Tag Archives: Wood

Wood Burning Properties

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A quick guide to wood burning properties

There are a many types of wood to choose from, all of which have their own burning qualities and properties. Although there are references to burning green wood here ; to get the most efficient and effective ‘burn’ in your wood burning stove, only very dry (at least <20% moisture) wood should be used. The following is a small guide only and is by no means comprehensive.

The table below shows the types of woods and their burning properties.

Alder Produces poor heat output and it does not last well. Poor
Apple A very good wood that bums slow and steady when dry, it has small flame size, and does not produce sparking or spitting. Good
Ash* Reckoned by many to be one of best woods for burning, it produces a steady flame and good heat output. It can be burnt when green but like all woods, it burns best when dry. Very good*
Beech* Burns very much like ash, but does not burn well when green. Very good*
Birch Produces good heat output but it does burn quickly. It can be burnt unseasoned, however the sap can cause deposits to form in the flue with prolonged use. Good
Cedar Is a good burning wood that produces a consistent and long heat output. It burns with a small flame, but does tend to crackle and spit and the sap can cause deposits to form in the flue with prolonged use. Good
Cherry Is a slow to burn wood that produces a good heat output. Cherry needs to be seasoned well. Good
Chestnut A poor burning wood that produces a small flame and poor heat output. Poor
Firs (Douglas etc) A poor burning wood that produces a small flame and poor heat output and the sap can cause deposits to form in the flue with prolonged use. Poor
Elm Is a wood that can follow several burn patterns because of high moisture content, it needs to be dried for two years for best results. Elm is slow to get going and it may be necessary to use a better burning wood to start it off. Splitting of logs should be done early. Medium
Eucalyptus Is a fast burning wood. The sap can cause deposits to form in the flue and can increase the risk of a chimney fire if burned unseasoned. Poor
Hawthorn* Is a good traditional firewood that has a slow burn with good heat output. Very good*
Hazel Is a good but fast burning wood and produces best results when allowed to season. Good
Holly Is a fast burning wood that produces good flame but poor heat output. Holly will burn green, but best dried for a minimum of a year. Poor
Hornbeam A good burning wood that burns similar to beech, slow burn with a good heat output. Good
Horse Chestnut A good wood for burning in wood stoves but not for open fires as it does tend to spit a lot.  It does however produce a good flame and heat output. Good (For stoves only)
Laburnum A very smokey wood with a poor burn. Poor do NOT use
Larch Produces a reasonable heat output, but it needs to be well seasoned. The sap can cause deposits to form in the flue with prolonged use. Medium
Laurel Burns with a good flame but only reasonable heat output. It needs to be well seasoned. Medium
Lilac Its smaller branches are good to use as kindling, the wood itself burns well with a good flame. Good
Maple Is a good burning wood that produces good flame and heat output. Good
Oak Because of its density, oak produces a small flame and very slow burn, it is best when seasoned for a minimum of two years as it is a wood that requires time to season well. Good
Pear Burns well with good heat output, however it does need to be well seasoned. Good
Pine (Including Leylandii) Burns with a good flame but the resin sap can cause deposits to form in the flue and can increase the risk of a chimney fire.MUST be well seasoned. Good (with caution)
Plum A good burning wood that produces good heat output. Good
Poplar A very smokey wood with a poor burn. Very poor
Rowan* Is a good burning wood that has a slow burn with good heat output. Very good*
Robinia (Acacia) Is a good burning wood that has a slow burn with good heat output. It does produce an acrid and dense smoke but this is of course not a problem in a stove. Good  (For Stoves only)
Spruce Produces a poor heat output and it does not last well. Poor
Sycamore Produces a good flame, but with only moderate heat output. Should only be used well-seasoned. Medium
Sweet Chestnut The wood burns ok when well-seasoned but it does tend to spit a lot. This is of course not a problem in a stove. Medium (For Stoves only)
Thorn* Is one of the best woods for burning. It produces a steady flame and very good heat output and produces very little smoke. Very good*
Willow A poor fire wood that does not burn well even when seasoned. Poor
Yew* A good burning wood as it has a slow burn and produces a very good heat output. Very good*

In addition there are also the compressed reclaimed ‘eco’ type of logs and briquettes which do tend to burn well and for a decent length of time because they are dense and very dry. You should try to choose a product that does not break apart too easily.
In a nut shell you should always use hard woods over soft woods.

Moisture Meters

The single worst predisposing cause of chimney fires today is wet wood. The recommended level of moisture is less than 20% to avoid chimney fires. You can read more about moisture meters in our site here. 

This guide was originally taken and adapted from http://www.flamingfires.co.uk/which-wood-burns-best.htm

Using a stove thermometer to ensure optimum efficiency

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Your newly acquired wood/multifuel stove will give months of long, easy & warm cosy days where you can lounge around just enjoying yourself. However, as with all things that are subject to temperature & pH variations, maintenance checks are essential.
Using a thermometer gives you peace of mind over safety and the satisfaction that everything is running under optimum conditions.

Often times these, “checks” may seem as if they might drag you out of your comfort zone but the good news is, that once you’ve attached it to the stove top (or flue pipe arising from it) using a thermometer is as simple as making regular readings. They come in a few varieties and can be wire, hose clipped or magnetically attached.

 

stove thermometer

Figure:1 Typical stove thermometer with “optimum operation zone”


Used primarily to avoid over firing, (the resulting extreme temperatures create bad fuel efficiency) and are operated by having an eye gauge in both °Celsius and Fahrenheit. Keeping your stove burning in the Correct range: 115°C – 245°C or  (240°F – 475°F) will ensure the safest operation, whilst simultaneously giving maximum fuel economy.

Running Too Cool

Allowing your stove to reach burning temperatures below 115°C or (240°F) will lead to incomplete combustion creating carbon monoxide, tar, soot and creosote.

Creosote itself, is a condensation residue of coal and/or wood particles, hydrocarbons, gases and other airborne debris. It is formed as gases cool, for example when air in a chimney is not hot enough to push the particles out. Its appearance is of a thick hard black shiny goo which is flammable and reduces the bore of the flue by sticking to it.

Running Too Hot

When you allow your stove apparatus to run above burning temperatures of 245°C or (475°F) you risk damaging your flue/liner/cowl and possibly warping your baffle plate.  The risk of chimney fires is significantly increased now, especially if there has been creosote build up.

Further Info

Choosing to read our other articles under ‘stoves’ or burning ‘wood’ to gain the knowledge needed to use your appliances to maximum efficiency under safe conditions is advisable. Please always remember a significant part of this maintenance strategy is to get your solid fuel heating appliances in use, swept at least once a year by your chimney sweep.

You can buy thermometers and wood moisture meters Here
NB/ We are in no way affiliated with this company and the link is only just to show an example of what items you may want

Moisture Meters

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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.