue if the existing system is adequate to heat and cool the new room.   In many cases a remote mounted dedicated hvac unit is the best alternative.   Fortunately great improvements have been made in the design of these units in the last decade.  Everyone is familiar with the wall mounted  air conditioner that is so loud it interrupts your sleep in a hotel or motel.  Today similar units combine heating and cooling, are very quiet, and use  digital thermostats to allow dedicated temperature control of a room addition or sunroom.   This dedicated unit can offer many advantages, not the least of which  is the ability to regulate the room temperature independent of the existing home.   In addition when the room is not in use it is possible to conserve energy by setting the thermostat to the best temperature for energy efficiency.   In many cases the installation cost of such a dedicated unit will be less than extending the existing duct work, and it will work better.  If energy efficiency is taken in to account in designing the room,  it is possible for the new room to be more energy efficient and comfortable than the rest of the house.