An ETA PU7 external wood pellet boiler attached to underfloor heating and an internal domestic hot water tank.
11th July 2013
How it works:
A vacuum turbine sucks wood pellets from the store into the boiler (which has a 30kg pellet storage capacity) where it is burnt and transfers its heat to water via a heat exchanger (the timing of the pellet refill can be set to times to cause minimum disruption). The house has an internal thermostat set for 20°C during the day and 18°C at night. If the temperature falls below these levels the boiler will automatically fire up and send hot water through the underfloor heating. The temperature of the flow is adjusted to take into account the external temperature keeping the house at a steady temperature. For domestic hot water the owners have the boiler set to a daily time to heat a separate hot water tank.
The touch screen controls on the boiler allow for full control of the heating/hot water system and provide information on internal pellet store status, water tank temperature, how full the ash box is, among other things. This control panel can also be synced to a mobile phone/tablet so that you can control it from anywhere.
What was it replacing?
New build property
Who installed it?
Grant/finance received/will receive (FiTs/RHI etc)
Will be applying for the Renewable Heat Incentive. At the current tariff rate of 12.2p/kWh for biomass boilers the household should earn ~£1,210 per year for seven years. This will earn them ~£8,500 meaning that the boiler costs them £6,000- which is fairly equivalent to the price of an efficient oil boiler and will be cheaper to run.
Any planning issues:
As it was a new build they had to make an amendment to the building warrant, which was passed with no issues.
Inconvenience/disruption levels of installation:
The owners had installed the underfloor heating pipes themselves (following a design created for the house by Nu-Heat). Renewables Now installed the pellet boiler and connected it to the underfloor heating and the hot water tank. There was minimal disruption and took 3 days to install.
None and the owners report that there is hardly any smoke from the flue.
The boiler will require an annual service costing ~£175 +VAT. Every 20-30kg the boiler self-cleans the ash from the pipes and combustion chamber, this results in the ash pan requiring to be emptied every few months (the ash can be used on the garden or put in the compost bin). Bags of 10kg wood pellets are manually topped up into a storage container (right) and then the boiler feeds itself. During the summer it uses approximately 26kg of pellets a week (£6.37) and during the winter 84kg (£20.58 @ £245 a tonne sourced from Pentland Biomass). This amounts to around 3 tonnes of pellets burnt annually
The owners had wanted to install a green heating system in their new home and considered both air source heat pumps (ASHP) and pellet boilers. The ASHP was quoted as slightly cheaper to install so they decided to go for this option. However, when Renewables Now came to the house for the initial assessment they found that the underfloor piping had been designed and laid to suit a temperature of 55°C- which would be too hot for the ASHP to work efficiently. Therefore the owners returned to their original thinking of the pellet boiler. They knew they wanted an external system and the ETA PU7 came recommended by Renewables Now (one of them had it in his home).
Recommend the technology:
If you would like to speak with the owners about their project, please contact Michael or Barbara Bond- [email protected] or 01397 713914