How Wood Energy (and Biomass Boilers) Work

Woodburners
A wood burner is typically made of cast iron, with a single combustion chamber. The fire has to be started manually and wood loaded in manually. There will be at least one controllable air intake, which affects the rate of the burn. The stove will be connected to a flue. The grate will need emptying of ash from time to time, and the flue will need to be cleaned by a sweep two or three times a year.

Automatic feed boilers, like pellet boilers, chip boilers and log boilers, consist of a number of components; a main hopper and mini hopper for the fuel, the feeder, the combustion chamber, a hot water buffer cylinder, an ignition system, a fan, and various control devices. They fall into different categories according to where the fuel is fed into (e.g. top feed, under feed or horizontal feed).

Fuel
Pellets are the most efficient form of wood fuel, followed by wood chips, but logs can be the cheapest if you have a good local supply. Pellets are made from waste wood, and logs are often produced as a result of forestry work or tree work by tree surgeons.

Frequently Asked Questions About Wood Energy (or Biomass)

We recommend Stoves Online for a comprehensive list of frequently asked questions: www.stovesonline.co.uk/stove_help_and_advice.html.

Before you take the next step:

You need to decide how far you want to go – a complete wood-fuelled heating system or a stove for heating one room, or something in-between.

You will also need to look at where the stove could be sited. A flue will need to exit the roof about 1m above the highest point.

When you have decided what you want your stove to do and how large it should be, then you can start having a look at what is available.

1. Check with your local council that you are not in a smoke free zone, as this will constrain your choice of stove or boiler.
2. Think about whether you want just a room heater, or you want something that could potentially replace your oil or gas for heating some or all of your rooms and your domestic hot water. Also think about whether you need an automated system or are happy to light it and feed wood into it manually.
3. Consider where you want the stove located, as this will affect the cost and effectiveness of the installation. E.g. if you are able to reuse an existing chimney, then the flue costs will be less, but you will be losing more heat if the chimney is on an outside wall.
4. Discuss the options you are considering with a reputable and experienced chimney sweep. Generally, the straighter the flue the easier it will be to clean.
5. This is optional, as a supplier can calculate this for you, but you can work out how powerful a stove you need. This is measured in kilowatt hours (kWh). There is handy calculator at Stoves to You : www.stovestoyou.co.uk/stoves/calculating_size.
6. Visit a number of local showrooms, and research online, to see what kind stoves are available. A number of stoves are now made in the UK including Aarrow, Hunter, Villager, Woodwarm and Yeoman in Devon, Hotpod in Cornwall, and Charnwood on the Isle of Wight.
7. If you are considering a stove as part of your heating system, or would like to buy a stove with an integral boiler with a view to sometime in future linking it into your heating system, then select local suppliers to give you quotes who have experience of setting up systems with multiple heat sources (e.g. gas boiler, woodburning stove, solar thermal panels). You can find these using the Microgeneration Certification Scheme website at www.microgenerationcertification.org.
8. Always get at least 3 quotes.

Costs & Grants for Wood Energy

Average Costs

As of January 2012, the average cost of installer a standalone woodburning stove was around £1,500, including installing a flue. Installing one that heats hot water for domestic use and central heating will add further costs, e.g. additional pipework, a twin-coil hot water cylinder, extra controls, and the cost is more likely to be in the range of £6,500 – £12,000.

A boiler, pellet, chip or wood, will cost from £5,000 – £12,000 for an average house.

The Renewable Heat Incentive (RHI)

The Renewable Heat Incentive is a new Government-backed measure being introduced to make it worth your while to produce renewable heat. You earn a fixed income for every kilowatt hour of heat you produce. This is likely to be used in your own property, but if you are lucky enough to be connected to a heat network you might be able to get an additional payment for ‘exporting’ surplus heat.

The launch of the Renewable Heat Incentive (RHI) has now been further delayed. However, the tariffs have been published.

Eligible applicants will receive:

• at least 19.2 p/kWh for solar thermal
• 18.8p/kWh for ground source heat pumps
• 12.2p/kWh for biomass boilers
• 7.3p/kWh for air source heat pumps

Renewable Heat Premium Payment Scheme

Meanwhile, until the RHI is available, the Renewable Heat Premium Payment scheme can assist with some of the upfront costs. If you install the following technologies after 20th May 2013, and have had a Green Deal Assessment carried out, then you could be eligible to receive the following voucher amounts:

• £2,300 towards Ground or Water Source Heat Pump
• £2,000 towards a biomass boiler
• £1,300 towards an Air Source Heat Pump if used with a water-based central heating system
• £600 towards solar thermal hot water

(If the install was before 20th May, the RHPP is still available but the voucher amounts are smaller.)

The Renewable Heat Premium Payment scheme is expected to close on 31st March 2014.

Benefits & Rewards of Wood Energy

All of the wood-burning options, apart from open fires, will:

• Save money
• Reduce CO2 emissions
• Provide more energy independence

However, with wood burning stoves, there are some other key benefits:

• They look good
• They feel cosy
• They connect with that primitive need to feel warm and safe
• They can add value to a property

The key advantage of pellet boilers and wood chip boilers are:

• Convenience – no supervision of the equipment is required, although the pellet-burner will need cleaning out about once a month.
• High energy density of the fuel
• Consistency of the fuel
• Both pellets and chip are more efficient for transport and storage, with pellets having the edge.
• Pellets are typically made from waste wood products.

The Renewable Heat Incentive (RHI)

The Renewable Heat Incentive is a new Government-backed measure being introduced to make it worth your while to produce renewable heat. You earn a fixed income for every kilowatt hour of heat you produce. This is likely to be used in your own property, but if you are lucky enough to be connected to a heat network you might be able to get an additional payment for ‘exporting’ surplus heat.

The launch of the Renewable Heat Incentive (RHI) has now been further delayed. However, the tariffs have been published.

Eligible applicants will receive:

• at least 19.2 p/kWh for solar thermal
• 18.8p/kWh for ground source heat pumps
• 12.2p/kWh for biomass boilers
• 7.3p/kWh for air source heat pumps

Good Energy’s Renewable Heat Incentive

Green energy suppliers Good Energy have their own Renewable Heat Incentive called HotROCs which rewards customers who are generating heat or hot water from renewable sources.