The Abernethy Trust is a Christian educational charity which runs outdoor adventure centres in Scotland. They contacted Dunster to investigate the feasibility of installing a small district heating network for a group of holiday lodges and a pair of staff cottages.

Following a site visit and discussions, Dunster’s scheme to replace the electric heating systems in the properties with heat from a wood pellet boiler installed in an existing garage was accepted. The Trust undertook the initial renovation of the garage, which was in a poor state of repair, after which Dunster installed a bespoke pellet store to make the most of the available space, along with the biomass plant and the distribution pipework.

Dunster designed and installed the interface with each property to allow fully independent control of the heating and hot water supply and worked with the Trust’s plumber who installed the new radiators, hot water cylinders and associated pipework inside the buildings. The installation was carefully phased to minimise disruption to the lodges whilst ensuring that commissioning and RHI accreditation was achieved as soon as practical.

Fuel Supply

A bulk pellet store has been built into the end of the garage with a V-shaped floor and a multi-point vacuum extraction system. The boiler has a ‘day hopper’ which it fills automatically when required and from which it feeds the boiler. No fuel handling is required by the client. About 4 times a year, a pellet tanker delivers fuel to the system by pumping pellets through hoses connected to the filling points outside the building. The boiler does not need to be shut down during filling operations and no access to the plant room is required.

System Design and Installation

Dunster worked with the Trust’s plumber to ensure that the new radiator and hot water systems installed operated seamlessly with the biomass boiler to maintain maximum efficiency and minimise losses in the external pipework. The 1,500-litre thermal store allows the biomass boiler to operate at peak efficiency even when demand is low in the summer. The networking of the controls ensures that water is only pumped around the system when required, further reducing losses, and allows remote monitoring of the system and reading of all the heat meters over the internet which greatly simplifies billing and data recording.


September 2015


Heating for 3 holiday lodges and 2 staff cottages

Boiler and plant

70kW wood pellet boiler with 1,500 litre accumulator tank and 6 tonne pellet store. The plant room and fuel store are housed in a converted single garage attached to the staff cottage.


The boiler is burning about 20 tonnes of pellets per year to satisfy demand from the properties.

Fuel delivery

A commercial pellet supplier is used to blow wood pellets into the bulk store. Pellets are transferred to the boiler using a vacuum transfer system.

Grant / Funding

The project was self-funded and is fully accredited on the non-domestic RHI scheme

Savings / Investments

Although the project was undertaken primarily for environmental reasons, income from the RHI and sales of heat to the lodges is resulting in a return on investment of around 5%.

CO2 saving

More than 30 tonnes per annum compared to the previous electric heating systems.

We chose Dunster as they came highly recommended and provided a competitive quote with great detail. Their work was carried out on time and to a high standard. The equipment has proved to be very reliable with minimal maintenance required. The system replaced electric heating resulting in warmer properties that are costing less to heat.

Pete Moore, Abernethy Trust Deputy Operations Director