Laura watched a video about a convection heater powered by tea lights and suggested I try it in my office on chilly days.

I tried it out a couple of times and it does make my little office reasonably warm. First the inner pot with the hole blocked up. It sits on a bread tin, which contains the lit candles:

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Then on goes the outer pot; note the second bread tin to keep the first off the book underneath. The first bread tin gets very hot:

P1020872The Internet has picked over this a lot, trying to decide if it’s better than having just four candles burning without the fire-hazard construction on top of them. I’ll add my thoughts: the amount of heat generated is not changed, rather the way the heat is distributed is. So four candles send the heat straight up, with a weak convection current caused by the hot air rising. The pot heater increases that convection current to help circulate the heat a lot better and also stores the heat before releasing it as radiation, which travels in straight lines outwards. Both these contribute to making me warmer than the four candles would.

In other words, it’s a simplified masonry heater:

The same source has a diagram of the pot heater:

If I had the inclination, I could come up with some more mass to store more of the heat and so on. Maybe once I’ve done my rocket stove I’ll get to that.

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