Funny to check in here and see this thread this morning. I just "made" one of these yesterday for chix and giggles after seeing a video posted yesterday from one of my Tiny House sites. A DIY Tiny House Heater - YouTube
His method made more sense to me than using all the nuts and bolts..I have seen these before and went "Thats a lot of work for so little gain"..so I never made one. The concept of adding more stuff (Nuts and bolts as a heat sink) inside the pots has never set well with me..seems inefficient to have one thing absorb energy to radiant it to another thing and get a lot of loss along the way.. I know it doesn't work for electricity flow..I am not a scientist, but I suspect it is the same for all energy sources.
The one I made simply has a metal knob drawer pull dropped into the hole of the inner smaller pot. The inner pot then heats up to unbearable temps, heating the air between the two pots. The air caught between the inner pot and outer pot "Shoots" out the top hole, sort of a mini passive forced air furnace
. With the nuts and bolts, it is purely a radiating heater.
I used a 4" inner pot and a 6" outer pot, both from Home Depot..cost about $2.50 total. That's cheap enough for me to try :-)
I tried this after the sun went down so that I would not get passive solar
heat in the mix. I used only 1 candle. As a heater..well, it sux..I started in a 60 degree trailer. After 2 hours, it was a whole whopping 70 degrees. I made these measurements from my normal sitting spot, about 5 feet away from where I was running the heater. I suspect some of that temp increase was from..the exhaust from my laptop..2 beagles and a cats body heat, and the cuppa coffee I had sitting out and was happily sipping on while I contemplated putting on a hat and another pair of sox.
There WAS an UNINTENDED positive aspect to doing this that made perfect sense to me, after I saw it happen. The cheap consumer thermometer I am using has a humidity gauge on it. I saw that in the beginning of the experiment, the relative humidity was 70%. By the end, it was 42%. And it was dry (re: In Oregon, that means it isn't raining...yet) outside when I started, pouring down rain by the finish. Perhaps this may be a better use for this system..a passive dehumidifier? Just like Arizonians say "It's a dry heat"
As a side note, after 30 mins, the air exiting the top hole measured over 120 degrees at a distance of 1 1/2 ft. That's as high as my cheapo thermometer goes. Move the thermometer another 2 feet away, the temp drops to 80. And another 3 feet away, where I was sitting..60. It didn't get to 70 until the thing was burning for 2 hours.