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How to heat a room with a candle (or a few candles and flowerpot)? or not?6 min read

How to heat a room with a candle (or a few candles and flowerpot)? or not?6 min read

After I published my previous article on how to efficiently heat the basement, and after reading the post, someone posted this questions to me.  Why did I not address the absolute cheapest method – “How to heat a room with a candle (or a few candles)?”.  This is a response post.

If you’re living in this world, you would have heard this in the last few years or have read a blog post or seen a video clip.  It almost became viral and I am still seeing this method floating around the web.

Can we heat a room with some candles? or is it a myth?

To answer this we need to understand a bit about energy and heat.

  1. We only generate heat by burning or converting one form of energy into another.
  2. Amount of heat that can be utilized is the maximum amount of heat that we can generate.

So, with this basic premise let’s analyze.

Heat is mostly measured in the traditional unit of measurement called the British Thermal Unit (A.K.A. BTU)

Definition of BTU: Amount of heat needed to raise a pound of water by one degree Fahrenheit.

What’s convection vs radiation?

Convection heat transfer happens when a liquid or gas particle transfers the heat as they move.  The candle heats up the air and the hot air rises thereby heating the room, albeit by a very small amount.

Radiation heat transfer happens when an object that’s warmed up emits electromagnetic waves.  The other objects that come in the way of the electromagnetic wave get the heat.

The Candle-flowerpot heater setup

  1. Flowerpot over candle to heat a room on the cheapLight up a few candles
  2. Invert a ceramic or a terracotta kind of flower pot.
    • Note:  Please do NOT use a plastic one that looks like a mud pot. 
  3. Keep some object between the base and the flower pot opening.
    • This space is needed to provide oxygen for the fire to burn
    • The gap will also suck the cold air from below as hot air rises.
  4. Leave the hole on the bottom of the flower pot open.
    • This will let hot air rise and escape through the hole, pulling cold air from below and heating more air

I have also seen more pots added and several different versions of it.

So, How to heat a room with a candle? Is it possible?

Yes, but by only a very little.  Just by the amount of BTUs that a candle can produce, multiplied by how many candles we use.  Not more. Not less.

We also have other issues such as loss of heat, which is what we concentrate on when talking about efficiency.  So the idea is to generate any heat possible and not spend unnecessary energy and prevent loss of heat. That’s the genesis.

Here with this method, some of the energy will be lost in producing the light, and only some will go into producing the heat.

The thesis behind the flowerpot-candle heater

Diy Candle and Flowerpot heater airflow and heat transfer diagramThe bunch of candles you burn produce heat.  The heat generated is then going to heat up the air.  The air then circulates to warm up the space.  That’s easily known.

Because of this setup we have, the air will also heat the ceramic pot while on the way out, at the top.  Secondly, the light is trapped and that converts to more heat, by heating up the flowerpot.

The flower pot then radiates the heat making the room warmer.

So in effect, just a candle will only be transferring heat through convection.  Using a flowerpot also radiates and so more heat is produced.

How much heat does a candle produce?

I haven’t verified the exact BTUs or wattage that a candle produce.  It didn’t excite me that much to spend any more time. However, for this post, I am going to refer to a reliable source and use the measurements provided.

Here is a handy-dandy BTU calculator.

To heat a very small closet ( a 3 x 5 space) and increase by 1 Fahrenheit, you need 70 BTU per hour or 20 watts.  That is assuming normal North American insulation, so the loss of heat is very minimal and gradual.

I am seeing a wide range of values online for how much heat does a candle produce. Some say 30 watts and others 70 watts.

In any case, the wattage is the total output and you have to subtract the amount of energy that escapes as light.  Since candles produce some decent amount of light, the heat produced will be somewhere in the 40 watts range.  This is a pure guess, don’t quote me on that.

The big question – Will it Heat or Not?

multiple flowerpot-How to heat a room with candlesIt’s a myth and wouldn’t heat as much, per the thesis.

Why?

Because you can’t multiply heat.  Heat is an energy form.  And we know energy can’t be created or destroyed.  It can only be transferred.

If the air is hot, and when it touches the inside of the flowerpot, the heat exchange happens and making the pot warm and the air loses the heat.

However, since the pot becomes somewhat warm, we can definitely notice some radiation from the pot.

This creates an illusion as if there is more heat being radiated.  In reality, the total amount of heat produced by the candle is exactly what is being felt outside.

With just the candle, we would have had all the heat just by convection.  Using a pot, some of the generated heat generated will come out as a radiation.

People started taking this to a whole another extreme and started piled pots in their setup. So far I have seen someone went so far as to stack four pots. The image is from a lady who stacked four pots to increase the amount of heat that it produces.

Risks and bad effects due to candle heat

First, it’s risky. Very risky.  You lovely cat can smack it and the whole room will be a disaster. Home fire will surely get the cold out, but that’s going to be a costly heating exercise.

Second, the carbon monoxide and other toxic gases as released indoor and there is no way to vent it outside, compromising your indoor air quality.

My Final Thoughts

The amount of energy produced is negligible from a few candles. You need lots of them and eventually, you will end up making a fireplace (with no chimney).

It’s a hype, I wouldn’t buy into it.  Ignore the clever trick.

Forget firepot and a few candles. Instead, get thermals, put on several layers of clothing, insulate your room and look for an energy efficient heating source.

Oh wait, for some, it definitely heats up the mood.  That is if you’re romantic.  I love candles and the visual appeal, so heat your partner up and not the room ;).

 

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