A-Z of Wood Pellet Heating

There’s plenty to learn about wood pellet heating, and that’s why we’ve put together this A-Z of Wood Pellet Heating.

A – Automatic ignition

Most wood pellet boilers for domestic use have automatic ignition. This means that when heat is not needed the boiler can turn itself off. It can self ignite when there is a need for heat. These are service items and will wear out over time e.g. 3 years, and are easily replaced during a service visit.

Hoppers that do not have automatic ignition have a low burn or stoking mode where the embers of the pellets are kept alight. This does mean that extra fuel is used, but the benefits may be a cheaper boiler.

A – Ash, Ash chamber and maintenance

All wood pellet boilers produce ash. The smoke containing the ash goes from the pellet burning chamber or bowl through the heat exchangers before being removed through the flue.

With no automation the boiler owner is required to clean the burner bowl every 2-4 weeks and also clean the heat exchangers by rodding or a semi automatic rodding device. The flue also needs ash emptying on a monthly basis and sweeping annually.

Some boilers do contain automation that reduces the need for ash cleaning.

B – Biomass

Biomass is strictly the weight of living biological organisms within an ecosystem. It has been adopted as a collective name for fuel that has been grown e.g. wood, miscanthus, straw, pine nut kernels, palm oil.

For homes wanting the Renewable Heat Incentive biomass alternatives are wood gasification and wood pellet boilers. Larger systems (above 45 kW) that may include a wider variety of fuels will have to be approved by Ofgem.

B – Burn Chamber

A burn chamber is where the pellets are fed and burnt. Some burn chambers are round and some are open. Some are supported by automatic ignition and self cleaning.

C – Carbon Emissions

Carbon dioxide emissions are part of the cause of global warming. Space and water heating in homes makes up 70 percent of all emissions from the home in the UK.  If you are trying to reduce your carbon emissions this is the place to start. Either use less heat or use heat that has been produced from a low carbon source such as wood pellets!

D – Density of Wood Pellets

Wood pellets are very dense as they have been compressed. Compared to wood chip this means that you need less storage (perhaps 3 times) for wood pellets.

You know how many wood pellets you need to buy and what space you need to store. The transport cost is also lower.

D – Dusty wood pellets

Good wood pellets are not dusty. Buying your wood pellets from a trusted source that conforms to wood pellet quality schemes ensures (E.g. Hetas, or Woodsure) that you do not get the increased maintenance problems that may result.

E – Energy of wood pellets

Wood pellets produce about 4800 kW per tonne. If the average house needs 20,000 kWhs a year then 4-5 tonnes of wood pellets will be sufficient.

Heating oil generally delivers 10 kWhs per litre. The same house would need 2000 litres of heating oil.

F – Fuel supply

Wood pellets are an alternative to gas and oil as a fuel to heat a property. Currently wood pellets are cheaper to purchase than either gas or oil and come with the knowledge that there are lower carbon emissions that result.

The fuel is normally supplied in small bags (easy to carry e.g. 10kg or 15 kg), 1 tonne bags, or blown from a lorry into a large hopper or silo.

You can purchase wood pellets from a number of places. The best place to start is often the manufacturer where they will either organise themselves or have a directory of partners that they work through.

Your installer will have good experience of using wood pellets and they may also know how best to organise deliveries.

You can buy pellets at country stores in bags and this ensures that you would not run out.

F – Flue

All wood pellet boilers have a flue to take the gases of combustion out of the building.

Flues can be traditional chimneys from existing fireplaces. These suit attractive boilers such as MCZ or other similar Italian boilers. Your chimney should be checked for suitability with respect to the building regulations. This may mean that a liner has to be installed.

If you have not got an existing chimney or flue it is common to install twin wall flues that probably go on an outside wall and up to above the height of the eves. Internal flues can also be installed, but will need additional measures to ensure that they are not near to any combustible materials.

The flue needs to be sited so that it does not blow emissions through a neighbours window – and that it is sufficiently high to create enough draught to take the gases away from the boiler. A height of 4.5m is recommended as a minimum unless a suitable calculation can be provided.

G – Grants 

Wood pellets are a renewable and low carbon fuel. Increased adoption of them will help the UK to reduce its carbon emissions and reduce the UK’s impact on global warming.

The Renewable Heat Incentive is an incentive rather than a grant and is a payment based on heat need per annum rather than a grant to install. For further information please see our RHI page.

For domestic installations the government has introduce Renewable Premium Payments. This will be £950 for wood pellets and available for installations until March 31 2012.

H – Heat Exchange

When pellets burn they create heat. This is circulated within the boiler through tubes (which may be self cleaning) that in turn heat water that is circulating.

