OkoFEN Pellematic PE(S)25 biomass boiler review by John Whitehead

John Whitehead with his OkoFEN boiler

John Whitehead with his OkoFEN Pellematic PE(S)25

John and Ceilia Whitehead chose to install the OkoFEN Pellematic PE(S)25 as part of the energy efficient improvements they made to their eco guesthouse. Here engineer enthusiast John shares their experience of the product.

OkoFEN’s PE(S)25 biomass boiler

The OkoFEN Pellematic is a fully automatic wood pellet biomass boiler. Each model in the Pellematic series comes with Efficient Performance Control Technology and can range from 10kW to 32kW of power output. The boiler consists of three main parts: combustion chamber, hopper and ash tray box. This high performance boiler comes in a variety of sizes and options to suit almost any home. It has a number of functions, including remote control capabilities via a smart phone application and the Pellematic Touch controller.

John says…

It’s not cheap but it’s superbly engineered and has an outstanding performance.

We decided to install OkoFEN’s PE(S)25 biomass boiler in 2011 as part of the ongoing refurbishment to our eco home in beautiful Snowdonia, Wales. This machine is superbly engineered and provides 25kW of power output to effectively heat our eight bedroom home, which also serves as a year round guesthouse. It works as a wood gasification boiler, burning wood pellets to create a gas which is then efficiently re-burnt in a central combustion chamber at over 900°C. In addition to the boiler, we also purchased OkoFEN’s KGT2620 Flexilo Compact – Fabric Tank… in other words, a big bag to store all the wood pellets! We chose the 6 tonne option, although the capacity of these fabric tanks can range from 450kg to 12 tonnes. These tanks are great at compactly storing the pellets free from moisture, however at six foot tall and as big as a car, they’re rather large, so keep this in mind.

The PE(S)25 has a built in computer that is fitted with modular heating circuits made by PAW. Full weather compensated controls monitor inside and outside temperatures and tell the boiler if and when it needs to kick in, adapting the heat it produces to changing weather conditions. This not only gives a better performing boiler, but also helps reduce annual pellet consumption.

This particular boiler is an excellent option if you already have or are considering other energy efficiency measures. Our boiler is seamlessly integrated with four solar thermal tube arrays we have located on the roof of our boiler house. The boiler’s computer will automatically decide how much heat is needed in order to balance the fluctuating solar output. For an engineer like me, this is the stuff we dream of!


It wasn’t hard to find a local installer.  Most importantly we needed someone who could integrate the boiler with our solar thermal system.

After many years of visiting energy conventions and looking for the right product, we settled on the OkoFEN. Believing local is best, we chose North Wales based company Menai Heating to install the boiler, who were recommended to us by Organic Energy. We are a carbon neutral guesthouse and have a keen interest in this field, so already knew about different installers in the local area. Menai Heating was especially suitable for our project as they were qualified to integrate the solar thermal and boiler systems.

The boiler was fitted into the newly purpose built boiler house, located at the gable end of our guesthouse. Because of the sheer size of the boiler and fabric tank, it was necessary for them to have their own room. However, this won’t always be the case for everyone, it really depends on the available space you have and the size of boiler you choose. Naturally the boiler house is warm. We still benefit from this heat as it radiates through the huge 39 inch granite wall that acts as a thermal sponge passing heat through to the house.

The work was carried out over a 10 day period and we feel the £20,000 cost was definitely worth it. The installation went smoothly and we are extremely happy with the support our installer continues to give us. No planning permission was required to install the boiler itself, but as expected, building the extension for the boiler house did need permission.

The PE(S)25 is fueled by carbon neutral 6mm wood pellets. We source these from a local saw mill who create them as a sustainable by-product. Although there are cheaper alternatives on the market, we opted to stay clear from imported pellets. Our research has found that problems with biomass boilers are usually associated with the pellet used, so a good quality pellet is essential. Our fuel is delivered by lorries which, without any mess or odour, blow six tonnes of pellets directly into the storage tank. The whole process takes about 25 minutes, providing enough fuel to last us roughly 14 months.

Main benefits

You forget about it, it just works.

 The main benefit of the OkoFEN PE(S)25 is the eco-efficient performance it gives and the way it automatically replenishes burnt wood pellets. We were previously using a 26kW log burner to heat our home. This worked well so long as you kept feeding it every hour, which worked out about two wheel barrows of wood every day. This meant it was consuming 17 tonnes per year, significantly more than the six tonnes of processed pellets we now require. Burning huge amounts of wood brings complications of seasoning and storing it for long periods before it can be used. Now we no longer need to put in the time and hard graft that comes with using a log burner as your primary heating source. We simply relax and let the boiler automatically refuel itself, which as we get older, will become a benefit that we appreciate even more.

The product also qualifies for the government’s Renewable Heat Incentive scheme. We receive payments of about £1400 a year, meaning we will have recouped the entire installation cost within 11 years. Having a financial payback is of course a huge benefit, and one that makes facing the large upfront cost slightly easier!

We are extremely happy with the OkoFEN PE(S)25. Its level of power efficiency (93%) is simply outstanding. It saves a significant amount of carbon emissions in comparison to conventional boilers, and keeps us free from dirty fossil fuels – a lifestyle we are committed to lead. Satisfying our guests by ensuring they always come back to a warm and comfortable environment after a day out on the hills is a top priority. The OkoFEN always delivers, providing the heat and hot water we need.

Practical details

Totally automatic with a 5 minute ash empty on the garden every six weeks and a 25 minute blown bulk pellet delivery every 14 months.

Practically the boiler is easy to use and control, requires very little attention and is extremely reliable. In the five years of having the product, the only problem we’ve experienced has been a minor jam from wood pellet dust. It comes with a five year guarantee and has a lifespan of at least 25 years.

From an aesthetic point of view, the PE(S)25 looks great. The only thing I would say is that because of its size, the KGT2620 fabric tank can sometimes look a little imposing. For this particular reason I would suggest that the large auto feed bags are best suited for larger homes (four+ bedrooms), that have a double garage or out building. However, if your house doesn’t meet any of these criteria, don’t be put off, much smaller storage options are available.

The need to empty the ash box is kept to a minimum because of the highly efficient use of the wood pellet fuel. This means maintenance is not regularly required. We simply have to empty two buckets full of ash when the boiler’s computer says it’s full. This is an easy process that takes place every six weeks or so. Each night the boiler turns on its self-cleaning mode, destroying any tepid water and maintaining a clean burn needed for maximum performance. Just to give you the heads up, this cleaning process can often bang and clank, which can be a little spooky on a dark winter’s night. On top of this we get it professionally serviced every two years, as recommended by the manufacturer.


Just trust me, it is good.

It was early days for wood gasification in the UK in 2011, which meant we initially we found it very difficult to find enough product information to help us make our decision. After much research we would say that our top three considerations when comparing similar products are engineering, reliability and local supplier. In comparison to other brands and models in its category the OkoFEN PE(S)25 is at the top of the price range. However, we strongly feel the price is justified by its consistently outstanding performance and green credentials. It also stood out to us because of the quality of its build and engineering design. But if we had to change anything about it, we would only wish for it to be slightly cheaper and made locally.

Product details: OkoFEN PE(S)25
Highlight Manufacturer: OkoFEN
Installer: Menai Heating
Supplier: Organic Energy
Owner Case Study: SuperHome 154

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