Moisture Meters

Moisture Meters

Readily available online from large retailers such Ebay and Amazon for around £20 , a firewood moisture meter is perhaps the best investment (next to a stove thermometer) and THE MOST IMPORTANT TOOL for helping you to get the most out of your stove.

Although there are many professional firewood suppliers out there who know their business and when they say that their firewood is well seasoned (sufficiently dry i.e. moisture content = 20% or less) it is what they say it is.
Unfortunately , there are also other firewood suppliers claiming their wood is seasoned , when in fact it is far from it. Your moisture meter will help to confirm that their wood is well seasoned and let you gauge exactly how wet it still is.
You may well find that some of the more professional firewood suppliers are booked solid , so it might be a good idea to get your orders in with them in advance of each season.

Problems burning Wet Wood (>20% moisture)

Without the use of a moisture meter the first you may realise that their wood is not dry enough , will be when you notice your stove isn’t giving out much if any heat at all and that the window is getting tarred up.
It doesn’t just stop there , burning unseasoned wood will tar up your chimney (increasing the risk of chimney fires) as well as reducing the life of your stove , liner and/or the whole chimney itself.

Burning unseasoned wood is inefficient , results in high levels of particulates , which is bad for your health , often makes NASTY problems for your chimney sweep and the environment as a whole !
(resulting in a government backed scheme ‘Burnright’ by woodsure is being promoted now in 2020/21).

In terms of how much heat you get out of your wood stove , the moisture content of your firewood is probably the single most Important + Controllable thing to consider. The moisture in the wood has to be boiled off before you get anywhere near the expected kilowatt per hour (Kw/h which is based on dry wood) rating which is why on so many levels not least financially , using a moisture meter is so important.

Buying Wood

Firstly , it makes sense to check with the supplier what type of firewood you are getting , although in a nut shell you should always use hard woods over soft woods. You can see the Wood Burning Properties of many types wood in our quick guide here. It may be well seasoned , or the supplier may only give you an assessment of the dryness of the wood anywhere from freshly processed to partly dry. When you have a firewood moisture meter then you can tell exactly how wet the firewood logs are , although of course there will always be other tell-tale signs i.e. no cracks in the end grain and a ‘wet’ smell.

Next time you get a firewood delivery from an unknown supplier take out your firewood moisture meter and before your supplier unloads , grab a couple of logs at random , split them in half with your axe and take a couple of moisture readings. If the firewood is well seasoned then it should have a moisture content of 20% or lower , a few logs at around 25% isn’t too bad as long as most of the load is under that.

                                     testing firewood moisture      
Picture 1: Moisture meter 

To take a moisture reading , all you need to do is push the two pins into your chosen piece of firewood. As you can see above in picture 1 , this piece of firewood is at 17% moisture which is ideal.

Anything under 20% is fine but nowadays you can get kiln dried wood which is around 11% and costs a bit more than normally seasoned wood.

If the firewood is a lot wetter than 20% , then it’s just a load of wet chopped logs that will one day eventually be seasoned firewood after you have dried & seasoned them yourself !!
If after using your moisture meter the wood turns out to be wet and the supplier is still claiming that it is well seasoned , you should either pay less for the wood (pays for your meter cost !!) and store it up until it is dry , or simply send it back.

Likely Stories

Of course it is possible that some firewood suppliers are not aware of the issues , or simply do not know how to properly season wood for wood burning stoves.
They often come armed with a multitude of freshly prepared stories to get you to accept their unseasoned wood and might say things like , “freshly felled wood is OK to burn straight away” (this is incorrect , will DAMAGE your equipment !! and cost you time , energy & Money ).
Another common story given to customers is , “because it has been a wet winter , it has been hard to season the firewood logs properly”.

In our own experience , customers have reported some kiln dried log loads ranging from the expected 11% all the way into +40%.

However , seasoning firewood properly and then delivering the properly seasoned wood , is basically their job description and so you should hold fast against accepting these fairy tales.  

Seasoning your own wood

You can also use a firewood moisture meter to see how well/quick your firewood is seasoning , which stacking techniques work best etc.
Crisscross stacking with air gaps works faster and more efficiently than pyramid piling. When you are processing and seasoning a lot of firewood , it really makes sense to do it in the most effective way possible.

Firstly , to properly season firewood the wood must be cut into short log lengths , typically 25 cm and then split down the middle to increase the surface area and aid the drying process. Log diameter should be typically 5-15 cm and a range of sizes is perfect. The split logs need to be stacked under cover , with max airflow around the stack.

How long the logs need to season will depend on the species e.g.  Ash might require 12-18 months whereas Oak will probably need closer to 3-4 years to get really dry and down to below 25% moisture.

Taking a meter reading

To take an exact moisture reading you need to measure the moisture on the inside of your piece of firewood: the firewood will be drier on the outside where the wind and sun have had their effects. So split a piece of firewood down the middle , push the two pins on the end of the moisture meter into one of the freshly split faces of the wood (not the end grain and not the outside faces of the wood) , ideally near where the middle of the piece was before you split it and press the On button. The moisture reading will appear on the screen as a percentage.

Kiln Dried Wood

Kiln drying is a process of force drying which can be done within anything from 60 hours to a week , depending on the type of drying process.  Drying wood this way virtually sucks the moisture out of the log , right from the centre. One thing you will always find with kiln dried logs , unlike really well seasoned logs , is that there will be more of a gradient in moisture content across the log. Kiln dried logs usually show 10-15% on the outside and 20-25% on the inside , with the overall average below 20%. In contrast , one would expect to see more consistent moisture content throughout the log when really well seasoned.

In summary unless you have tested that your seasoned logs are properly dry using a moisture meter correctly , then kiln dried logs are probably a more expensive but convenient alternative.

Be aware that there are many new kiln dried log suppliers, so try and make sure they carry the Woodsure and/or HETAS quality assurance certification for guaranteed quality.