Biomass Stoves

What do we mean by Biomass?

Biomass is material that is made from biological products, such as wood and plants that can be used to produce energy when burned. There are a number of different types of biomass fuels, however, the most popular types of biomass for domestic space heating and hot water purposes are logs, wood chips or wood pellets.

Biomass pellets are made from low-grade by-products of the wood processing industry such as dry sawdust and shavings, produced in large quantities. The material is compressed under high pressure and extruded through a mould to form pellets. The heat they produce is comparable to domestic heating oil, however, they are approximately 40%* cheaper and require less storage space than lower density fuels such as wood chips.

What are Biomass Stoves?

Biomass stoves can offer a very low cost supplemental (or in some cases, primary) heating source for the home. They may look like traditional wood burners, but the similarities end there. The two main types of system in the UK are:

Wood-Burning Stove
A modern wood-burning stove can burn a number of different types of wood products, from woodchips of varying sizes through to logs. They are set, lit, and stoked by hand like a traditional wood burner. However, they have the benefit of being far more efficient, and so require less amounts of wood than their predecessors. When they burn, they release less smoke during operation and produce dramatically less ash.

Pellet Stove
Pellet stoves are very similar to wood burning stoves, although instead of burning wood, they burn small biomass pellets. They are more sophisticated combustion appliances that have the advantage of being more user-friendly than a wood burning stove. Rather than having to set and light a fire on a daily basis, with a pellet stove pellets are automatically fed into the stove (from a hopper that generally holds about two to three days worth). The fire can also be lit electrically, and with some models this can actually be requested by text message remotely, so you can get your room warm for when you arrive.

Why is biomass considered a renewable low carbon fuel?

The primary source of energy contained within all biomass fuels is energy from the sun that is captured and stored via the process of photosynthesis. This energy can be released and used (e.g. by combustion). When this occurs, CO2 is released. However, the CO2 released is largely offset by that which was absorbed in the original growth of the biomass, or which will be captured in the growth of new biomass to replace the biomass being used (as illustrated above). Consequently biomass combustion is considered to be a low carbon technology if the material is derived from sustainable sources.

How does a Pellet Stove work?

Pellet stoves utilise electronically controlled combustion, blowers, and highly effective heat exchangers to provide reliable, efficient heating. You pour the pellets into a holding bin or hopper, which is located either at the top or bottom of the unit.

Most stoves have an electrically operated spiral conveyor (auger) that delivers pellets from the hopper to the combustion chamber. The auger’s movement is operated by a control that is set manually or, for some stoves, by an optional wall-mounted thermostat. A fire’s size depends on the rate of feed. The pellets are fed to a fire pot or burner ring in the combustion chamber. Combustion air is blown into the chamber to encourage a super-heated flame. You must light some pellet stoves; others are self-lighting.

Room air is drawn in by a fan and blown across the heat exchanger, which is heated to about 250C, and the warmed air is returned to the room. The sides and rear of many stoves are specially shielded in order to a create convection flow of heated air. Unlike the majority of wood stoves, most pellet stoves rely on convective heat, rather than radiant heat. As a result, most pellet stoves don’t get too hot to touch which can be an important consideration for families with small children. Although some models deliver heat by a combination of convection and direct heating, where the glass front delivers the heat directly into the room.

Residual combustion gases are vented outside, normally through a 3-inch flue that exits out the unit’s back or top. Though most pellet stoves don’t require a conventional chimney, saving you from considerable expense and design inflexibility, most types draw better if the flue goes out through the wall and turns upward. For safety and soot control, it’s wise to extend the vertical section past the eaves.

Biomass stoves produce heat which is transferred to air and used for space heating and in the case of back boiler models, water heating (not shown). 1. Pellet Hopper, 2. Spiral Conveyor, 3. Combustion Chamber, 4. Fan, 5. Heated air, 6. Glass front, 7. Flue, 8. Ashtray.

What can it be used for?

A large variety of biomass stoves are available in a number of styles, both traditional and modern, for freestanding and also fireplace inserts. The freestanding stoves can generally be placed against most outside walls and a flue created. The fireplace inserts allow you to use an existing fireplace as a location for the stove to sit in. Biomass stoves can be used in the following applications:

Space Heating
The most common use of a biomass stove is to provide space heating for a single room. and they generally have 5-7 kW output that is sufficient for this purpose. They can sometimes be positioned to provide supplemental heating for adjoining rooms.

