Are biomass boiler costs justified?

Biomass boiler costs don’t end with installation. Mark Brown takes a frank look at the pros and cons of a biomass boiler for a 5 bed detached house.


Biomass boiler installation

Wood Pellet Boiler Installation at SuperHome

Biomass boiler installation was largely trouble free but took longer than anticipated

Work started in the warm August of 2009 when we didn’t need heating. Hot water was supplied by an immersion heater as we didn’t have the Solar Thermal panels up at this point (they came in 2010).

The estimated install was meant to be two weeks but it took six in total. We allocated one half of a double garage to the project in an area co-located with the existing gas-boiler for convenience.

Installation was largely trouble-free. The UK representative of the Manufacturer (KWB) came out for commissioning and observed that one section of pipework was incorrect. It was quickly rectified.

We live in a Conservation area and had planning permission refused for an external flue so we had it route through the corner of the bedroom over the garage. Not a big problem as our installer arranged for builders to come in and box in the flue. We redecorated ourselves.


Biomass boiler system

The KWB Easyfire is a 15kW boiler with a 500l buffer tank. The system provides space and water heating but we also have both gas backup as well as solar thermal and lounge wood stove.

Our system is using wood pellets fed from a hopper. The hopper stores enough for at least seven days in the depth of winter but can last up to two months in a warm summer. It is fully automated, other than filling it up with pellets or emptying the ash (once a year!) no work is required. Our KWB is very reliable.


Biomass boiler costs

Wood Pellet System at SuperHome

This KWB Easyfire 15kW biomass boiler cost £15,590 installed

We installed in 2009 on the assumption that the Renewable Heat Incentive would pay for the investment. We could have had a cheaper boiler make but had to opt for one licenced for use in a smoke-control zone. Total cost of the boiler, buffer tank, flue, labour & VAT came to £15,590 minus £1000 from the (then) Low Carbon Building program grant.

We use bagged wood pellets and need just under 5 tonnes a year. They cost about £230/tonne (delivered + VAT) working out at £1100 pa approx. We take three tonnes per delivery with about two deliveries a year. Note that there are slightly cheaper options but we prefer UK-sourced pellets.

We are lucky enough to have a maintenance contract that covers five years’ work. It works out at about £150 a year this way, but you could pay up to £500 pa if unwilling to pay up front for a contract. This contract includes cleaning the flue and boiler.


Pros and cons of biomass boilers


  • Of all the technologies you install for heating biomass offer the greatest reduction in carbon footprint per £ spent
  • The KWB we used is able to control the existing Gas boiler and use it as backup
  • Biomass boiler installations cause no more disruption than would maintenance on your regular boiler. No need to rip up your floors or garden as you might for a ground-source heat pump installation.
  • Biomass boilers use very little electricity
  • Biomass boilers can use waste wood (turned into pellets)
  • Biomass boilers can use locally-sourced biomass helping your local economy
  • Biomass boilers are a resilient technology when used with other local microgeneration such as photovoltaics
  • Biomass is very clean – you cannot see nor smell any smoke – ever!
  • The ash from a biomass boiler takes up hardly any space. When necessary tip it on your garden as fertiliser.


  • Biomass boilers are expensive coming in at anything upward of £9000. You could get quotes for well over £20,000 so shop around. Even if replacing oil it is hard to see a payback without an additional incentive such as the RHI or a cheap on-site source of fuel such as wood chip.

    Wood pellet storage at SuperHome

    A double garage provides ample storage but moving and stacking bagged wood pellets requires physical effort

  • It was really hard to find a domestic installer (or was in 2008/09).
  • Don’t forget you will need a buffer tank and storage space for the fuel. We suggest allowing the sort of space in which a small car would fit.
  • Biomass boilers are not really suitable for small homes on the gas grid. They are more beneficial if you have a very large building (ie, farm house, community hall, church, school, etc.) off mains gas.
  • Biomass fuel will cost as much as using Oil so there are no direct costs savings if you are on mains gas.
  • Your Biomass boiler deserves to be maintained properly. The UK market is only very slowly gearing up so you might be limited in choice. Your average Corgi registered plumber will not touch it.
  • Our KWB boiler’s controllers are sophisticated to the point of being too complicated. Refuelling from bags can be physically demanding. This makes them unsuitable for social housing, the physically impaired or the elderly.
  • Fuel delivery can be inconvenient (as for any solid fuel) so we normally take the day off work or pay extra for Saturday delivery. Delivery to narrow cul de sacs are a problem in our experience so we always specify a small 8 tonne truck – sometimes this message doesn’t get through and we have had to push pallets from the road on a pallet trolley with the help of the delivery driver. This is almost impossible for a one tonne pallet, we recommend ¾ tonne pallets or less. A tail lift truck is recommended. We always end up part-hand-stacking some of the load to reduce its footprint in the garage. For one fit man this might take 40 minutes to shift 1.5tonnes of bagged pellets (15kg per bag). The other option is to use a large hopper with the pellets blown in – but this is only suitable for much larger installations than we have.
  • Having solar thermal can mean the biomass boiler is hardly used through part of the summer. However it will keep the buffer tank up to operating temperature which is wasteful (although this can be switched off). Our system was sized appropriately based upon our SAP rating so this isn’t a significant problem.



Given the information we had in 2009 (and the pending Renewable Heat Incentive) we think we made a good choice. However the RHI has not materialised and, as far as we know, might NEVER pay us a penny for this boiler in its final manifestation.

When deciding upon this form of heating we did compare it to a ground-source heat pump. We didn’t cost up a comparable GSHP but it would only have been suitable if we had been prepared to dig up the floor for underfloor heating plus the garden for the ground loop. A GSHP would need a lot of electricity to run but we wanted to generate most of our own power so it would have put that objective out of reach. Hence biomass was the most local & resilient option.

We have great satisfaction with the boiler and our only regret is the loss of space in the garage. We would recommend domestic biomass for rural areas with large buildings off mains gas.


Find out more – visit a refurbished home

You can find out more about biomass boilers at green open house events in September. Speak to real homeowners as they share their personal experience of refurbishing their homes as part of SuperHome Open Days. SuperHomes are older homes refurbished by their owners for greater comfort, lower bills and far fewer carbon emissions – at least 60% less! Entry is free. Book now.

Also See:
Green boiler
Are heat pump cost-effective?
Interstitial condensation
Draught-proofing- a good thing?

Further Information:
Full details of this project are available at Post Carbon Living. You can see this wood pellet boiler in situ at Mark Brown’s SuperHome at Open Days in March and September or by appointment. Mark is a member of Transition Town High Wycombe.

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© Mark Brown Aug 2012