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If you're not sure about renewables, nothing beats seeing them in situ

Posted by Gordon Glass on 31 August 2012 at 9:35 am

The unfamiliarity of a lot of new technologies such as biomass boilers, solid wall insulation, heat pumps and solar panels puts many people off the idea of installing one. Seeing one working in someone's home, and being able to ask questions about how they find it can make all the difference.

If you are excited about the potential of biomass, you may be considering a wood pellet boiler. Mark Brown has just such a boiler installed in the garage of his 5-bedroom house in High Wycombe, as I discovered on a recent visit.

Mark says that, of all the technologies you can install for heating, biomass offers the greatest reduction in carbon footprint per £ spent. It’s a resilient technology as locally-sourced biomass may be used.  

My own first impression of Mark’s Austrian-made boiler was that this is serious piece of modern engineering. Apart from having to pour pellet into the hopper, it is fully automated and can be literally put on a timer. It can even control the existing gas boiler which serves as a backup.

A couple of things surprised me. You’d think ash might be a bit of an issue. "Not so," says Mark. You are talking handfuls, not bucketfuls - in fact, he empties the ash just once a year. And smoke - you can neither see nor smell any! That’s amazing.

But only when you see this biomass boiler in situ do you start to realise the importance of getting a sense of the dimensions involved - not just for the boiler, but also for storing 3 tonnes of wood pellets. It’s significant.

But, don’t take my word for this. Mark’s is just one of seven SuperHome households with biomass boilers hosting free open days this September. I think it’s hard to beat visiting an owner like Mark to get a proper idea of what living with one of these systems means - both the benefits and the challenges.

To find out more, or to book a tour, see the SuperHomes website.  

SuperHomes are older homes refurbished by their owners to reduce CO2 emissions by at least 60%. 50 home owners will be opening their doors in September. SuperHomes often use alternative heating sources like biomass boilers, air source heat pumps or solar thermal. Mark has written more about his system here, and it is also possible to visit his home by appointment. He has also installed solar thermal and PV panels, insulated lofts and cavity walls, installed double glazing and low energy lighting, and thoroughly draught proofed the house. 

About the author: Gordon Glass is the online marketing manager of YouGen and SuperHomes.

If you have a question about anything in the above blog, please ask it in the comments section below.

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11 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 4 September 2012 at 2:42 pm

Thank you Mark, lots of interesting info here.

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Mark Brown

Mark BrownComment left on: 3 September 2012 at 6:12 pm

Not everyone agrees. This website from Feb 2012 inverts this conclusion. Seem to depend much on how you add in the overheads and efficiencies?

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Mark Brown

Mark BrownComment left on: 3 September 2012 at 6:08 pm

Might have answered my own question with a quick search on Google. Gound this:,59188&_dad=portal

This suggests that Gas is 4.8p/kWh whilst Wood pellets are 4.2p/kWh. Heating OIl is now 6.0p/kWh.

So my data may be out of date with fuel oil and gas price rises outstripping rises in wood fuels.

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Mark Brown

Mark BrownComment left on: 3 September 2012 at 6:04 pm

Another update (busy day!). By coincidence I had a local Biomass Boiler company at Superhome59 today for the annual checkup and service of the KWB pictured in the above blog by Gordon. So I raised the question of firewalls. The technician looked puzzled by the idea and told me it was unneccesary. The reason he gave was that the British Standards applying to biomass boilers stipulates that only a 15cm airgap is required if the external casing is less than 100C. A bigger airgap is required if over that temp. His concern was more that stored pellets get damp easily. He saw no specific fire hazard.

The caveat given by my advisor was only that the rules are open to interpretation. It was possible that buried in the Building Regulations somewhere there was contrary advice. Maybe someone out there could comment?

My second question is about the price per kWh equivalent in 2012 of Gas versus Wood Pellets and other fuels. When I was writing the core article that Gordon Glass is quoting (in the above blog) I was using the economics of 2009. My friend from the Biomass Maintenance Company today reckons that wood pellet is now cheaper than gas (although capital costs remain some 4 to 10 times more expensive to install). Anyone know how true this is today in 2012?

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Mark Brown

Mark BrownComment left on: 3 September 2012 at 10:34 am

Just to add: the separation between the biomass boiler and car is about 1.1m (45inches) at a minimum at any time. Gas Boiler separation from car is about 1.5m (60inches or 5ft).

