Here in the Treasure Valley of Idaho many home owners complain of rooms in their house that are too hot, too cold, too often. Think about it. If you have a a two story home I can almost guarantee that you complain about that bonus/family room upstairs being too hot in the summer. Many have bedrooms upstairs, or master bedroom at the far side of the house and always seems cold in the winter. Or maybe you have put on a room addition, sun room, or decided to have a shop or craft room put in the garage and now you need it to be comfortable. What is the solution? @comfortguyjerry would highly recommend a ductless heat pump. They are a perfect solution. What is ductless? It is just that. No built in duct work like your present furnace and A/C use. Instead you have an outdoor compressor about the size of a large suitcase. From there they run all the copper lines, electrical, etc up the wall in a covered channel and drill a three inch hole in your wall for the lines to through to the indoor wall unit, which is the evaporative coil/fan. The wall unit usually is mounted up close to the ceiling. The fan runs at whisper quiet, and special technology uses electronic sensors to locate hot and cold areas of the room and adjust the variable speed compressor to make sure of even comfort. No blast of cold air like from a widow air condition and not hot radiant heat that you can't get to close to or you will roast.
The benefits are numerous! No duct work, real comfort. Highly, highly efficient, and super quiet. Clean air to breath through a series of air filtration systems that give you clean air continuously. They provide both heat and cooling in one unit. There are several brands out there but @comfortguyjerry recommends Mitsubishi Ductless Heat Pumps for quality and durability.
Ductless units are being used in over 80% of homes in Japan, China and Europe already, and have been used for decades. For more information check these websites: www.mehvac.com or www.greensheating.com.