Biomass Heating FAQs

1. Can a biomass system provide space heating for the home?

For a standard domestic residence, biomass can be used either as wood pellets or logs to provide central heating and domestic hot water, or space heating alone. For space heating, a stand-alone log or pellet stove with flue can be used as an efficient alternative to an open fire.

In order to provide central heating and domestic hot water, a log stove with back boiler can be used, although this does require significant manual input. Alternatively, a pellet-fired boiler can be installed. This will require a much larger amount of space than an equivalent oil or gas boiler; it will have either an integrated hopper that will need to be loaded manually or an external hopper that could be filled by blown delivery of pellets.

2. How 'carbon neutral' is woodfuel, given that transportation, harvesting for coppice etc. has a 'carbon footprint'?

A lot of work has been conducted on the energy balance and carbon requirement of woodfuel and other biofuels. The energy and carbon required in transportation and processing often depends on the end use, but for biomass heating it has been shown that the energy requirement is between 0.088 and 0.106MJ per MJ output and the carbon requirement is 0.005kg CO2 per MJ.* Carbon neutrality will therefore normally be 95%.

*Source: Carbon and Energy Balances for a Range of Biofuels Options, MA Elsayed, R Matthews, ND Mortimer. 2003

3. How do woodfuel heating costs compare to gas, oil and electric alternatives?

Woodfuel is currently (May 2011) cheaper than oil and electricity as a heating fuel and is comparable to gas. The following table shows approximate fuel costs:

Fuel Unit Cost Unit p/kWh
Oil 36 p/litre 3.7
Gas 2.5 p/kWh 2.5
Electricity 7 p/kWh 7.0
Wood (Chip) 90 £/tonne 2.6
Wood (Pellet) 185 £/tonne 3.9

4. Is there enough reliable, long-term local woodfuel supply?

The woodfuel resource from woodland in the Thames Valley is estimated to be in excess of 130,000 ODT/yr (oven-dry tonnes). At present only a very small proportion of this sustainable yield is utilised but it could account for approximately 650 x 500kW biomass boilers. Furthermore, there are the arboricultural residues (e.g. tree surgeons' material) generated in the region and the existing and future planted short rotation plantations that will boost this supply. For further information see

5. In short, what are the differences between wood pellets and wood chips?

  Woodchips Wood pellets
Moisture Woodchips usually vary from 20% to 45% although most boiler will accept a maximum of 30% Wood pellets are usually in the range of 6 – 10% moisture.
Delivery Woodchips will usually be delivered by tipper vehicle and where the store is above ground a method for transferring the fuel to the hopper, such as a chip blower, will be required. Pellets can either be delivered in bags 10 – 15kg bags or in bulk via a blower vehicle.
Storage Preferably chip systems will use an excavated bunker to enable quick and simple deliveries. More often than not the store will be above ground and will require a chip blower. Some pellet boilers will have an integrated hopper alternatively independent hoppers can be used as they hold more fuel. Pellet systems require a third less volume.
Cost Woodchips are cheaper per tonne than pellets but are less consistent in size and moisture. Pellets are significantly more expensive than woodchips but benefit from a higher energy density and ease of handling.

6. What sort of time should be allowed for the design & installation of a biomass boiler?

The majority of biomass systems will have a lead time of 8 – 12 weeks from order to delivery. In addition to this you must allow time for a site visit and design and sizing of the system, which could take up to a month depending on your contractor's workload.

7. What are 'heat supply contracts' and where/when are they applicable?

A heat supply contract enables the end-user to pass on complete control of the biomass system to a third party, usually an Energy Services Company (ESCo). The ESCo will be fully responsible for the operation and maintenance of the boiler including fuel supply and will charge the end-user a price per kWh for the heat used. In some cases a standing charge will also apply. The benefit of this type of contract is that it enables the technology to reach end-users that may not have the confidence or inclination to run the system themselves. It also is a driver for the ESCo to ensure the heat is used efficiently. The heat supply contract option is normally only available to large projects.

8. Why is the moisture content of wood fuels so important?

Biomass boilers are highly engineered combustion systems and are designed to burn woodfuel up to a maximum moisture content. If fuel above the maximum moisture content is supplied, the system will either fail to light or keep going out.

9. Should I have a back-up heat supply and if so, what sort?

A back-up heat supply is an option but is no more applicable for biomass than for any other type of system. Options for back-up space heating include a log or pellet stove. For hot water it is always advisable to have an immersion heater in the water tank.

10. Are there many installers and maintenance companies in the Thames Valley region?

There are no pellet boiler installers based in the Thames Valley but there are several nationwide companies that operate here.

11. How do I work out 'paybacks' on my boiler?

A simple payback calculation will provide a quick but basic insight into the affordability of the scheme. The simple payback can be calculated using the equation:

Payback = Total Cost of Project ÷ Annual Savings

For a very quick arithmetic use today's prices for all energy costs. For a more complex payback calculation it is worth considering future changes in the cost of energy.

12. Can I add the cost of an installation to my mortgage?

Our understanding is that most mortgage companies will willingly increase their offer for the installation of renewable energy technologies. This is a simple way of affording the upfront costs of a system and paying it back over time and is an approach often taken for kitchen/bathroom upgrades and conservatories, so why not for renewable energy installations.

13. Energy Performance Certificates (EPCs) will be needed in the future for all homes at point of sale and rental. How will installing a biomass stove/boiler impact on this?

Installing a biomass heating system is likely to have a major positive impact on the energy/carbon performance of your home and this will be reflected on the certificate. This will, in time, give the home market edge over less well performing properties and add value to the installation in much the same way as having double glazing currently does.

14. Are there grants available for biomass heating system installation?

As of November 2007, the Government-funded Low Carbon Buildings Programme ( was providing the lower of either £1500 or 30% of eligible costs per householder and 30% installed costs to community and 'not-for-profit' groups, up to a limit of 45kW installed heat. These grants are not expected to continue much past April 2008, but new grant schemes may emerge.

Defra have announced that they will be running another round of the Bioenergy Capital Grants Scheme although details of this are yet to be announced. Keep checking

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