biomass and heat pumps, energy-efficient buildings

We've been installing biomass boilers and heat pumps since 2005, as well as hybrid systems, combining biomass with oil and solar hot water.

Wood pellet boilers burn a less costly and renewable fuel

Pellet boilers are an automated, efficient way to burn wood.  The fuel is delivered in bulk or bags, in a standardised form, just like oil or LPG, and the ignition process is automatic.  Emptying the ash is not automatic, but it doesn't need to be done very often.  Provided the pellets are sourced from sensibly-farmed trees, this fuel is genuinely renewable.

At the moment, the cost per kWh, or unit, is considerably lower than oil.  If you buy in bulk it can be 40-45% lower than the cost of oil.

Pellet boilers come in a range of sizes to suit houses or commercial and industrial buildings.

There's no denying that the installation cost of a pellet boiler is quite high by comparison with an oil boiler, but over the long term, it makes sense.  They need quite a lot of space if they have a bulk fuel store, and there needs to be a route for the flue pipe, so they're often installed in an out-building of some kind, or a shipping container.  Space is sometimes needed for a buffer tank, which can range in volume from 500 to several thousand litres.  Pre-insulated pipe can be used to deliver eneergy over quite long distances or to a group of buildings.

At the moment (April 2014), there is a subsidy for biomass through the Renewable Heat Incentive - the RHI is available for commercial systems now and for domestic systems.  On OfGEM's website, you will find documents giving the details what is and isn't eligible.

We are accredited under the Microgeneration Scheme (MCS) to install biomass boilers.  Our MCS number is NIC5061 and it applies to MIS3004, the standard for biomass systems.

Wood chip and fan-driven log boilers, hybrid systems

For larger boilers, generally over 200kW in output, burning wood chip, rather than pellets, is an option.  Wood chip is cheaper than wood pellet There are European standards for good-quality chips as well, which is important to keep the boiler running smoothly.

If you've got access to lots of logs, a modern log boler is an efficient way to burn them.  Because they heat a large tank, called an accumulator and as close to automated as you'll get with

A hybrid system takes advantage of several heat sources, normally logs, oil and thermal solar.  To qualify for the domestic RHI, hybrid systems may need a heat meter.

In the longer run, all of these technologies are economically viable without any kind of subsidy..

Energy-efficient buildings

We have designed and built a series of highly-insulated buildings.  The principle is to make the building easy and pleasant to live in, by keeping the energy in and the air fresh.  Take a look at the photos, which show a couple of examples.  For these projects, we work with the client to arrive at the design, then with a team of specialists to provide the construction skills.

Cae'n y Mynydd, Llangadfan - dyluniad a prhif gwaith gan Gwres Glas - Green Heat


Hen ysgubor sydd erbyn hyn mewn cyflwr cystal ac yr oedd yn ei ieuenctid. Mae trwch sylweddol o ynysiad oddi fewn, er mwyn rhoi chwarae teg i'r pwmp gwres, ac mae'r awyru mecanyddol yn adennill y rhan fwyaf o'r gwres o'r awyr wrth iddo gael ei gylchu.

This barn was renovated and converted to provide an office space.  It's insulated very thoroughly and needs mechanical ventilation when the doors and windows are closed.  The ventilation recovers most of the heat from the outgoing air, which means that the load on the heat pump is minimal.


Hen ffordd Gymreig o fyw gyda thechnoleg cyfoes.


Bryn Awel, Llanfair Caereinion



This shot shows how much fun you can have installing the ventilation pipes, before insulating the loft with around 200mm of sprayed-on polyurethane foam, which formed a continuous windproof skin over the whole loft.  The loft hatch was built as a hermetic, warm plug.


Fuel feed lines (red & grey tubes), flow and return pipework and temperature sensor for heat meter, on a 100kW pellet boiler


Large tank (accumulator) for a hybrid system combining a 40kW log boiler with 5 solar panels and oil-fired backup.

Bryn Awel, Llanfair Caereinion, design and build by Gwres Glas - Green Heat

Renovation and extension of a house built in 1975.  It's now 30% bigger but needs 5 times less heat than before the renovation.


External insulation on the original building.  Highly-insulated extension.



The original brick was is very porous and several houses on the estate suffer with damp, as rain penetrates the brick skin and finds its way through the cavity insulation.  For Bryn Awel, the external insulation provides a waterproof external skin to solve this problem as well as keeping the heat in.


Heat is from a 4kW Kensa heat pump.  The photo below shows part of the ground array, known as a slinky.  Hot water is from the heat pump and a thermal solar panel.

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