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A few notes before you start

1. These heaters will warm a small volume of air by a few degrees Celcius. More candles will provide more heat.
2. You'll need several heaters and a lot of candles if you intend using them to heat a whole greenhouse, even with secondary insulation (bubble wrap etc.)
3. If you intend keeping a whole greenhouse frost free, I would recommend some other type of heater - gas, electric or paraffin are some options.
4. The terracotta pots will get hot, then radiate the heat for a while after the candles have burned out - maybe 30 minutes or so.
5. If you use 8-hour tea lights, you will need to light some at sunset and a second batch around midnight during the winter months.
6. On the plus side, the heaters are relatively cheap to construct, and tea lights are readily available and inexpensive.
7. Note that the saucer does not get hot, and can be safely positioned on any stable surface, including an upturned plastic bucket.


Making a Heater from Plant Pots

Click thumbnails for larger images


Materials & Tools

4 nesting terracotta plant pots

One bolt

4 nuts

7 washers

3 tent pegs

1 terracotta saucer

8-hour tea lights


Step 1

Place a washer on either side of the drainage hole in the largest pot, and thread the bolt through. Thread a nut onto the bolt to secure it, but do not overtighten or you'll break the pot.

Step 2

Slot a washer, then the second-largest pot and another washer onto the bolt. Secure in place with a nut.

Step 3

Slot the third-largest pot onto the bolt followed by a washer and loosely thread on the nut.


Step 4

Place three tent pegs between the pots, spacing them evenly. Secure the pot with a nut, which should also trap the tent pegs in position.


Step 5

Slot a washer, then the smallest pot and another washer onto the bolt. Secure in place with the final nut. The assembly should now stand stably on the saucer.

Step 6

To use the heater, place one or more tea lights in the saucer and light them.



Photograph showing the nested pots from below.



A heater in my grow-house, ready to go. 

The grow-house is a plastic greenhouse erected inside my glasshouse. It has styrofoam insulation on the floor and holds containers of compost and water to provide thermal mass. My seedlings are on the upper shelf, which stays warmer. I also installed a reflective car-windscreen cover on the north wall of the grow-house to reflect sunlight and heat. Aluminium foil or an emergency blanket would also work well.    


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