A biomass boiler, unlike a standard boiler such as gas or oil, burns plant products in pellet or chip form. Because we are dealing with solids as fuel, it will produce ash and clinker as a waste product. For the smooth operation of a biomass boiler, it, therefore, needs a thorough cleaning and regular servicing to prevent any problems with fuel delivery or waste removal.
The regular biomass boiler has a fuel compartment or hopper, that holds the unburnt fuel. The fuel will either be fed to the boiler automatically or will require manual operation depending on the type and cost of your boiler. As the fuel burns, it produces ash that must be removed as it accumulates. Depending on the efficiency and size of your wood burning boiler this could be as frequent as once a week or as infrequent as once a year.
Table of Contents
- 1 Why are domestic biomass boilers so attractive?
- 2 What types of fuel are used?
- 3 Renewable Heating Incentive (RHI) Scheme
- 4 What servicing and maintenance tasks should be done?
- 5 How much will servicing a biomass boiler cost?
- 6 Biomass Boiler Costs: Installation & Maintenance
- 7 Which boilers are eligible for the RHI?
- 8 To finish
Why are domestic biomass boilers so attractive?
Even though a biomass boiler burns fuel it is, in fact, a carbon-neutral heating system. This is because when the wood burns it gives off the same amount of carbon dioxide as it absorbed when it was growing, effectively cancelling out the two sides of the equation. They do not burn coal which spent millions of years absorbing the carbon dioxide and then dumping that amount into our atmosphere in a few hours. If it is working efficiently and as it is designed, a biomass boiler is capable of energy efficiencies (about 90%) comparable to a high efficiency gas or oil boiler.
What types of fuel are used?
There are three basic types of fuel. Let’s start with the least efficient and finish with the best:
- Some biomass boilers use logs as a fuel, but these are actually far less efficient than the other types. Logs tend to hold high levels of moisture (25% to 30%) and need to be dried out for a long time before use. Damp and unseasoned logs will produce a lot of smoke and tar. They will, therefore, need space for storage both for wood already seasoned and for wood yet to be seasoned. Logs cannot be fed automatically into a boiler via a hopper so will have to be loaded manually.
- These are logs and other wood products that have been fed through a wood chipping machine. They tend to have the same moisture content as logs so will produce smoke and tar. Chips are not as compressed as pellets so will take up more room in storage and transportation, but they are cheaper and simpler to produce.
- Pellets are made from many different materials, the most common being wood byproducts such as sawdust and wood shavings. They have a consistently low moisture content of between 5% to 10%, and they are a consistent and uniform size. This means that they are easily automatically fed into the boiler’s combustion chamber from a hopper. Other common biomass pellets are made from waste products such as dried animal waste (manure), dried human waste (unused food products and items destined for landfill), plant residue (straw, grass clippings, prunings). All these substances, if not used in a domestic pellet boiler, could cause disease, contamination of water courses, or end up in a landfill. Some plants, such as hemp, corn and soya beans, are grown partially for energy and food products. Once the edibles or useful parts have been harvested, the remainder is processed into combustible pellets for domestic biomass heating systems.
Biomass isn’t just about solid pellets made from plants and manure, there are other types too. Biomass can be converted into biogas such as methane or into a liquid such as ethanol and biodiesel. All these types of biofuel can be burned to produce energy.
- Biogas is formed from the decomposition of paper, food scraps and garden waste as well as the digestion of sewage and animal manure.
- Biofuel ethanol is made from the fermentation of corn and sugar cane.
- Biodiesel is made from vegetable oils (secondhand and new) and animal fats.
The liquid and gas biofuels are very rarely used in a domestic biomass boiler. The gases are more likely to be used in a commercial plant or in a biomass power station, while the liquids can be used in vehicles and as heating oil.
Renewable Heating Incentive (RHI) Scheme
Apart from the environmental benefits that a biomass boiler system will give to all of us, there are benefits that will affect the householder in the short term. The Renewable Heat Incentive (RHI) is a scheme set up by the UK government to encourage householders to use renewable fuels. Biomass boilers have high installation costs so the incentive is to buy a boiler accredited by the Microgeneration Certification Scheme (MCS) and have the boiler installed and serviced by an MCS engineer. In return, the UK government will pay the householder a fixed amount for every kilowatt-hour of heating produced. At the time of writing, this is 6.88p per kWh. The current and historical tariffs can be checked on the Ofgem website. The payments to the consumer will be paid quarterly for seven years.
What servicing and maintenance tasks should be done?
These are divided into those tasks that can be done by the householder and those that must be done by the MCS accredited engineer.
