Frequently Asked Questions & Answers
Follow the link below to see our article 'Biomass heating: A renewables industry success story or an inefficient technology wasting public money?'.
In this article we address some of the negative issues raised by direct customer experience, the DECC report and in the media, and to offer some informed opinion and advice to anyone who is considering a biomass heating system for their business or home.
Biomass heating: A renewables industry success story or an inefficient technology wasting public money?
Q. What system would best fit my home and my needs?
A. Decide whether you require a whole house system or you just wish to heat a part of your house - i.e a sitting room. Consider how you can store the chosen fuel, fuel availability and how the different systems will fit into your own lifestyle. Take advice from professional equipment suppliers and installers who can give you detailed information about what will be right for you.
Q. How do I know whether to look for a boiler or for a stove?
A. If you wish to heat the whole house then you will need a boiler. If you wish to heat just one room for example, then you should consider a log stove or pellet burning stove.
Q. Do I need a chimney?
A. A log stove will require a chimney, whereas a pellet stove can be fitted into a room with just a flue to the outside.
Q. How much space is needed if I wish to install a stove?
A. Wood stoves come in varying sizes and you should get advice as to the right size of stove for your requirements. Most stoves would require no more than 1 sq. m. of space, including a heat
Q. Where do I store logs for my log burning stove?
A. A porch could suffice, depending on the amount of logs you wish to store. For larger quantities a log store or shed outside would be necessary. A log storage area should ideally be raised off the ground for underflow of air, be well ventilated and provide protection from rain.
Dry storage space is essential.
When deciding on where you are going to store logs, bear in mind how/where your logs are going to be delivered. Good, easy access to your log storage area will make life easier once your load of logs has been delivered. Likewise, it is preferable to have easy access from your log store to your stove, to reduce effort in re-fuelling your stove.
Q. Does using wood fuel give me a lot more work?
A. A log burning stove will require regular manual re-fuelling. You also need to ensure that you have regular supplies of good quality, ready to burn logs and are able to store the logs in a dry area.
An auto-feed boiler will automatically be fed from the hopper.
A pellet burning room stove may only require a few shovels-full of pellets per day - less work than carrying logs from a storage area to the fireplace.
Q. Are wood burning systems efficient?
A. Open fires are the least efficient method of burning wood - at probably only about 15-20% efficiency.
Modern wood burning stoves operate at around 70-80% efficiency and are very 'controllable'
Wood fuel boilers are more efficient at around 85 - 90% (note: these figures are offered only as a guide and there will be variations between different manufacturers' products and models)
Q. Can I use any wood in a boiler or a wood stove?
A. Unseasoned wood (i.e with a high moisture content) should not be used. It will not burn well, it will produce a lot of smoke, may do damage to your chimney and will certainly 'blacken' the windows of your wood burning stove.
Wood is ready to burn if it has 25% or less moisture content.
You should NEVER burn previously painted or treated timber.
Q. Where can I get good quality wood fuel from?
A. Ideally check that you can find a regular supply of the fuel you require in your local area, to keep delivery costs down
Your local stove retailer may be able to recommend some suppliers in your area.
Search on the Woodfuel Wales website supplier directory for suppliers in your area.
Research other supplier options through word of mouth recommendations, local advertisements etc. - but do ensure that the supplier can supply you with good quality, ready to burn fuel.
Q. Should I buy hardwood or softwood for my log burning stove?
A. Hardwoods are denser and therefore heavier, but they do have the same calorific value per Kg as softwoods. You would need twice the volume of softwood than hardwood, to obtain the same heat output, but softwood is cheaper to buy.
Hardwood burns more slowly than softwood.
If you have plenty of storage space, want to get your fire going quickly and don't mind topping the fire up more often, then softwood can be a cheaper alternative.
Q. What is a briquette and can I use them in my log burning stove?
A. A briquette is usually made out of dry sawdust, compressed into log or 'brick' shapes. They are generally supplied in bags of 10Kg. weight.
A briquette is heavier than a natural log of the same size due to its density and has a lower moisture content so burns more efficiently - at a higher temperature and for longer.
Briquettes can be used on open fires, but care should be taken as they expand as they heat and could fall out of the fire. Larger briquettes can be broken into 2 or 3 pieces before adding to the fire. They can also be used in log burning stoves and boilers.
They must always be kept dry or will tend to disintegrate and be unusable for burning.
Q. Once I have found my log supplier what questions should I ask them?
A. There are a number of questions which you should ask your potential supplier before agreeing to purchase:
1. Ask about delivery options:
Are the logs dumped at the gate, supplied in returnable bags; do they offer a service of stacking logs in your log store?
