How to build a smokeless fire.

With the winter chill setting in many of us will be burning wood.

We've discussed what to do with your wood ash previously. This time we want to talk about how to reduce the polluting smoke that's often a byproduct of us wishing to keep warm.

The bad news, wood smoke is harmful. It contains particulates which damage the lungs as well as poisons which are also harmful. In developing countries children's health is put at risk by open cooking fires - hence the drive to more efficient reduced smoke cookers.

But there is a simple way to reduce smoke emissions from our fires - whether your heater is open or closed.

First some basic science. When wood is heated it releases gases. First to be released is steam. Then flammable gases which are visible to us as smoke. So we need to think of a piece of wood as a "gas canister".

Traditionally we make a fire and light it from the bottom. We start with the smaller pieces and then these light the larger pieces at the top of the fire.

So what's the problem? Well, quite simply as the heat from the bottom of the fire heats the top pieces these release gases into the surroundings as smoke.

An alternative is the Top Lit Up Draft (TLUD) method.

Here we basically reverse the fire - an upside down fire - and reduce smoke.

So how does this work. In essence as the heat from the top fire heats bottom layers these release gases. But instead of rising unencumbered to the atmosphere the top layer fire simply burns these gases off.

Voila. Less smoke. Less pollution. And a more efficient process.

So when you're thinking about lighting a fire. Reverse everything you've learnt. And turn it upside down.

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