Frequently asked questions

A biomass heating system can either be a boiler or stove designed to burn solid fuels classed as biomass. There is a wide range of boilers and stoves available in the market place each capable of burning a variety of fuel sources such as wood chips, wood pellets or logs. Even agricultural waste materials such as straw and grain husks, rice and sawdust can be used as fuel, although these need to be designed to burn specific materials.

All biomass boilers can be connected to most existing central heating systems, while biomass stoves must have a back boiler to contribute to the heating systems. However, certain checks must be taken first before installation, as many biomass boilers operate at a higher temperature and pressure, than oil and gas boilers. Some operate at temperatures above 100C with additional equipment such as a heat exchanger to manage the new higher input temperatures.

This very much depends on the design of the biomass boiler and the system that it integrates into. A carefully designed system can be as responsive as a fossil fuel system, depending on the size of the buffer tank and the fuel type used. A large buffer tank, can be charged by a biomass boiler in advance allowing the system to draw heat when required. For systems with smaller tanks, the biomass boiler will be slower to respond to changes in the heat demand. Typically biomass boilers regulate their output though a combination of control loops used to control the fuel feed rate, air fans and a Lambda sensor as a feedback sensor to monitor oxygen levels in waste gasses.

A properly designed and installed biomass heating system will be as reliable as a fossil fuelled boiler and should not need a back up for domestic or commercial projects. However, as a biomass boiler is rarely sized to meet the peak load, the back-up boiler usually acts as a peak-lopping boiler as well. Hence, it is usual for back-up boilers to be sized to meet the peak load.

Biomass boilers operate at their highest efficiency, and are most reliable, when operating continuously, rather than modulating to fluctuations in demand. They generate a far higher temperature output than heat pumps and as such offer both advantages and disadvantages in their use, compared to a range of heating technologies.

Their higher outputs are suitable for buildings with greater heating loads to maintain a comfortable room temperatures. Typically, the historical building stock within Britain, ranging from Victorian farm houses to Georgian town houses are poorly insulated and suffer from damp issues when poorly heated. Although insulating these properties should be undertaken to improve their efficiency, this can be expensive when done with the care and attention required to prevent other problems from occurring. By replacing existing fuel systems with a biomass boiler you can reduce the running costs without compromising on the comfort.

Projects that require continuous heat loads such as schools, hospitals, swimming pools, district heating and nursing homes are suitable for the large constant output that biomass heating generates. In addition, a buffer hot water storage tank can modulate outputs to suit most projects.

Like fossil fueled heating systems, biomass heating boilers and stoves require annual service by a HETAS registered technician. In addition to the annual service, biomass boilers require frequent checks and maintenance. Weekly inspections should be carried out to check the feed mechanism, visual assessment of the combustion chamber, check the lubrication of bearings and to empty the ash tray. A monthly cleaning routine of the flue tubes is also recommended.

Typically, the hot water demand of a properly sized biomass heating system equates to only 5-10% of the boiler output, which is less than the minimum boilers are able to achieve. A correctly sized buffer tank can store the heat, allowing the boiler to operate for a short time to charge the vessel, removing the need to have your heating system continuously on during the summer. Alternatively, we would recommend installing solar thermal panels which compliment biomass systems. During the hot summer months, while the central heating system is not usually operational, solar hot water panels are usually able to generate enough hot water to satisfy domestic demand.

In any biomass system you have the fuel storage, hot water storage buffer tank, boiler unit and accessories to deal with waste. Fuel storage requirements will vary depending on the type of fuel being used. Pellet based systems can require a silo, where pellets are blown into a the silo and a mechanism draws the the fuel to the boiler. A buffer tank can vary in size depending on the size of your property, the number of inhabitants (hot water demand), the size of your boiler and the frequency at which you would wish to run your boiler. This is an important feature to your system which can manage the peaks and troughs in the supply and demand of heat while maximizing the efficiency of your system. To deal with the waste, a flue would be used to allow waste gases to escape. This may require filters to treat and clean the flue gasses.

Typically, the majority of biomass boilers and stoves can operate for up to a week without any manual intervention. The controls can be configured for time switch or optimum start/stop, fuel feed, de-ashing and flue cleaning. Smaller boilers, or systems with limited fuel storage may have limited automation.

Depending on the biomass boiler’s specification’s almost all biomass materials can be burned and used as fuel. However, most systems are designed to operate on seasoned logs, wood chips or pellets. In batch fed boilers, supplementary materials such as straw, masicanthus, sawdust, wood off cuts, and waste wood can be used. These materials may be subject to the Waste Incineration Directive which prohibits the burning of materials contaminated by heavy metals, (such as lead based paint). When burning non standard fuels there may be potential problems of slag formation, combustion control and emissions.

Wood pellets are a manufactured biomass fuel, made from sawdust and other waste products of sawmills and wood based manufacturing processes. This waste material is compacted into 6-8mm pellets. One kg of dry wood pellets has the calorific value of 4.8kwh. The comparison to heating oil, 2kg of wood pellets has the same calorific value of 1L of oil. The cost of wood pellets compared to heating oil comes down to approximately 35p for 2kg (£150-£230 per tonne) of pellets compared to 60p for 1L of heating oil. The cost of wood pellets depends on transportation costs and your nearest supplier. Good quality wood pellets should have a minimum moisture content of 10-12% to burn efficiently, they should be clean, flow freely and be mechanically robust. (Prices used as of 2012).

Wood pellets boilers and room heaters can be fully automated, turning themselves on and off: adjusting to pre set heating demands, much the same as gas and oil boilers. Pellets have a lower moisture content compared to other biomass fuels and as such have a more efficient burn.

