The boilers expected lifetime is critical. Not only is it frustrating if your boilers break down, but the RHI is paid on the actual boiler, not the installation. So if your boiler needs replacing in 10 years, that’s the end of your RHI payments.
Fuel efficiency is frequently overlooked, the brochure may well state it is 94% efficient, but so did a German car manufacturer’s! The key to efficiency is having the information from sensor, the controller to compute that information and then the knowledge and skill from years of experience in how fire really works. Fire is a complex chemical reaction which is affected by so many factors; wood moisture, chip size, wood density, primary air under the fire, secondary air mixed with the combustion gasses. By measuring not just the residual oxygen content, but the temperature of the combustion chamber, the flue gas temperature, the negative pressure in the burn chamber then a well designed controller can really get the very best out of the fuel being burnt.
Information on the boilers performance. Is it enough just to believe the boiler is performing properly. The best boilers on the market constantly tell you what they are doing. They are continuously adjusting their settings to match fuel input with heat demand. If you can’t see what it is doing, then how sure are you until it’s too late. If the boiler does stop, why did it stop. The best boilers will tell you exactly what has happened. Is the ash auger blocked, or then oxygen level too high? How do you know they have a problem? Internet connected boilers will report issues as soon as they happen, so you know before you get cold.
The boilers reliability is really important, there is a huge difference in the quality of not just the components that are used in biomass boilers, but also in the thought and engineering that has gone into the design. A long pedigree in boiler manufacture is critical. Only through experience will you truly see what actually works when you heat it to 900 degrees and then cool it back down 3 times a day for 20 years. It’s not what designers use, but how they are integrated in the package that matters.
Ease of maintenance
If a boiler isn’t easy to look after, it won’t get done. The excitement of a new boiler soon dies away when you have to scrape ash away on a weekly bassis, or you have to climb on top to clean the heat exchanger tubes every month to keep the boiler running. There is a huge range of automation available from manual emptying of burn chambers every day through to completely automated cleaning and ash removal to well designed ash bins.
A boiler is no good when it is broken down. The reality is that biomass boilers are mechanical bits of equipment and from time to time things do go wrong. When this happens you either have to fix it yourself, or find someone else who can do it for you. The quality of advice available is critical both from the install partner and from the manufacturer of the biomass boiler