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Wood Burning Properties

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. Wood always burns best on a bed of its own ashes, the following is a small guide only and by no means comprehensive.

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. However, you should try to choose a product that does not break apart too easily.

The table below shows the types of woods and their 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*

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 here >(Moisture Meters)

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

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Using stove thermometers to ensure optimum efficiency

Using stove thermometers to ensure optimum efficiency

Using 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 variations, maintenance checks are essential giving you peace of mind and satisfaction everything is running to optimum conditions.

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

ChimGard Stove Pipe ThermometerFigure:1 Typical stove thermometer (with orange goldielocks zone)

They are used primarily to avoid over firing, the resulting extreme temperatures created and bad fuel efficiency. Operated by having a eye gauge in both °Celsius and Fahrenheit. Keeping your stove burning in the Correct range of 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 reduces the bore of the flue by sticking to the inner bore.

Running Too Hot

When you allow your stove apparatus to run above burning temperatures of 245°C or (475°F) you risk damage; warping your grate and also to your flue/liner/cowl too.  A significant increase of the risk of chimney fires is created, especially if there has been creosote build up.

Read our other articles under ‘stoves’ or burning ‘wood’ to get all the knowledge you need to use your appliances to maximum efficiency and safety. Also Please remember to get your solid fuel heating appliances swept at least once a year by your chimney sweep.

You can buy thermometers and wood moisture meters here Here

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Moisture Meters

Moisture Meters

A firewood moisture meter is perhaps the most important stove tool for helping you to get the most out of your stove.

Your firewood moisture meter can help you make sure that you are getting well seasoned wood. Although there are many firewood suppliers out there who know their business and when they say that their firewood is well seasoned it is. You may well find that some of these more professional firewood suppliers are booked solid; so you should try to get your orders in with them over the summer. Your firewood moisture meter will help to confirm that their wood is well seasoned and let you gauge exactly how well seasoned it is. Conversely; there are also firewood suppliers out there who supply firewood, claiming it is seasoned, when in fact it is far from it.

Without a moisture meter the first you may know that their wood is not dry enough may well be when you notice that your wood burning 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 wood burning stove, liner and/or chimney flue itself. Burning unseasoned wood is inefficient and results in high levels of particulates, which is bad for your health and often makes NASTY problems for your chimney sweep.
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 thing to consider, (the moisture in the wood has to be boiled off before you get the expected kilowatt per hour rating-which is based on dry wood) which is why a firewood moisture checker is so important.

Firstly it makes sense to check with the supplier what type of firewood you are getting (see wood burning properties here (Wood Burning Properties), it may be well seasoned, or the supplier may give you an assessment of the dryness of the wood anywhere from freshly processed to partly dry. If you have a firewood moisture meter then you can tell exactly how wet the firewood logs are, although of course there will be other tell-tale signs i.e. no cracks in the end grain and a ‘wet’ smell.

Buying Wood

Next time you get a firewood delivery take out your firewood moisture meter and before your supplier unloads, grab a couple of logs, split them in half with your axe or hatchet 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, this piece of firewood is at 17% moisture which is ideal. You should aim for around 16-17% moisture for firewood which is easy enough to achieve.

If the firewood is a lot wetter than this, then it is not actually seasoned firewood; it’s just a load of wet chopped logs that will one day be seasoned firewood after you have dried & seasoned them yourself 🙁 . If after having used your firewood moisture meter the wood turns out to be wet and the supplier is claiming that it is well seasoned, you should either pay less for the wood and store it up until it is dry, or send it back.

It is possible that some firewood suppliers are not aware of the issues, or 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 that freshly felled wood is “Ok to burn straight away” (this is incorrect !! ) or that it has been a wet winter and it had been hard to season the firewood logs properly. However,  seasoning firewood properly and then delivering  it, is basically their job description and you should hold fast against accepting these fairytales.  

 Seasoning your own wood

You can also use the firewood moisture meter to see how well your firewood is seasoning, which stacking techniques work best, etc. When you are processing and seasoning a lot of firewood it really makes sense to do it in the most effective way possible. For example, it is possible using a small, a single log thick, stack of firewood on a south facing section of wall to drop the moisture from around 55% when first felled, to around 17% in around 4 months!

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.
Just an example you can find Stihl Wood Moisture Meter Customer Reviews on Amazon here > http://www.amazon.co.uk/product-reviews/B004NQ0RL4
Remember as linked to in paragraph 3 above some wood burning properties can be see here in another of our wood category posts here. (Wood Burning Properties)