If you want a cheap way to keep the frost off in your greenhouse this winter, then this DIY heater could be the project for you.
Made using terracotta pots and a homemade candle or tealights, it gets hot and is cheap to run – what more could you want?
How To Make The Heater
The heater itself is really simple to make. You just need some terracotta pots, a saucer and some feet.
Pop the saucer on the ground and then place the three terracotta feet around the edge.
You then want to add your candle and light it now, as you will be covering it up soon.
This is a homemade candle that burns for days and costs 50p to make! Find out how I made it by reading on…
Now we put our biggest pot over the top; we want one roughly the same size as the saucer.
The feet keep it up off the saucer a little, allowing oxygen to be pulled in to keep the candle burning.
Now put another smaller pot on top of the larger one. The pots work as storage heaters, trapping the heat of the candle, making this design much more efficient.
I stopped at two pots, but you can add another even smaller one if you have it.
The soil is at 12.1 degrees Celsius, but the top pot is already 55!
Making A Candle
You can use tea lights with this design, and they do work. But I find making your own candle is much cheaper and also hotter!
I used a pack of lard for my candle as it was just 50p, but if you don’t want to use animal products, then a tub of veg shortening works just as well but is a little more expensive.
To start, you need to choose a suitable container for your candle and have a wick ready. I used an old tin can and some prewaxed wicks I bought off Amazon. You can also use string though, if you want.
Then you want to get your fat of choice melting, I do this at a low temperature to stop it getting too hot – we only want to melt it.
I then add my wicks to my coffee tin and also use a holder that came with them to hold them in place as the candle sets.
Then when it is all set up and ready you can pour the melted fat in, being very careful not to spill!
Now its in, it will need a good few hours to properly set and solidify.
I have made this candle before with a single wick, and it burned for 6 days and cost 50p to make. I imagine with two wicks, it will burn twice as fast but will be hotter; that’s my thinking anyway!
How Did It Work Overnight?
To find out how the heater actually got on overnight, I did a simple test. I have a few of the same greenhouse thermometers, so I put one outside and one inside. These thermometers record the lowest temperature they get to, so I can see how cold it got overnight.
It is the bottom number we are interested in. 7.1 Celsius, this is what the temperature got down to just outside the greenhouse.
Inside the greenhouse, it only got down to 10.1 Celcius, so we gained a few degrees with the heater. I would expect the greenhouse to be a little warmer overnight anyway, just because its a greenhouse and holds a little extra heat.
So the heater probably added around 2 degrees celsius to the inside temperature. I don’t think this is a bad result considering it costs next to nothing to run and can be built from garden pots you likely already have.
A couple of these in your greenhouse could make a real difference and keep the frost off for a while!