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Mark Brown

Mark BrownComment left on: 3 September 2012 at 10:27 am

I can answer the question about firewalls (but this is not authoritative as I do not know what the LEGAL or H&S guidelines are.) I too would like to know the proper guidelines. As you can see from the photo (taken in my garage) the wood pellet bags and car are next to the boiler. I asked my installer what the separation should be between boiler and wood pellet stack. He recommended a 30cm air gap (but I had the feeling he was just making it up). However this is a commonsense suggestion to stop the wood fuel from touching the boiler. If it does it could get hot which increases the risk of combustion. I have seen a report on the BBC News a few years back showing biomass boilers in a new housing development that showed a stack of similar wood pellet bags next to a boiler. No "firewall" was evident.

So paranoia is not justified (it would drive you mad and you wouldn't do anything) but commonsense caution should be exercised. IF the boiler went up in flames then you have to consider the fact that it is inside the body of my home. Hence the presence of wood fuel near to the boiler doesn't add any significant risk (the fire would burn for longer but there is no explosion risk from it). It is the source of ignition that is the issue. The garage itself is "NORMAL" in that it contains a car. The greatest risk of combustion may actually be the vehicle not the boiler! For this reason I installed a fire extinguisher - a powder one suitable for putting out an electrical or petrol fire.

The garage also contains a regular gas boiler... What is the risk of this exploding? In fact have you heard of this ever happening? The KWB is a domestic unit tried and tested. So let us assume that the risk of ignition from the 2 boilers are the same. Hence risk may be doubled but is still very low. So we might as well ask: "should I put a firewall between my gas boiler and the gas pipe?"

All technologies come with an element of risk. Your average car is extremely dangerous yet are we having this conversation about the autogas-powered Toyota Aygo? Note - the pictured car has a pressurised LPG tank in the boot! As I say, we have the right to be cautious: we are stacking the risks of two boilers and a car in a confined space. BUT I do not believe that a physical firewall between a stack of wood and a boiler is necessary. Just give it a good 12inches separation between ignition sources and fuel storage. An air-gap is adequate. Get a fire extinguisher and put it somewhere where you can get at it without being anywhere near the boiler. In the final analysis ensure your personal safety at all times by makng sure you have an evacuation strategy that doesn't require exit past the boiler. It is all commonsense. It may be subjectve but I can only add, from personal experience, the fire risk simply doesn't bother us. It no more crosses our minds than the thought that the petrol tank in the car may explode when we go for a drive.

If you want an authoritative answer I suggest approaching the manufacturer not the installer. European manufacturers have years of experience but the installer industry is still very immature in the UK. Most of them have only installed in larger buildings where they may have had the luxury of a separate fuel storage area. These small biomass boilers have a hopper for the fuel right next to the boilers separated by a a few mm of steel panel. The boiler itself is well insulated so only gets warm to the touch on the outside during use. The answer is implicit in the manufacture of the device. Our experience shows that the risk is very minimal. It simply doesn't concern us.

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Ian Smith

Ian SmithComment left on: 3 September 2012 at 9:08 am

This example raises the question about installing such combustion devices in garages if cars (petrol or diesel ones) are also to be housed in the same space without firewalls.   I was told by an installer that a firewall would be needed.  When one left space on the boiler side of the firewall to access the boiler for maintenance, the footprint in the garage became unacceptable.  Are firewalls required in these circumstances?

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Cathy Debenham

Cathy DebenhamComment left on: 3 September 2012 at 8:16 am

This is a good question Ian. I don't know the answer, but I'll do my best to find out, and we'll do a blog on it.

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gordong156Comment left on: 31 August 2012 at 12:51 pm

True - luckily there are numerous local green home initiatives hosting free Open Days between 6th-9th September including GreenDor in Dorchester, EcoHab in Cheltenham and Forest Eco Open Homes in Gloucestershire. See Heritage Open Days for more.

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JonasComment left on: 31 August 2012 at 12:27 pm

To see other real examples of installed biomass boilers and to meet their owners (for free!) - take advantage of the Suffolk Green Buildings Open Days event taking place between 6-9th September. This is a Suffolk Green Buildings Network event, supported by Suffolk County Council abnd UCS, featuring 15 different buildings across the county of Suffolk. For more details go to

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Cathy Debenham

Cathy DebenhamComment left on: 31 August 2012 at 11:56 am

Click here to read about other open eco homes schemes in September.

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