Wood chip fuels are processed waste wood through a chipping machine. This fuel can either be bought, or made by yourself. Wood chip can be even more cost effective than wood pellets due to their material content and if you make your own. Typically the calorific value of one kg of wood chips is around 3.5Wh, depending on moisture content.

Both systems require the fuel to flow into the boiler. Due to their uniformity pellets are relatively free flowing, however, wood chip tends to be less consistent and would require an agitator mechanism to keep wood chips flowing. Without the agitator arm, the chips could solidify into a solid mass blocking the feed into the boiler.

Miscanthus is a grass that grows through the UK, it has been developed into a biomass energy crop. It has considerable potential in a wide range of biomass applications with a burn time of 3.6 hours per Kilogram.

Any owner of a biomass heating system should invest in a moisture meter. This simple tool will enable you to distinguish between dry and well seasoned fuels which will burn efficiently and lower quality fuels. This tool will also enable you to verify the quality of fuels being delivered is equal to that specified during ordering. Other than moisture content, pellet fuel sources should have few problems with sourcing quality fuels from reputable suppliers. Operators of wood chip boilers, however, need to be aware of the many fuel quality issues which can arise with the use of wood chips. Since wood chip undergoes fewer manufacturing processes and can be sourced from a wider range of ‘waste’ materials, the quality can vary. Wood chip fuels have the potential for contaminants particularly sand, which causes slag to form, and foreign objects, such as stones and lumps of metal, which can jam or break auger feed mechanisms. Owners of any biomass equipment must ensure that the fuel being used matches that of the capability of the boiler and the manufactures guidelines.

Biomass fuels can vary in cost depending on your local supply network. The cost of transportation, the development of a pellet supply chain and your proximity to rural areas can all have an impact and of course if you are able to source your own wood logs from your own property your fuel costs will be very low. Typically, wood logs, chips and pellets cost consistently less than heating oil and in 2009 were marginally cheaper than mains gas.

While woodchips are always cheaper than wood pellets on a per kWh basis, they vary considerably in the quality, including the moisture content which can erode any benefit in price. A local source will always have lower costs, typical transportation costs add £10 to every tonne of fuel. When your fuel has a higher density of calorific burn, the transportation has a lower impact. Wood chip prices vary considerably, however pellets can come to between £150 - £230 a tonne. (Prices as of 2012).

The amount of fuel you need will depend on the heating demands you require (temperatures, volume and length of time it is operated) and the consequence size of your system. In addition to the system requirements, the calorific value of the fuel and density will effect the quantity of fuel you required. For example a 10kW boiler operating at 90% efficiency for 10 hours a day for 7 days would require: (7days x 10hr x 10kw)/0.9 = 777kwh (4.8kwh per 1 kg of pellets) would equate to 162kg of pellets, costing less than £30 a week.

Fuel can be supplied in bags individually or on pallets, or as logs in a jumbo bag. For large scale delivery (lower costs), woodchips can be tipped into a prebuilt silo or storage areas. The same can be done for wood pellets, which can sometimes also be blown into your silo by the delivery vehicle.

All fuel should be stored in a dry environment. For domestic sized biomass heating systems, the fuel is usually manually handled into a boiler or small hopper feed so pellets and wood chip can be stored in a dry shed, garage or out-building. For automatically fed systems with an attached silo to the boiler house the delivery vehicle can tip Most automatically fed boilers require a fuel silo attached to the boiler house. This silo then requires access for the delivery vehicle to tip fuel into the silo or for pellets to be blown in using a hose, up to a maximum of 20m.

All installations of biomass heating systems in existing properties would require a building warrant. However, it may not require planning permission for the installation of the biomass boiler. This depends on whether a boiler house/fuel storage is required and the construction of a flue. Other considerations may include the dwelling or location such as listed, preservation orders on the property and smoke control areas.

Yes, if the boiler is on the exempt appliance list. If the boiler is not listed, Local authorities may be persuaded to allow the use of such a boiler as long as they are satisfied that any emissions would not be considered a nuisance nor be prejudicial to health.

The simple answer is yes. There is an EU directive (Directive on Waste Incineration,) outlining what materials can and can’t be burned. Typically materials which are contaminated should not be burnt. Such contaminates include heavy metals (commonly found in lead based paint, demolition waste) and halogenated organic compounds such as pesticides, sheep dip and other materials containing iodides, bromides or chlorides. The directive permits the burning of waste wood as thermal recycling, where the heat is used beneficially.

This is very much dependent on the fuel which you burn. Fuel which contains a high moisture content will produce black smoke. Typically most well designed and operated biomass heating systems, fed with quality fuel, should not produce any smoke.

Biomass heating systems will produce CO2 as a bi-product of combustion, in addition some oxides of nitrogen, particularly nitrogen dioxide is produced, but no sulphur oxides are emitted. The levels of nitrogen oxide produced is lower than oil boilers and is comparable to that of gas boilers depending on the temperature of the biomass boiler.

Small quantities of ash can be disposed of in landfill sites, however the high levels of potash, which is ideal for composts, can be used by horticulturalists in the garden or by farmers as a top dressing.

This very much depends on several factors but it’s probably best to assess it against what fuel is being replaced, i.e. gas, electric or oil, and the cost of those fuels against the cost of the biomass fuel. Typically the cost of fossil fuel fluctuates depending on global fuel prices. Although these rise and fall with economic activity, due to dwindling global supply and rising demand, the general trend is for the prices to increase. In addition, the cost of biomass fuel varies depending on local supplies of fuel. Clearly for someone with a plentiful supply of free biomass fuel from their own property, the running costs will be extremely low.

Generally, biomass fuel prices are comparably lower than that of fossil fuels making the payback period in the region of 8 years or less. This figure depends on the current grants scheme and the upfront costs of the capital expenditure.