I have an sunroom that is uninsulated and gets really cold in the winter.  This heater works well in cutting the cold down significantly and keeps the furnace from having to work as hard.  It does a better job than my ceramic heater and I think is more energy efficient as the oil retains the heat longer.  Just don't expect the unit to provide instant warmth.  It takes a little while to initially heat the oil.  I can feel a different about 20mins after turning it on.