DIY Greenhouse Heater

This DIY Greenhouse Heater Gets Hot!

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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.

Terracotta Saucer and Feet
Terracotta Saucer and Feet

Pop the saucer on the ground and then place the three terracotta feet around the edge.

Add Your Candle
Add Your Candle

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…

Stack a Pot On Top of The Feet
Stack a Pot On Top of The Feet

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.

Stack Another Pot On Top
Stack Another Pot On Top

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.

Soil Temperature
Soil Temperature

The soil is at 12.1 degrees Celsius, but the top pot is already 55!

55 Degrees!
55 Degrees!

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.

Block of Lard In A Pan
Block of Lard In A Pan

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.

Old Coffee Can With Two Wicks And Holder
Old Coffee Can With Two Wicks And Holder

Then when it is all set up and ready you can pour the melted fat in, being very careful not to spill!

Pour The Lard In And Let It Set
Pour The Lard In And Let It Set

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.

Temperature Outside Overnight
Temperature Outside 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.

Temperature Inside Overnight
Temperature Inside Overnight

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!

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One Comment

  1. I loved doing this last winter
    But there needs to be some fire warnings given.

    The greenhouse needs to be stable. If risk of blowing over need to on bricks. For stability.

    Bungee cord to fence or tied down in case of strong winds

    Beware using lard as it burns animal fats and dangerous to breathe in
    Trex or veg oil based products are safer

    Thinner wicks result in lower flame and can go out

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