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14 things to ask your biomass boiler installer

Posted by Jon Edge on 3 November 2010 at 9:20 am

Biomass is still pretty new to a lot of people in the UK. However, it is a tried and tested technology, used successfully for many years in other countries. Biomass boilers are a modern and very low carbon alternative to fossil fuels, especially oil or LPG and will give you as much heat and hot water as you want, so long as the right system is designed to meet your needs.

1.The first things to ask is whether they are MCS certified installers with MCS approved products (under 45kW outputs currently and probably higher once confirmed) as this will mean you can claim the Renewable Heat Incentive (RHI) when it launches in June 2011 (NB: final details are not yet confirmed).

2. Which fuel source works best for you? Log, chip or pellet? This can be a tricky one to decide but your installer should talk through everything and give you all the variables which will then show the best product for you. There is a best fit depending on a number of factors, such as size and if you have your own wood supply or access to wood.

3. Do you want the full automation of pellet (but have to buy in pellets), or the cheap and available fuel of logs but have to stoke them (only once a day for electronically managed boilers) or if the size demands it the automation and low cost fuel (but higher capital cost) of chip

4. How much space do you need for fuel storage? Wood chip needs the largest storage space next to the boiler room, pellet has the highest energy density per volume and vacuum fed pellet boilers can be about 20 metres away from the wood store. Logs need cover to be seasoned, but don’t need to be next to the boiler. Ideally for chip or pellet you would minimise deliveries to only one or two a year.

5. What boiler size/output will I need? The installer should do heat load calculations on your site and this determines the size of the boiler. It is important to know how close the boiler size is to the heat load and to ensure it is not under- or over-sized. Under-sized boilers will have to work too hard and may not give enough heat, and over-sized boilers will cost more than is necessary and not run at full efficiency (short cycling).

6. Is it a computer controlled boiler? With modern and computer controlled boilers there are sensors and clever things going on to regulate and control your heating. Weather compensation will take indoor and outdoor temperature readings and alter the temperature in your heating and hot water as a result. Also if you have solar thermal too (a great idea with biomass) then a sensor in the tank ensures solar hot water is used before the boiler fires again, making the most efficient use of the energy.

7. Do I need a buffer/ accumulator tank? Buffer tanks are large and highly insulated water tanks that act as a heat store and give instant hot water if the demand is high. Some modern pellet boilers will plumb straight into underfloor heating or radiators but log and chip boilers need buffer tanks. They add cost to the project but it makes sense in many cases and can allow for a slightly undersized boiler if there is a buffer tank to take the strain

8. How much wood fuel will I need? This will depend on the size of the boiler (output in kW) as well as the size and heat demand of the property. Energy density of the fuel as well as the type of fuel also affects quantity, space needed and cost of fuel. There are calculations that the installer can do to give you a tonnage per year and wood fuel information and average prices can be found at the Biomass Energy Centre.

9. Will my installation be fully plumbed into my existing heating system? This is an important factor to bear in mind. Do you want the complete installation finished by your biomass company, who only leave when everything is commissioned and working? Or will they only supply the boiler and then leave you to find a plumber?

10. Does it have a Lambda probe? A Lambda probe is a sensor that monitors the oxygen content of the exhaust gases and can adjust vents accordingly to maximise the efficiency of the burning chamber and minimise emissions such as Carbon Monoxide. Boilers with Lambda probes should be eligible for use in smoke free zones as a result of these very low emissions and very high efficiencies.

11. What kind of back burn protection does it have? The modern, automatically-fed biomass boilers should all now have some form of protection to ensure no fuel can catch fire before it reaches the furnace. It is worth checking though, just for peace of mind.

12. How much automation do I want? There is a wide range of biomass boilers on the market, from different regions, with different features, designed for different purposes and people. Some of the factors to bear in mind are: how willing you are to get in the boiler to light it, clean it, fix it and control it? There are boilers with high build quality, self-cleaning, self-lighting and fully programmable, even with web and smart phone access to control remotely. There is always a cost/benefit analysis to do for these features, which over time may be worth the extra cost, especially with the higher build quality that often comes with the more advanced biomass systems.

13. What do I do if I go on holiday? With a log boiler, which needs to be manually fed then the boiler will go out, but residual heat can last in the buffer tank for a while and it will just be potentially cold when you return until the boiler is fired up again to warm things up. With chip and pellet they are fully automated, so can just run an automatic programme

14. Can I burn other fuel sources? This is one to research if you want to burn Miscanthus for example, as this has been notorious for clinkering and breaking boilers, or at least damaging and dramatically lowering the efficiency of them. There are some boilers which use gas recirculation kits and other clever ways to avoid clinkering, but it is worth checking with the manufacturer or trusted installers if you want to use any exotic fuel types. As a general rule untreated wood is the best fuel source. Wood gasification or log boilers can take off-cuts, timber, chip, pellet and sawdust through the furnace door, however a recipe or mixture is advised to balance the burning. There should never be any wood which has paint, varnish, glue or any other additives as this could produce harmful emissions and damage the boiler. Chip and pellet should be bought at the correct moisture content and without any harmful substances in.

Picture by Faith Goble

More information about biomass from YouGen

Biomass information page

6 things to consider before buying a wood burning stove

Is there enough wood in the UK for biomass?

6 tips for finding the best log supplier

Find a biomass boiler installer

About the author: Jon Edge is marketing director at Fair Energy CIC

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

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6 comments - read them below or add one


BakermanComment left on: 16 December 2014 at 10:07 am

I have read you tips for Biomass boilers. And point 7 regarding Buffer tanks. I have been advised to have a buffer tank by my installer but my piumber, who worked on my current sytem, says its not nececssary. I am looking at installing a Grant Spira 26kw biomass boiler. Does the buffer tank  add to efficiency or is it just a convenence storing hot water? My currebt oil boiler works fine for my needs, what would be the difference with the buffer tank? I would like to save the money but not at the expense of losing efficiency . 

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DelBoyComment left on: 18 September 2014 at 3:03 pm

Good advice but I have one more very very important one to add


Ensure that the installation company checks the power supply is adequate before you part with any money.  I ordered a 130kW biomass boiler and onlu during installation was it discovered that there was insufficient power to run the inverters as no 3 phase was available.


£10k to bring power to site from a neighbours farm 220m away.  Between a rock and a hard place I have to pay for the new supply as the installer says "We could not be expected to know power was inadequate"

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GlenfenderComment left on: 8 February 2011 at 2:37 pm

A very good summary.  Only point I would add is that some boilers (like the Okofen) are designed to operate very efficiently without a Lambda probe.  I understand that one problem with the Lambda probes is that they are prone to failure and expensive to replace.  

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aishamillerComment left on: 30 December 2010 at 9:24 am

Nice post. Keep up with your good wood work.

Thank you.

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wow  . it tells really many things to know when we have biomass biomass boiler to do. The biomass boilers are installed all over the country and supplies woodchip to a large area.

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Between the Green

Between the GreenComment left on: 17 November 2010 at 6:32 pm

Hi, Jon. When you say wood fuel should be free of "any other additives", what exactly does this mean? I use offcuts from timber used for making fences, sheds, etc. Is this safe?

 Grateful for any advice.


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