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Biomass heating with a pellet stove or pellet boiler

Pellet stoves are incredibly efficient and use sustainable ‘biomass’ fuel. Much more technically advanced than wood burners, they are often self-lighting, thermostatically controlled, and can even produce hot water for your home. Some pellet stoves even have computerised controls keeping the burn as efficient as possible.

pellets picture, image

Biofuel pellets are a sustainable fuel resource

Stoves that burn scrap wood (rather than deliberately sourced firewood) have been around for years, but the first true ‘pellet’ stoves appeared in the 1970s during the oil crisis. In the last few years biomass pellet fuels become have popular as they use sustainable materials such as sawdust, straw and grains as fuel. Pellets are fed into the stove from a hopper, creating a continuous burn that requires very little attention.

How do they work?

Pellet stoves work under pressure. The fire is controlled using an internal blower, and because of this they need special double-walled venting, unlike conventional wood stoves. An advantage of many pellet stoves is that they can be vented horizontally, rather than vertically, and so require no ‘chimney’ in the accepted sense. Instead, they can be vented out through a wall, below the roof line, in the same way as a gas or oil-fired boiler. Some stoves require an externally-mounted air intake. This means the air required for the burn is not taken from the room in which the stove sits, but from outside the house. This allows far more efficient heating than most wood stoves and all open fires.

pellet stove, image

Pellet stoves usually have a second blower which circulates air from the room around the burner. This means they can function as a blower heater, warming up the room very quickly. When properly maintained, pellet stoves create no creosote residues within the flue, although for safety reasons it should still be swept. Stove manufacturers give advice about the best types of pellet to use with their appliances, as they vary considerably. Using the right grade of pellets affects the amount of maintenance time and effort required from the owner.

Government incentives

The UK government currently provides an incentive of £950 for domestic wood pellet stoves, known as a Renewable Heat Premium Payment (RHPP). This is being replaced in October 2012 by the Renewable Heat Incentive (RHI) scheme, which is already in force for the industrial, commercial and public sectors, as well as not-for-profit organisations and community schemes. The RHI is a little more complicated and will involve an approved, calibrated meter being installed on the stove by a qualified engineer, and pays out in two tiers depending on the amount of heat generated by the stove. All domestic installations commissioned on or after 15h July 2009 can apply for support. You can find out more about RHPPs and the RHI scheme on the Department of Energy and Climate Change website.

Pellet stoves – advantages:

Pellet fuel is carbon-neutral: the carbon released is simply what was absorbed during the life of the plant from which the pellets were made. If the fuel is suitably dry, pellet stoves are incredibly efficient at converting it into to heat (up to 95%) and the combustion process leaves very little residue. Many stoves are self-lighting, programmable and thermostatically controlled, so they can be set to turn on in advance. Some stoves have hoppers large enough to last several days between fills.

Pellet stoves – disadvantages

Using a pellet stove is accompanied by the constant sound of the blower(s) and the pellet delivery system, so don’t expect it to be silent – especially when it’s being run at full power. Because all these elements require electricity, pellet stoves don’t work during a power cut. Service maintenance should be carried out by qualified electrical engineers, and the flue still needs to be swept.

Things to check

Before you decide to install a pellet stove, check for local fuel sources and quality. Depending on where you live, your fuel may be imported; if so, the carbon footprint of your stove is increased substantially. Work out the running costs using ‘refined’ pellets, which have been cleaned to avoid releasing a cloud of dust when you refill the hopper. Pellet stoves are intended to burn fuel with a specific moisture content of below 6%, so damp fuel is bad news. This means that they should be supplied in bags rather than loose in the UK, or they are likely to absorb moisture from our damp air.

A small heating stove rated at 2.5kW will cost around £2000, while a larger one rated at 11kW will be around £3300. Boiler stoves, which tend to be larger and more complicated, may cost up to £4050 for a 21kW model. Stove installation costs are additional. Fuel pellets cost more in small quantities, but if the load is too big to carry yourself you’ll also pay a delivery charge. A small pellet stove may use around a kilo of pellets per hour, while a larger heating model may use twice as much. Boiler models use more.

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10 Responses to “Biomass heating with a pellet stove or pellet boiler”

  1. Paul Riding says:

    FYI. Wood Pellet STOVES are NOT supported by either the RHI or the Renewable Premium Payment. Please see Energy Savings Trust page:
    http://www.energysavingtrust.org.uk/Generate-your-own-energy/Wood-fuelled-heating about 3/4 of the way down.

    • Mark Gatter says:

      Yes, you’re correct – stoves are not currently supported, and although the anticipated RHI details haven’t yet been published they’re not expected to support stoves. Given the current government support of things solar, any subsidy is probably a case of get it while you can…because the rug could be pulled tomorrow from beneath what is promised today.

  2. Great website and ace post.
    There are many industrial and commercial properties making great use of a wood pellet boiler – keep spreading the word

  3. Between disadvantage there is the fact that a pellet boiler needs weekly cleaning from ashes to be performed when the boiler is switched off and cold

    • Mark Gatter says:

      Actually this only applies to some boilers. For the ones I’m using (from Okefen) the ash can be emptied during operation, and it only needs to be done every 6 weeks or so.

  4. Great article. When people know how a biomass boilers works and how efficient they can be, they are more inclined to start using one!

  5. If the fuel is suitably dry, pellet stoves are incredibly efficient at converting it into to heat (up to 95%). So it’s very important to storage your pellet in dry!!

  6. “If the fuel is suitably dry” – can it be here in UK?

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