Firewood Moisture Content

What Moisture Content Firewood Should Be (And How To Check)

In Firewood, Indoor Fireplaces, Multi Fuel Stoves, Wood Burning Fireplaces, Wood Burning Stoves by James O'KellyLeave a Comment

An important aspect of having a fire in any type of fireplace, whether it’s an open fireplace or wood burning stove, is to ensure that the firewood is dry enough to use.

For wood to burn efficiently on a fire it needs to have a low enough moisture content, so what moisture level should firewood be?

For firewood to burn efficiently it should have a moisture content of 20% or lower. As the moisture content of firewood increases above 20% it gets progressively harder to burn effectively in a fire.

So how do you know whether firewood is dry enough, how can you measure moisture content in firewood, and can firewood be too dry? We’ve explained moisture content for firewood in much more detail below.

What Moisture Level Should Firewood Be?

Many of the issues associated with poorly burning fireplaces or stoves can be the result of burning wood that is too wet. These issues can include wood that isn’t:

  • Catching alight properly
  • Burning efficiently
  • Generating much heat
  • Burning without producing smoke

You may also notice that wet wood also makes hissing and spitting noises as the fire tries to burn off the excess moisture. Wet wood is harder to burn because more energy is required by the fire to burn of the excess moisture before it can start to efficiently burn the wood.

Freshly cut wood can have a moisture content of anything over 20%, meaning that this ‘green’ wood is very high in moisture content and would struggle to burn on a fire.

Green Wood Moisture Content
The moisture content of green wood is too high to be used as firewood, and will struggle to burn efficiently on a fire

The time of the year that the wood is cut can also determine how high the moisture content of the wood is. Wood cut in the winter months will typically have a lower moisture content than wood that is cut in spring.

This is important because for wood to be useful as firewood then it needs to have a moisture content of under 20% to burn efficiently.

To achieve this moisture content the wood needs to be dried out, through a process known as seasoning.

The higher the moisture content of the wood when it’s cut, the longer it can take for it to dry out to recommended firewood moisture content levels. Cutting wood when it’s already low in moisture content as possible can help to speed up the drying out process.

Seasoning wood can be a lengthy process. Certain hardwoods can take up to 2 years to dry out, while softwoods can typically take up to 1 year.

Hardwoods such as Ash or Oak are from deciduous trees, which typically take longer to grow compared to softwoods such as Pine, from coniferous or ‘evergreen’ trees.

The slower growing process of hardwoods can mean that the wood grows more densely, meaning that the seasoning process can also take longer as a result.

Although the seasoning process for firewood can take a long time, almost no involvement is required once it has been setup.

To ensure that wood dries out in the most efficient way, and to prevent it from rotting, the wood should be:

  • Stacked on top of some sort of impermeable ground, such as concrete, to ensure that moisture from the ground doesn’t seep up into the wood, and for any excess water to runoff into the nearby ground.
  • Located under some sort of canopy, to help shelter the wood from the majority of the rainfall throughout the process.
  • Open on one side to allow the weather to help dry out the wood, in particular the wind.

The wood also shouldn’t be directly covered over by anything, such as sheet of tarpaulin, as this can trap the moisture and cause the wood to rot rather than dry out.

We season our own firewood to be used in our wood stove, and the picture below shows how we arrange the wood so that is dries out effectively.

The seasoning process, where wood is left to dry before it can be used as firewood

You can read more about how we season our own wood here.

As the conventional seasoning process can take many months or even years, a process known as kiln drying helps to vastly speed up the drying process of firewood. High moisture content wood is simply placed in an oven-like chamber where the excess moisture content is evaporated off.

You’ll typically find that bags of logs or kindling bought from your local store will have been kiln dried as stated on the bags.

Kiln Dried Hardwood Firewood Bag
A typical bag of kiln dried logs
Kiln Dried Kindling Bag
A typical bag of kiln dried kindling

How Do You Know If Firewood Is Dry Enough?

Dry firewood ready for burning looks a lot different to wood that is freshly cut and high in moisture content.

The table below highlights the main differences between wet and dry wood

  Dry Firewood Wet Firewood
Color Brown Greenish tint
Weight Lighter Heavier
Looks Rough texture Smoother texture
Condition Bark peeling & cracks Softer bark & wood

In summary, you can tell whether firewood is dry enough if the wood is:

  • Brown with no hints of green.
  • May be splitting at the ends with cracks forming.
  • The bark can be coming away or is easier to peel off.
  • Can make a hollow sound when pieces are hit together.

The images below show what you can expect a dry piece of wood to look like.

Dry Firewood
What you can expect a log to look like that’s dry enough to be used as firewood
Dry Firewood
The bark may be peeling off on dry firewood
Dry Firewood
The ends of a dry piece of firewood can look rough and can be splitting or cracking

Ultimately the best way to get an accurate reading as to whether firewood is dry enough is to use a moisture meter.

A moisture meter is a handheld device that can be used to accurately measure the moisture content of any wood by giving a reading when pressed against it.