Heat exchange is used to provide heat to rooms through radiators or underfloor heating.

Heat exchange is used to make domestic hot water through passing the hot water from the boiler through a tube running through a hot water tank. This tube heats the water in the hot water tank.

H – Hetas

Hetas is the solid fuel body and an accredited assessor for MCS accreditation and competent installers.

“Competent” installers should have been through training to install and had an inspection of an installation.

Many installers will therefore refer to their Hetas training and accreditation in the form of a badge on their van or paperwork.

It should be noted that Hetas are not the only source of training and accreditation. There are a number of MCS accreditation bodies who each have their own competent person scheme. Details are currently emerging (October 2011) as to what these are.

If in doubt do ask your installer.

H – Hopper

A hopper is used to store wood pellets. This may be internally ie part of the boiler, or externally as a separate fuel store.

If you are tight for space then a boiler with an internal hopper may be for you. You would have to manually feed pellets into the hopper probably 2 or 3 times a week when it is really cold.

If you have lots of space you can have a large fuel store and benefit from bulk discounts and hand feeding your boiler. Your installation costs will be higher.

I – Ignition

A traditional biomass boilers might be a wood boiler with a back burner. This is lit with matches and either paper or similar fire starting catalyst.

Most multi-fuel and wood boilers also use this method.

Many wood pellet boilers have automatic ignition linked to a thermostat or boiler programme. This saves you time and inconvenience.

 J – Building Regulations Part J

Any installation of a wood pellet boiler must comply with Building Regulations Part J. As part of MCS accreditation installers can sign up to a competent persons scheme that means that they can sign off an installation. Equally Hetas courses for biomass can be used for a sign off without MCS accreditation – your installation will be perfectly valid with this, but you will not be eligible for the RHI (Renewable Heat Incentive).

If your installer cannot sign off your installation they can contact building regulations and pay a fee (perhaps £150) for an inspection and sign off.

Key issues raised by building regulations are:

The hearth – sufficient distance from the edge of the hearth to the boiler

The flue – size and siting

Ventilation of the room

Combustible materials and proximity to either the flue or the boiler

K – Kilowatts (kW) Kilowatt hours (kWh’s)

Kilowatts (kW) is a measurement of heat and is used to rate how much heat a boiler can produce. E.g. a 15 kW boiler. This is common to all boiler systems, although some of the old ones will be in BTU’s.

Each property needs an amount of heat during one year. An average insulated house may need 20,000 kilowatt hours from a wood pellet boiler.

Wood pellets provide about 4.8 kWs of heat from 1kg. The average house may therefore need just over 4 tonnes of wood pellets a year before you take into account the efficiency of the boiler.

L – Lambda Sensor

A Lambda sensor is an electronic device that measures oxygen. It is used within wood pellet boilers to adjust the air/fuel mixture to achieve the best burn possible.

M – Cubic Meters (m3)

Wood pellets need to be stored. By volume 1 tonne takes up 1.65 m3 of space. The average house that is well insulated may need between 4 and 5 tonnes of wood pellets in a year. You can therefore work out how large your storage space needs to be taking into consideration bulk discounts and available space.

N – NOx

NOx emissions are of concern because they are associated with the increased acidity of aerosol particles, cloud water and precipitation (acid rain), causing damage to aquatic and terrestrial ecosystems, as well as being responsible for the corrosion of building materials and affecting human health. NOx can act as a fertiliser in soils but, in excess quantities, leads to eutrophication (an overabundance in nutrients leading to oxygen depletion) in many environments. Furthermore, NOx emissions are of crucial importance in the formation of photochemical smog and oxidants, especially ozone (O3), in the lower atmosphere. (Coal online)

A DECC study found that NOx levels from UK produced wood pellets ranged from 0.13 kg per mWh and were similar to both oil and gas NOx emissions.

The advantage of wood pellets is that through their compression and clean burning there is a lower transport cost and this reduces NOx emissions.

O – Organic compounds

Wood pellets are made to European standards and there are wood pellet schemes in the UK.

Wood Pellets are made from non contaminated wood ie there are no coatings such as paint. This ensures that there are no emissions from halogenated organic compounds. Wood pellets are tested in a lab for emissions. If you are unsure do check the site of your supplier or ask them about emissions testing.

If you burn wood with coatings then you will be releasing harmful emissions into the environment.

P – Pelletising

Wood pellets are made from sawdust. This may be from the milling process in which case the sawdust will be “wet” and need drying. Dry sawdust can be sourced from mature non contaminated wood waste.

