Surely basic laws of energy generation mean that those candles will only generate as much heat as they can give out when being burnt. I'm not sure how adding the flower pots would make them generate any additional heat here? No scientist though could be wrong.
I would not think this a great idea in practice. Open flames like these candles being used all the time could lead to something catching on fire (I know people use candles all the time, but still...). Also they must give off something in the fumes here?
You're right, it doesn't generate additional heat, it merely improves the deliverence of the heat. Also I wouldn't worry about the fumes from 4 small candles, you probably breath worse when you open a window in any relatively built-up area.
