I saw this online, the Kandle Heater is, or was available from www.heatstick.com it is a very simple and easy design, you can see how it works. Should be easy enough to tell how much 1 lit jar candle increases the temperature in your house, just blow it out. Continue the experiment until you know for sure, I would think it would have to be a really big candle to make any difference.
All the best,
...

I saw this online, the Kandle Heater is, or was available from www.heatstick.com it is a very simple and easy design, you can see how it works. Should be easy enough to tell how much 1 lit jar candle increases the temperature in your house, just blow it out. Continue the experiment until you know for sure, I would think it would have to be a really big candle to make any difference.
All the best,
Dan.