I read this article a couple of months ago and made the setup to try it out. I used 4 tea candles and 2 pots just like he did,with the tea candles inside of a meat loaf pan that I lined with foil so it wouldn’t get ruined. I placed it in my bathroom which is about 8x8 with an 8 foot ceiling and put a thermometer a couple of feet away. After about an hour the pot was nice and warm but the room temperature hadn’t budged. The tea candles also didn’t last 4 hours but they did last over 2, close to 3.
Bottom line is that it will work. It won’t warm a room but it does make a nice hand warmer. Since I had the thing set up I actually did use it as a hand warmer while I was watching a movie one evening and it was okay for the money. If you have all of the items already available like I did it’s worth a try. I wouldn’t go out of my way to buy and make one though.
I bought some zippo hand warmers (new) on ebay a few years ago. One for each of us - throw it in a sleeping bag and should keep us comfortable.