- The householder. Because the wood burning furnace uses solids as a fuel, there will be solid waste products left over after combustion. Keep the boiler serviced at the required intervals and as well as removing the ash and clinker, keep an eye on the quality of the ash deposit. If there are signs of unburnt fuel within the ash, that is a sign of inefficient burning. Similarly, large soot and clinker deposits within the combustion chamber, as well as excessive black smoke production, are all a sign that a service is due. Don’t forget to have the chimney flue cleaned by a registered chimney sweep who will issue you with a certificate. Clean the fuel store at least once a year. Any of these irregularities may prevent the boiler from working efficiently and will also cause increased production of carbon monoxide. It is also the householder’s responsibility to ensure there is a carbon monoxide detector installed in the same room as the boiler. There will be a control panel fitted to the boiler that indicates the temperature of the flue gases when leaving the combustion chamber. If the temperature is too high then it is a sign that ash build up is preventing the heat exchange from working properly. It can also indicate variations in the oxygen content indicating incomplete combustion and the production of carbon monoxide. Don’t even consider using poor quality fuel. For good boiler efficiency, you need to maintain a good quality fuel and monitor fuel consumption.
- MCS accredited engineer. Regular servicing as well as dealing with combustion chamber problems must be done by an MCS accredited engineer. If you are in receipt of the RHI then all work on the boiler must be done according to the manufacturer’s instructions and by an MCS engineer. A typical residential biomass boiler service may consist of
- A general inspection of all working parts and the overall condition of the boiler.
- Cleaning and clearing of any obstructions in the air intake or waste gas exit ports.
- Cleaning and inspection of the combustion chamber.
- Cleaning and inspection of the heat exchanger.
- Check, grease or replace if necessary all seals and bearings.
- Replace all worn components of the boiler.
- Inspect and test all safety equipment and instrumentation.
- Inspect fuel hopper and any associated equipment.
- Analyse the flue gas composition and check the efficiency of combustion.
Servicing a biomass boiler is not a quick job and may take anything from 2 or 3 hours up to half a day.
How much will servicing a biomass boiler cost?
As you can see, there is a lot of work involved in a service and if some parts need replacing then you will have to pay for those too. If you need spare parts for a biomass boiler, costs can vary depending on the brand of boiler, the size of it and which parts are needed. For labour only, an indicative price for servicing will be about £200 for a small biomass wood boiler, while a larger model could cost around £500. Some biomass boiler installers realise that the cost of servicing and spare parts can work out very expensive if the householder is invoiced after each service. To encourage consumers to have their boilers serviced, many companies offer a monthly payment scheme where for a regular payment, they will keep your boiler in tip-top condition and include the cost of spare parts as well. Ask your local installer if they have a scheme like this and when they tell you the price, ask if it includes VAT as many contractors forget that the ordinary person wants to know how much it is costing them altogether.
Biomass Boiler Costs: Installation & Maintenance
In order to see if installing one of these boilers is economically worthwhile, you need to know approximately how much they will cost to install and the typical running costs involved.
On average it costs about £10,000 to £15,000 to install a biomass heating system in a 4 bedroom detached house. The RHI usually will pay back between £1,500 and £3,000 per year over a repayment period of 7 years.
The major ongoing running cost will be the purchase of biomass fuel. Typical costs of fuel include £150 per tonne for good quality wood pellets while for wood chips the cost will be around £80 per tonne. A typical domestic boiler, depending on size, building size and climate, will use in the region of 10 to 15 tonnes per year. If you are tempted to use cheaper, poorer quality fuel remember that quality pellets will create less ash and smoke and produce more heat resulting in better energy efficiency and a reduction in boiler damage.
Regular maintenance is another running cost that must not be skimped. As well as the regular maintenance regime already mentioned it is important that the flue, thermostat and motor should be cleaned and maintained. Regular maintenance will always reduce higher expenditure on spare parts.
Which boilers are eligible for the RHI?
In order to be eligible for the RHI, your boiler must comply with a few standards and requirements such as:
- It must burn biomass only or if the output is less than 45kWth it must be MCS accredited.
- Must be installed after 15 July 2009.
- The property must be in England, Wales or Scotland.
- You must own the property.
- The boiler and associated equipment must be new.
- It must be installed by an MCS engineer and have an MCS installation certificate.
- The installation must receive an Energy Performance certificate.
- The installer must provide a Green Deal Advice Report.
If your boiler and equipment comply you must submit an application during the first year after installation after which, if approved, payments will be sent quarterly.
Domestic biomass boiler systems can be very useful as a simple way to heat a house and can provide many advantages over conventional gas and oil central heating systems.
If we install a biomass boiler into our homes we will be assisting the planet by using a renewable energy source that unlike other combustion heating systems uses a fuel that is carbon neutral, is clean while being stored, is not dangerous when stored or if there is a leak and it comes into contact with the environment, and diverts waste products from landfill sites.
As long as a biomass boiler and its associated equipment are kept clean and are serviced regularly there is no reason why the energy efficiency cannot favourably compare to current high-end gas and oil boiler systems.