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How to make a candle heater from clay pots, and what it can really do
Nested clay pots over a candle make a small radiant warmer for a desk. They do not make a room heater, and they are never safe unattended.
- Filed
The clay pot candle heater circulated widely around 2010, sold ready-made by a small company as the “Kandle Heeter” for about $30 plus shipping. A homemade copy costs about half that in hardware store parts.
How it works
A candle flame gives off a fixed amount of heat. The pots cannot add to it; what they change is its form. Hot air rising from the flame collects in a steel core of bolt, nuts and washers and in the smallest clay pot around it. Those get very hot and radiate into the next pot out, which warms and passes heat to the largest pot. The outer pot, with its much bigger surface, ends up warm to the touch and gives off gentle radiant heat, the kind you feel on your hands, instead of a thin plume of hot air that rises straight to the ceiling. Clay also stores heat, so the unit keeps radiating for a while after the flame is out.
Parts
- 3 unglazed clay pots: 4 inch, 2 inch and 1 1/2 inch
- 1 bolt, 3 inches long by 1/4 inch
- 7 nuts, 1/4 inch
- 2 washers, 1 1/2 inch outside diameter with 1/4 inch hole
- 3 washers, 1 1/4 inch
- 3 washers, 1 inch
- 8 washers, 3/4 inch
- 3 metal corner braces, 4 inch, for the stand
Glazed pots are a poor choice; glaze can crack and some glazes are not meant to be heated.
Assembly
The bolt runs down through the drainage holes of all three pots, which nest inside one another with air gaps between them. Nuts and stacks of washers on the bolt set the spacing and hold each pot in place, with the larger washers clamping at the pot bases and the smaller ones stacked inside the innermost pot to form a compact steel mass that the flame heats directly. Tighten gently; clay cracks under a wrench.
For the stand, lay three 4 inch corner braces together with the middle one facing the opposite way, then bend the outer two just enough that the heater’s rim sits on them, well clear of the flame. One test build used a large homemade jar candle and added 6 inch braces to reach over it.
What it actually does
That reported test ran the heater for about six hours on a mild spring day. The outer pot gave off a small amount of warmth, more heat poured out from beneath it, and the builder’s honest conclusion was that it would not warm a house or even an ordinary room. One candle puts out something in the region of 80 watts, a small fraction of a portable electric heater. As a hand and desk warmer, or in a very small insulated space where someone is awake and watching it, it helps a little. The more useful lesson is the principle of turning a flame into radiant heat through thermal mass, which scales up in stoves built for the job.
Fire and air safety
This is an open flame under a hot mass, and it needs strict rules:
- Never leave it burning when you leave the room or go to sleep.
- Stand it on a stable, noncombustible surface, at least 12 inches from anything that can burn, out of reach of children and pets.
- Do not trap the candle under the pots with no airflow. An overheated candle can liquefy completely and flare, and a starved flame burns dirty.
- Do not use it in a car, as some early write-ups suggested, or in a tent where people sleep. Small enclosed spaces make any flame a fire and carbon monoxide risk.
- Keep working smoke and CO alarms where you use it.
The National Fire Protection Association’s candle safety guidance applies in full.