Wood Moisture

You often read or hear people mentioning about wet wood and not to use it in your fire or stove. But what does this mean? Understanding what wood to use on your fire or in your stove will help to reduce emissions, prolong the life of your flue or stove, create more heat and reduce costs.

How does a fire work? Combustion of wood fuels

For combustion to take place, there are 3 basic conditions that are needed,

Oxygen + Fuel + Heat = Combustion For combustion to begin the fuel must reach a sufficient temperature to enter it's combustible gas phase. To do this the fuel must be heated past its ignition point. When the combustion temperature is reached, the compounds and molecules within the fuel break and recombine with oxygen in the combustion air. It is this process which will release the chemical energy in the fuel as heat and light energy. Once the combustion temperature is reached, the chemical reaction becomes a self sustaining reaction producing more heat than it needs to sustain itself. If the combustion temperature is not maintained throughout the life of the fire, the chemical reaction between the fuel and the combustion air is incomplete and emissions are produced. Excessive emissions are caused by low burning temperatures which can be attributed to poor fuel quality, inefficient ventilation, poor system design and poor burning practices.

What should your wood moisture be?

For firewood that is for use in a domestic stove the moisture content should be below 20%. In my opinion, the closer to 10% the better. Effects of wood with a higher moisture content

• Lower temperature / inefficient burn

• Higher emissions / pollution - excessive smoke

• Blackened glass on stove

• Harder to light

• Can damage flues

• Creosote build up

Using wood below 20% moisture

• Reduce environmental impact

• Easier to light

• Less smoke

• Cleaner burn

• Less deposits on stove, glass and flue
  

How does the moisture affect the fire?

If you are using wood that has a higher moisture content, the fire will use it's energy to burn off the moisture, lowering the temperature of the fire causing incomplete combustion which then creates higher emissions.

How do you tell if the fire is burning hot enough?

It can take between 15 - 30 minutes maybe longer for your fire to reach optimal temperature depending on the stove and the fuel that is used.

Once the fire is fully established, you will notice that the soot deposits on the glass and on the fire bricks will start to burn off and there will be little to no smoke visible. The most effective way to get a guide of the temperature is to use a stove thermometer.

Ready to Burn Scheme

Under the Air Quality (Domestic Solid Fuels Standards)(England) Regulations 2020, wood fuel sold in volumes under 2m³ must be certified as Ready to Burn.

Ready to burn firewood has a moisture content of 20% or less.

Where to find a wood supplier

You can find a supplier on www.woodsure.co.uk by entering your postal code.

Although most suppliers do their best to keep the moisture below 20%, the weather can have an effect on the woods moisture content.

I would advise to test the wood delivered from a supplier to make sure you are getting what you have paid for.

How to tell if your wood is dry enough?

There are a few ways to check the wood to see if it is suitable to burn.

Visually - Check for cracks in the ends of the logs, a hollow sound when knocking them together, loose bark and lighter in weight.

Moisture Meter - Although the above method is an easy quick check, it is not that accurate. For better accuracy I would recommend a moisture meter.

How to test logs with a moisture meter

1. Select a few logs from across your log store.

2. Split log down the middle if it is not already split.

3. Measure across the grain. Insert the meter pins firmly into your wood to get the most accurate reading.

Having the correct moisture level in your logs is important to keep your fire burning hot, which will reduce the environmental impact, can prolong the life of your heating appliance and flue, save you money as dry logs will burn more efficiently meaning less logs required to create heat and reduces the chance of blockages form creosote build up.

Always maintain your chimney and stove by getting it swept and serviced annually (dependant on fuel and amount of use), refer to the manufactures recommended service intervals for your appliance.

A stove is only as good as the wood it burns.

References: Woodsure, Chimney Skills Training Ltd, Ready to Burn