The sawdust is compressed mechanically through a metal ring dye that compresses the dust into the wood pellet and produces heat. This heat causes the wood to produce lignans which acts as a natural glue binding the sawdust together.

Wood pellets are most commonly made in 6mm width. This relates to the metal ring dye and not to the length of the pellets.

Q – Quality and Net Calorific Value (Q)

Wood pellet quality is often discussed in relation to the net calorific value (q). 4.6-4.8 kW per kg is often given as the range that you may find. Fuel suppliers do compete and try to offer fuel that is of a higher net calorific value (q) such as 4.8 kW. This does affect the cost of your fuel bill and it is sensible to calculate the cost of the fuel against its energy content in order to get the best value.

R – Renewable Energy Association

All MCS accredited suppliers of wood pellet boiler installations have to sign up to the REAL Assurance scheme  for customers. This provides the customer with confidence to purchase a micro renewable device such as a wood pellet boiler from a wood pellet installer.

S – Sustainable

Are wood pellets a sustainable fuel? Clearly if everyone in the UK wanted to use them all at once and at the moment, then no. However this is not the case. Wood pellets are made from wood waste that came from sustainably managed woodland or forest.

” FSC (Forest Stewardship Council) accreditation certifies that the biomass used in wood pellets (or for other uses) came from sustainably-managed forests. FSC is not the only such accreditation scheme in the global forestry market. PEFC(Programme for the Endorsement of Forest Certification schemes) is another. You will often see the phrase “FSC or equivalent” to denote wood pellets from sustainable sources.

Just as lack of quality accreditation does not mean that a product or service lacks quality, simply that its quality has not been verified independently, so lack of FSC or equivalent accreditation does not mean that a wood pellet is from unsustainable sources, just that the sustainability of its sources has not been verified indepedently. Many smaller producers will not be able to manage the cost and bureaucracy of accreditation of one sort or another. They may be using forestry and timber-mill by-products that are the most sustainable inputs to pellet production, as they would otherwise have been wasted, but be unable to provide traceability on these by-products to sustainably- or unsustainably-managed forests. In this context, that should not matter. You should not dismiss wood pellets that are not FSC or equivalent certified, but you may want to ask more questions about their provenance.” (Forever Fuels)

T – Thermostatically controlled heat

Wood pellets are an automated fuel. This means that fuel gets fed into the burn chamber as it is needed and tops up the heat in a property as needed.

Thermostats are placed in different rooms as per gas or oil heating to regulate the heat. Thermostatic valves are also put on radiators.

This means you can have different heating zones and heat different areas of the property to different temperatures easily.

If you wanted to choose wood gasification as an option the fuel cannot be fed automatically on a small scale. Therefore wood is burnt and heats up a lot of water. This is then released automatically on demand to the house.

U – Under floor heating

Wood pellets boilers produce hot water. Using switches you can divert the hot water to where it is needed on demand. Underfloor heating is on a different heating circuit to radiators (e.g. upstairs) and needs to be controlled separately.

Underfloor heating is very popular and it is as easy to use with wood pellet heating as with gas or oil.

V – Verses

In the days where it was only gas verses oil comparisons were quite easy to show.

Wood pellet comparisons (and indeed heat pumps, solar thermal etc) have broadened the choice of consumers and in doing so have made comparisons more complex.

Do you want a comparison based on environmental performance? Cost? Ease of use? Maintenance costs?

More difficult is trying to predict the future and future price rises and availability of all fuels.

There are no guarantees. Hopefully there is some information in this A-Z that helps give you confidence that wood pellets and wood pellet boilers can be an alternative. They can be cheaper to run and installed to a higher standard. The installation can be offset with the RHI (see above), and provide effective, automated, and no hassle, heating.

W – Wood

Wood is the only ingredient of wood pellets. Although any wood can be made into pellets it is normally the softwood that is used. This is partly as it is easier to pellet as it is softer, partly it is easier to grow, and often it grows more quickly.

Many people refer to wood as “biomass”. It is  a term that is not that helpful. Biomass is simply biological material from living or recently living organisms such as trees. Therefore when “biomass” is discussed on a large scale it could mean palm oil, pine nut kernels, straw, or anything that burns.

X – “X marks the spot”

When you want to install a wood pellet boiler it takes a little thought as there are a number of variables.

  1. Where can you put the flue?
  2. Where is there space for the boiler?
  3. Where do we want the boiler and which type do we want?
  4. Can I meet all building regulations part J?
  5. Am I in a conservation area (or area of outstanding natural beauty)?
  6. Do I have a listed building?
  7. Can I meet all regulations cost effectively?