Are there any delivery charges, bag deposits or stacking costs?
Check that the supplier can provide logs of a suitable size for your stove or boiler - you can check the correct size with the equipment manufacturer. A standard log length is about 25cm and logs should be split to no more than 12cm diametre for efficient burning.
2. Understand what you are buying so that you can better compare prices:
Logs are sold by the 'load', in tonnes, loose cubic metres, stacked cubic metres or in small bags/nets. If you buy by the 'load' always ask what volume the load contains.
Always buys logs by volume, not by weight. Logs are heavier if they have a high moisture content, so you could be buying water if you buy by weight.
When buying by cubic metre, check whether it is a loose or stacked cubic metre. A loose cubic metre (when logs are piled at random) contains a third less wood than a stacked cubic metre (when logs are stacked neatly).
3. Ask what the moisture content of the logs will be:
A reputable supplier should be able to tell you what the average moisture content of the logs you are purchasing will be and should be able to demonstrate the moisture content to you when he delivers.
'Unseasoned' logs, also called 'green' logs, have a high moisture content (probably over 50%). These are not suitable for burning and will need to be stored in a dry storage area until their moisture content is down to 25% or below. This could take another 12 months. However, if you have available space to store these logs until ready to burn, it could be a good financial option as unseasoned logs are generally cheaper.
Q. What is so important about moisture content?
A. Moisture content is important because the more moisture (actually - water!) contained in the wood the less heat will be released to warm your home. The heat that is generated will be used to evaporate the water from the wood, which will create some steam, which will reduce the available heat even further.
A heavy log may not burn as well as a lighter log because the extra weight is due to a higher level of water. To burn efficiently wood needs to be dry or 'seasoned'.
Q. If I burn 'wet' wood does it really matter?
A. The wood will not burn efficiently so you will not get the benefit of the potential calorific value (heat) from that wood. It is costly to burn water!
Wet wood can also damage your system as tar will build up in the stove and flue and there will be a risk of chimney fires.
The glass on the stove doors will turn black.
Q. What is the correct moisture content for logs?
A. The industry quality standard is 25% moisture or less.
Fresh cut timber will have a moisture content of 50% and above.
Drying wood to 25% or below can almost double its heat output.
Q. How can I check the moisture content of my logs?
A. Purchase a moisture meter which will give you a guide as to the moisture of your logs. These meters are used by pushing the prongs of the meter into the split surface of a freshly split log.
Do not take a reading by inserting the prongs into the end of the log, or on the outside or bark of the log. The difference in moisture between the inside and outside of the wood can be as much as 15%.
If you do not wish to purchase your own meter, ensure your supplier will be prepared to randomly check the moisture of the logs he has delivered and to show you the readings from his own moisture meter.
Bear in mind that moisture content will vary depending on the storage facilities you have. If logs are left out in the rain after delivery the moisture content will rise and the logs may not be suitable to burn without some subsequent drying.
Another sign of logs being a little too wet to burn will be the 'blacking' of the windows on your stove.
Q. Where can I purchase a moisture meter?
A. These are readily available, either via the internet or from your local wood fuel equipment supplier. Prices vary enormously from £10 - 200+.
Unless regularly calibrated a meter is unlikely to be 100% accurate but they do provide a guide as to the moisture content.
Q. What are wood chips?
A. Wood chips are chopped up pieces of wood, ranging from 2mm up to 5cm in size, which can be supplied from forestry activities, clean recycled wood, arboriculture and factory waste.
They have a relatively low energy density and moisture content will typically be in the region of 25-30%.
They are usually supplied in bulk.
Q. Is a wood chip system suitable for residential use?
A. Not really. Wood chip is most suitable for medium to large scale boiler systems - in schools, large commercial buildings, hospitals or even large homes or estates.
These systems need large storage areas, good delivery access for bulk carriers and plenty of space for the boiler system itself.
Q. What are wood pellets?
A. Pellets are usually made from sawdust, compressed into small cylinder shapes and are similar in appearance to chicken feed pellets or cat litter.
They have an 8% moisture content and have a high energy density, compared with log and chip.
Pellets should have a consistent length, a smooth finish, should not fall apart easily and should comply to ENPlus standards. Poor quality pellets will break up easily, returning to dust and will not burn correctly- risking boiler shutdown.
Q. Are pellets suitable for residential homes?
A. Pellets can be used in single room heaters and will burn very efficiently. They can be purchased in bags, ranging from 10-20Kgs weight - making storage and handling relatively easy and clean.
They must be kept dry to prevent disintegration.
Bulk users can be supplied by lorry-load with the pellets being blown into a storage hopper with a fully automated feed system.