Active Flower Pot Heater



About: Former electronics technician, former MIS tech support, former corporate call center help desk tech support

This heater was built before the other one. It is an ACTIVE HEATER because it uses a thermometer controlled fan.

This instructable describes the building of an active flower pot heater. What does ACTIVE mean? Active means that it has a fan for moving the air from the heater and the fan is controlled by a thermometer module. When the temperature reaches a certain point in the central core the thermometer turns on the fan. It does not use tea candles to heat up but can. It uses gel fuel like that used in camping or to keep food hot in catering operations,buffets and such. This pot heater was built as a solution to a problem, specifically that my garage is in the back of my yard, is not insulated and it is cold in the winter here in Toronto, and I can't spray paint in temperatures in the -C's. This active heater plus a passive pot heater will provide the heat necessary to warm up a paint booth 36"x36"x21". This 8 inch heater reached temperatures above 150 degrees Celsius at the top of the middle pot.

Getting the Facts Straight

For thousands of years humans have been heating rocks to serve as heat sources during the night. Advanced pre-industrial societies using similar technologies to heat their homes. Fireplaces being one.It is still being used today in poor areas. I don't know who or when somebody came up with the idea of using flower pots as heaters. During my research into this I came across many ideas and permutations on the flower pot heater idea. They all had the same basic parts plus a few other additions, but they all had short comings, that they all treated this as "Oh look at me I made this heater out of flower pots a steel rod some nuts and washers and tea candles". In all of them none of the flame from the candles was touching the rod. Then came the NAY SAYERS, THE TRUMP DISCIPLES trying to debunk the idea with science and to my observation failed miserably, the CHICKEN LITTLES on YouTube commenting that you should not do this because of the toxins in the clay. First of all flower pots are fired in order to seal them so that the moisture stays in for the plant to use. And then there are those I call VIRGINS, they haven't built anything but have the need to comment.

YOU HAVE TO PUT FIRE TO THE METAL otherwise this thing produces little heat and is useless.

Materials Used
1 x W1209 Temperature relay controller

3 x flower pots of different sizes

1 x piece threaded rod -mine six inches

1 x thick aluminum plate

2 x metal tins

some nuts

some washers

a piece of metal

some steel wool

some aluminum strips

some bike wheel spokes

some 14 gauge copper wire

some 1/2 inch copper pipe

a piece of plywood

a couple of 8 1/2 inch wide cans

fiberglass insulation

Tools Used


drill bits as needed


metal shears

screw drivers as needed

Step 1: SAFETY

The shinny stuff on the rod, the nuts and washers is galvanizing, to prevent rusting. It is BAD for you when heated. Before building one of these you MUST burn the shinny stuff off, use stainless steel or welding iron.Burn by creating a fire put the pieces in the fire and step away from the fire. Do this outside in ventilated space.See pictures. After the burn clean the metal with wire brush, wear a NOSH N95 mask.

Step 2: The Build

Part 1 - Assembling the Pots

The build of the heater differentiates from others in that I used a large metal plate at the bottom where the flame touches the metal, The heat transfer unit is made up of two sets of fins separated by pieces of copper pipe a nut and washer. the small pot then goes over this assembly, a washer and nut added to top of small to finger tighten the assembly. Following is a nut and washer spaced to accommodate the middle pot, followed by the middle pot, a piece of aluminum , a nut and washer, followed by the outer pot. The outer pot is finger tightened to the assembly with a washer and nut. Holes were drilled on the top of the outer pot for exhaust, to attach a can to act as a collar to attach the exhaust pipe, and a hole for the temperature probe. The collar was attached with two screws, followed by two pop can bottoms and a nut. Put metal scrubbing pad material in the space between the pots, this will assist with the heat radiation. Also added the metal plate to bottom of rod.

Step 3: The Build

Part 2 - Adding insulation and a stand

As this is an active heater where the heat will be extracted by a fan the heat has to be contained. This is accomplished by placing two cans around the outer pot and stuffing the void with fiberglass insulation.The stand is made from a piece of plywood with an aluminum dish on top. The legs are aluminum strips bent and attached to the wood. The heater stands on screws attached to the legs. The stand and heater are then attached together using bicycle wheel spokes. The little nuts on the spokes are left loose and fed from the bottom of the wood, the spokes are then bent and inserted into the holes in the can. The nuts are then tightened to secure everything.

Step 4: The Extraction Tube

The extraction tube is made up of 3 parts. The coupler, the hose, and the fan. For the coupler I used a tin can plus a tin can cap.The hose is shop vac hose, The fan is a computer power supply fan without the frame, it is attached to the hole thingy with epoxy. The hose attaches to the can with friction.

Step 5: Temperature Measurements

I lit the fire in the heater, took first measurement at 11:14AM, second measurement at 11:56AM, the third and fourth measurements taken with the fan running 12:00PM and 12:07PM.

The fan contributed to the increase in temperature by sucking in more air. The exhaust hair was warm but this could be improved by wrapping insulation on the hose to fight the cold air of the garage. As can be seen by the analog thermometer the temperature in the garage was about 10 degrees Celsius.

Step 6: Added Insulation Exhaust Tube

I wrapped insulation on exhaust tube, covered it with foil, went to the garage attached the tube to the heater, lit the fuel. Temperature in core 13 degrees Celsius, then 28, then 71, I stopped at 75. The air coming out of the fan was a lot warmer than the air was when the central core temperature was 150 degrees Celsius



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