If you are having difficulty with any of these issues do not hesitate to get in contact through the form to the right or on the contact page

Y – Yearly demand for wood pellets

Most people want to compare costs based on 1 year. Unfortunately we have had a few years of volatile temperatures.

In an average year with an average house you will need 20,500 kWh’s. Last year this would have been more as 2010/11 was one of the coldest winters on record. During this time you would have used oil, gas or wood pellets to keep you warm. No fuel is better or worse at doing the job.

With gas you do pay on demand. Therefore you do not pay the summer tariffs for the majority of your gas, but the tariff when it is coldest.

Oil can be ordered and depending on the size of your hopper you can try to get through the winter, but if you get cut short then there is a wait for delivery and the price will have risen considerably.

Wood pellets are like oil in that they have to be delivered. Fortunately that is where the comparison ends. Your storage is unrestricted if you have space enough. Either to store bags or a hopper. ie you can order enough for the winter and keep some in reserve.

Pellet suppliers are keen to look after their customers and keep their own costs down. Therefore it is not uncommon for them to ring you up if they are making deliveries in the area and “top up” your supplies.

Z – Zero Carbon Home

In order to combat global warming many governments have put in place schemes that mix taxes an incentives to help individuals and organisations to reduce their carbon.

In the UK there has been a debate about what constitutes a “zero carbon” home.

When you bury down into the figures, not just on  heating, but on construction and living (e.g. food, transport etc) it is very difficult to get within a reasonable distance of this figure not just on cost grounds, but being practical as well.

A good read is “one tonne life” a project about reducing carbon emissions down to one tonne from 7.5 tonnes.

Renewable Heat Incentive Update

RHI (Renewable Heat Incentive) UPDATE – 26 OCTOBER 2011

DECC was planning to launch the Renewable Heat Incentive (RHI) for non-domestic generators on 30 September 2011. State aid approval is a necessary condition for the scheme to go ahead. As part of that process, the European Commission expressed concerns that the large biomass tariff was set too high.

The Commission has now given State Aid approval to the RHI subject to the large biomass tariff being reduced from 2.7p per KWh to 1p per KWh. Revised regulations have now been re-laid in Parliament to reflect the required amendment to the tariff for large scale biomass. We hope to open the scheme to applications by the end of November 2011, subject to Parliamentary approval.


Please note that the tariff reduction is only for “large biomass”. This is for installations above 1000 kW’s which may heat 50 or more houses e.g. a small village and larger e.g. Biomass power station

Court Hill Centre Wood Pellet Boiler Opened

The Court Hill Centre wood pellet boiler was “opened” on 21 October 2011.

Court Hill Centre

The Therminator from Solarfocus now heats all of the converted barns onsite.

This replaces the oil boilers that were inefficient and the price of oil has risen considerably.

The Renewable Heat Incentive for organisations such as this gives a choice between expensive fuel with a high carbon footprint and cheaper fuel with a low carbon footprint.

The boiler has been located in one of the barns

Oxfordshire pellet boiler

Pellet boiler and fuel store

It heats the whole of the centre which is made from 5 converted barns.  The largest of which is a bunkhouse that sleeps 60 people.

Therminator wood pellet boiler from Solarfocus

Jim Dowling technical director of  Oxfordshire Renewables has managed the project and is delighted with the results.

In the above photo you can see the boiler, to the right there is the pellet feed from the fuel store, and rising out of the boiler there is the flue.

If you are interested in installing your own wood pellet boiler, and are interested in seeing the above installation do get in touch through the contact form on the right.

Renewable Heating, Carbon Reduction and Wood Pellets

Renewable Heating – Wood Pellets have a carbon emission figure of 0.04 kg per kWh. This helps an organisation calculate carbon savings against oil or gas.

A home can work out how much carbon they are saving and understand why the Renewable Heat Incentive has been developed.

This compares against other technologies:

Heat pump with a COP ratio (see previous article) of 6:1 then the carbon emissions would be 0.53/6 = 0.09kg per kWh.

Heat pump with a COP ratio of 3:1 then the carbon emissions would be 0.53/3 = 0.18kg per kWh.

Oil is 0.265kg per kWh
Gas is 0.194 per kWh

If you are currently on Oil heating and use 20,000 kWhs of heat per year (average house) by converting to wood pellets you would save:

(0.265-0.04) kg per kWh ie 0.225kg per kWh

There are 20,000 kWhs in this example so a carbon saving of 4500 kgs per annum.

Renewable Heating, Carbon Reduction and Heat Pumps

The renewable heating market has lots of facts and figures available. One of the key political issues is “does it save carbon?” and “is the carbon reduction worthwhile?”.

What are the key things to look for?

With heat pumps there are a number of issues on calculations.