Space Heating & Water Heating
It is also possible for some models to be fitted with a back boiler that can provide water heating when the stove is lit. These tend to have higher outputs and should be sized according to water requirement and alternative water heating sources.

Is it suitable for my Requirements?

Biomass can be an excellent supplementary source of heating and can provide a perfect solution to reducing energy bills. However, deciding whether a biomass system is appropriate for you or your project requires consideration of a number of factors. The following are some general principles that will help you decide whether it is a technology you would like to consider in more detail for your property:

Fuel Supply & Quality
Whenever a biomass installation is planned, the intended sources of fuel should always be included in the planning and the equipment specified accordingly. In the UK, pellets are available by the bag and in some areas by bulk tanker. Green Energy Doctor can assist you in finding a suitable fuel supply.

Fuel Cost
A cost comparison with the home’s current heating fuel should be done. Any financial savings would be dependent on a comparison with alternative fuels and on the specific type of biomass fuel used and the regional price variances.

Fuel Storage
Any design must ensure that there is a suitably large and dry area, that is sufficiently close to the intended site of the stove to store the wood or pellets. Green Energy Doctor can advise on a suitable storage area or system.

Flue
If your stove is installed on an outside wall, a simple flue can be used for venting. The vent material must be specifically designed for wood fuel appliances and there must be sufficient air movement for proper operation of the stove. Chimneys can be fitted with a lined flue that is more suitable for a stove insert that would sit in the fireplace.

Location
Choosing the right location to get the most out of you stove is an important consideration. It should be located in an area of the house you want to be the warmest. This is usually the main floor area where kitchen, living and dining rooms are located and where the family normally spend most of their time.

Maintenance
Pellet stoves have a variety of moving parts and motors that require occasional maintenance. It’s a good idea to select a model that gives you easy access to any parts that need care.

Electricity Supply
Although wood burning stoves can operate without an electric power supply, a pellet stove requires electricity to operate by blowing air into the combustion chamber and moving the pellets in. You should ensure a electrical supply is available and also consider that if the power fails, it will stop burning. However battery back-ups are available.

Planning
If the building is listed or in an area of outstanding natural beauty (AONB), then you will need to check with your Local Authority Planning Department before a flue is fitted.

Regulations
The installation must comply with all safety and building regulations.

What Are The Benefits?

Reduce Your Energy Bills

Although in most cases a stove is only a supplementary fuel source, a single unit could provide up to 10% of a typical homes annual space heating requirements if located properly. If the current method of heating that is to be replaced is less efficient, such as an open fire and/or the fuel is more expensive, then biomass stoves can make a contribution towards reducing your energy bill. Savings will depend on how much they are used and which fuel you are replacing.

Reduce Your Carbon Footprint

Biomass contains stored solar energy. When burning wood, CO2 is released, along with a few other by-products of combustion. However, this is largely offset by what was absorbed (via photosynthesis) during the growth of the tree. Heating with wood pellets is thus CO2 neutral. Furthermore, if the wood were to rot, it would release the same amount of CO2 as if it were burnt. A biomass stove which provides a detached home with 10% of annual space heating requirements could save around 840kg of CO2 when installed in an electrically heated home.

Improved Efficiency

Combustion efficiency is a measure of how much of a fuel is converted to energy by an appliance. Open fires are only 25% efficient and so waste most of the energy they create, but modern biomass stoves can offer between 75% to 90% overall efficiency. If you were considering replacing an open fire or a traditional wood burner with a modern pellet stove, the efficiency of your heating source would increase dramatically.

Convenience of Pellets

Modern pellet stoves can remove or reduce some of the manual process that are associated with burning wood. A high-quality pellet stove can turn itself off and on and adjust its burn rate automatically, as needed according to a wall thermostat. They can be lit electrically and the hopper can hold enough pellets for a few days. Furthermore, the higher efficiency of the pellets means that there is less ash, meaning, even with steady use it should only require cleaning out once a week.

Support Your Local Economy Fuels used typically with biomass heating systems tend to have diverse and localised fuel supply chains. UK sourced biomass can offer local business opportunities and support the rural economy.

Improved Energy Performance Ratings For Buildings Using biomass heating equipment in new or refurbished building stock could help to improve its overall environmental energy performance and help it to achieve lower carbon emissions as represented in an EPC (Energy Performance Certificate).

How to Get Started…

To organise a no obligation site visit or to start moving your project forward contact the Green Energy Doctor today on:

T: 0845 009 5652
E: info@greenenergydoctor.co.uk