Moisture meters will typically have two metal pins that stick out the top (although some models of moisture meter can be pinless), and will also have a digital screen on the front that will give you an accurate reading to typically one decimal place.

Here’s what our moisture meter looks like:

Moisture Meter
A typical moisture meter. This is the one we use

In many cases wood can be sold in bags as ‘seasoned’ wood but the actual moisture content of the wood isn’t low enough for it to burn efficiently.

A study by the University of Tennessee (which can be found here) showed that a typically bag of ‘seasoned’ wood had moisture content values ranging from 50-90%, which is far too high to burn efficiently. The study concluded that low moisture content is key for firewood, and that the best approach is to buy and further season the firewood well before it’s needed.

We bought a bag of ‘kiln dried’ kindling and logs from our local store and used our moisture meter to find out what the actual moisture content of the logs actually were.

The bag stated that the logs were ‘less than 20% moisture content’.

Kiln Dried Firewood Moisture Content
The bag of kiln dried firewood we had at the time stated that the wood would have less than 20% moisture content

The moisture readings of a random selection of the logs were found to be too low for our moisture meter to read, meaning that the moisture content of these kiln dried logs was less than 6.8% (the lowest reading our moisture meter takes).

Firewood Moisture Content
In fact, the firewood was so dry that our moisture meter couldn’t give a reading

By checking these pieces of wood we’ve ensured that we’re not burning any wood that is too high in moisture content, which could have lead to problems being able to start the fire and keep it going.

How To Measure Moisture Content In Firewood

In order to correctly measure moisture content in firewood you’ll need to have a moisture meter.

A moisture meter is a simple-to-use tool that gives you a very accurate reading of moisture content in firewood.

To measure moisture content in firewood:

  • Remove the end cap of the unit to reveal the pins, unless it’s a pinless moisture meter.
  • Turn on the moisture meter using the on/off button on the unit.
  • Gently push the two pins at the end of the moisture approximately 1mm into the piece of wood.
  • The moisture meter will give a reading as to the moisture content of the wood.

How to measure moisture content in firewood is explained in more detail below using our own moisture meter as an example.

If you have a pinless moisture meter then you’ll need to remove the part that covers the pins at the top end of the unit.

Moisture Meter
Take the end of the moisture meter if it has one

With the cover removed the pins are now available to be used to read the moisture content. You’ll also need to turn the moisture meter on before using it.

Moisture Meter
Turn on the moisture meter and make sure it’s on the wood setting

To read the moisture content of any piece of firewood, simply place the two pins against the wood. Both of the pins need to be touching the wood for the moisture meter to provide a reading.

The Environmental Protection Agency (EPA) recommends that:

  • To ensure that you’re testing the inside of the wood, moisture reading should be taken on any newly split sides of wood.
  • The prongs on the moisture meter should run parallel with the grain when testing.
  • 2-3 tests should be done in different locations to ascertain the overall moisture content of any piece of wood.

Your moisture meter will then give a reading on the digital display as to the exact moisture content of that piece of wood.

Moisture Firewood
Press the pins against the wood to get a moisture reading

The display on our particular model of moisture meter also lights up in either green, orange or red depending on the moisture content of the wood it’s reading.

In general, the lower the moisture content the better, and in the case of our moisture meter, it lights up green for moisture contents up to 15%, amber for up to 20% and red for any firewood moisture readings of over 20%.

As the seasoning process can take such a long time, the EPA recommends that firewood with a moisture content of between 15% and 20% is most efficient for burning.

Ensuring that wood is dry enough to burn is essential for having a fire in your home that burns efficiently and effectively. Moisture meters are therefore an essential piece of kit for any type of fireplace or stove that burns wood.

If you don’t already have a moisture meter then we highly recommend looking into getting one. They’re an inexpensive purchase and will help to reduce a number of issues associated with burning wood that is too wet.

You can see our current favorite moisture meter over on Amazon here.

If you’re in the UK you can see our particular model of moisture meter over on Amazon here.

Can Firewood Be Too Dry?

For firewood to burn efficiently on a fire it needs to be as dry as possible, but can firewood be too dry or too well seasoned?

Wood can be too dry to burn efficiently on a fire, but it’s not common to find a piece of wood that’s too in low moisture content that it would burn too fast on a fire.

Wood that is too dry can produce more smoke than wood with a slightly higher moisture content of between 15 and 20%, which is regarded as the target moisture content for all firewood.

Wood won’t naturally dry out so much that is becomes too dry, as the humidity will always mean that there’s moisture within the air and prevent firewood from drying out too much.

We’ve had a few pieces of wood in our home that we haven’t got round to burning and that have been inside for over two years.

Taking a reading of the moisture content of these logs showed that the moisture content was around 10%.

Moisture Firewood
Moisture Content Firewood

Further Reading

How A Fireplace Works

Parts Of A Fireplace Explained

How A Wood Burning Stove Works

How To Use A Wood Burning Stove

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