Where does electricity come from? This can be produced in any number of ways e.g. Power station and coal, Wind or Solar PV. The accepted way is to use an average. The accepted government average is 0.53 kg per kWh. This is based on Gas (0.5 kg per kWh) and Coal (possibly greater than 1kg per kWh) at the moment with a view to this being reduced to 0.43kg per kWh as a figure that can be used for projections.

What is the COP figure? The term coefficient of performance (COP) is used to describe the ratio of useful heat movement to work input. This could range from 8:1 to 2:1 for instance. The figure changes depending on the machine (Manufacturer, Air source (ASHP) or ground source (GSHP)) or the job that it asked to do (ie heating to a higher temperature will decrease the cop figure). This means that you could gain 8 units of heat (kw) for using 1 unit of electricity or 2 units of heat for 1 unit of electricity.

The heat pump does not produce carbon emissions on site, but does use electricity.

If your installation is going to use a ratio of 6:1 then the carbon emissions would be 0.53/6 = 0.09kg per kWh.

If your installation were going to use a ratio of 3:1 then the carbon emissions would be 0.53/3 = 0.18kg per kWh.

As a reference oil is 0.265kg per kWh and gas is 0.194 per kWh

Clearly as electricity is produced in a more environmental way then the carbon savings from heat pumps improve. Both examples above show some carbon savings against both gas and oil.

If you want to find out more about “green” electricity

Renewable Heat Incentive News

After much anticipation, the Renewable Heat Incentive (RHI) has been delayed at the last-minute, due to concerns from the European Commission that the large biomass tariff is set too high. The length of delay is unknown, but changing the …
http://www.logic4training.co.uk/blog/ — Mon, 03 Oct 2011 09:24:11 -0700
The Department for Energy and Climate Change (DECC) announced on Friday 30 September that the Renewable Heat Incentive (RHI) subsidy scheme will be delayed for at least two months. This announcement came just hours before the …
http://www.localenergy.org.uk/ — Mon, 03 Oct 2011 07:28:43 -0700
Very soon you will also be able to make use of a government scheme which is set to make heat pumps an even better investment. That is the renewable heat incentive, and it will work by paying you per unit of heat energy produced. It works in …
http://www.weight-watchers-uk.org.uk/ — Mon, 03 Oct 2011 07:10:16 -0700
Very soon you will also be able to make use of a government scheme which is set to make heat pumps an even better investment. That is the renewable heat incentive, and it will work by paying you per unit of heat energy produced. It works in …
http://www.ianslive.com/ — Mon, 03 Oct 2011 07:10:06 -0700
Only members of the MCS scheme are able to offer customers access to the financial benefits of the Feed in Tariff (FiT) and the Renewable Heat Incentive (RHI). Furthermore, installers who are members of REAL Assurance membership …
http://www.renuvo.co.uk/ — Mon, 03 Oct 2011 06:19:42 -0700
http://t.co/xZjS6aPz; NEWS: Renewable Heat Incentive withdrawn by government hours before launch via @guardian #energy · http://t.co/ENcuAX8l; UK cod collapse due to overfishing and political failure, says fisheries expert via @guardian …
http://www.life-size-media.com/blog/ — Mon, 03 Oct 2011 06:05:21 -0700
The UK’s Feed in Tariff and Renewable Heat Incentive, has triggered a substantial increase in demand for Solar Photovoltaic (PV) and Biomass Heating installations alongside our Gas Maintenance and Installation activities. As a result …
http://www.renuvo.co.uk/ — Mon, 03 Oct 2011 05:33:35 -0700
EU state aid rules delay Renewable Heat Incentive launch. 03.10.11 at 11:53 AM. Industry furious as launch of flagship scheme is put back by at least a month. The government’s flagship scheme for encouraging businesses to install low …
http://www.worldcarbon.co.uk/ — Mon, 03 Oct 2011 03:53:17 -0700

Renewable Heat Incentive for Businesses

The Renewable Heat Incentive for businesses is being offered to businesses to help them cut their fuel bills and gain a return on investing in renewable technology.

Biomass solutions include wood pellet boilers, wood gasification boilers, and wood chip boilers.

The scheme was to be introduced on the 30th September but it has been delayed until November 2011.

”We are fully committed to introducing the Renewable Heat Incentive. However, we understand that the European Commission state aid approval for the RHI will be subject to a reduction in the large biomass tariff. We expect to receive written confirmation of this very shortly. This means we now need to change the regulations before the scheme can open to applications. We understand this is frustrating for industry who are already gearing up for the RHI however we hope to get this sorted out soon and open the scheme before the end of November.” DECC 29th September

For further information please see or here