Modern well designed wood pellet boilers offer all the advantages of a conventional gas or oil fired systems, while using an environmentally friendly and cheap fuel. There are a wide range of systems available, differing greatly in quality, safety, reliability, efficiency and price. This guide aims to explain these features allowing the buyer to make an informed decision and to select a suitable quality system for their home.
1. Safety
A well designed, high quality modern wood pellet boiler is quite safe. However as with any boiler there is a fire risk. The principle fire risk with wood pellet boilers is burn back in the fuel feed and blocking in the combustion chamber. The boiler must have features to prevent these problems occurring.
Burn back protection
There should be multiple fail safe mechanisms to prevent burn back through the fuel feed system to the fuel silo. These can include temperature sensors, air locks, fuel chutes, and heat reactive expandable foam and water sprinkler systems.
What to look out for
Ask what safety features the boiler has against burn back. Do not accept general assurances. There should be several and the supplier should be able to explain them all in detail. Ask which testing authority tested the system against fire risk. Reputable suppliers will be happy to show you the fire test certificates. Systems such as the sprinkle system and the foam are last resort features. If they are triggered they may damage the system in order to prevent fire spreading. These sorts of features should not be the sole safety feature.
Boiler control and self diagnostics
If ash or clicker build up in the combustion chamber, or the boiler fails to light, the control system needs to be able to detect this. Failure to do so may result in the boiler attempting to light while the system is blocked and the flue gases can not exit the system. A good control system can monitor what is happening in the boiler itself, detect the temperature of the flame, count the quantity of pellets that are in the combustion chamber and take action if some thing untoward occurs.
What to look out for
Ask about the capabilities of the boiler controller. Ask about its diagnostic functions. Ask how it detects if the pellets have not lit or that the flue gas is not able to exit the system. Check can the boiler record these errors to make servicing and fault finding easier.
2. Quality
A good quality boiler will last longer, be easier to use and have a higher efficiency. Quality costs money but will save you in the longer term.
Corrosion Protection
Wood combustion is corrosive. In a poorly designed the steel system will corrode quite quickly destroying the boiler. The combustion chamber must be designed to both ensure combustion has completed before the flue gases leave it and enter the heat exchange, and that the combustion chamber itself is protected against this corrosion. What to look out for The combustion chamber must be constructed from a material which does not corrode. The thickness and type of the steel in the rest of the boiler is also important. The thicker the steel and the better quality of the welding, the less it will be effected by corrosion.
Efficiency
A highly efficient boiler will burn less fuel and save you money. The SEI standard only implies an efficiency of about 83%, which is not high. Also it only refers to efficiency at rated output. In real life a boiler will not be operating at rated output and the efficiency of a poor quality system will drop significantly. A good boiler will have efficiency in excess of 90% and be able to regulate its outputs to match the heat requirement of the house, with out losing efficiency. This is sufficiently important that in some countries such as Austria, system must by law be able to reduce their output to 1/3 their rated power while maintaining rated efficiency.
What to look out for
Reputable suppliers will be able to show you test reports from independent laboratories stating efficiencies at different outputs. Ask is the system able to modulate its output. Ask how it achieves this. It is necessary that the boiler has some way to measure the combustion efficiencies, usually using a lambda probe or equivalent. Without this its efficiency can not be maintained at variable output.
3. Ease Of Use
Some boilers require regular manual cleaning, others are self cleaning. Manual cleaning generally involves scraping heat exchanges and clearing grates. For the more primitive systems it is akin to an old fashioned solid fuel stove rather then a modern heating system. Alternatively higher quality systems are fully automatic and fully self cleaning removing the need to do more then empty the ash once a month. You should understand and be happy with the cleaning requirement of the system you buy. Failure to comply with the cleaning requirement of a manual system will adversely affect efficiency and will increase the fire risk of the boiler. If you are not prepared to clean regularly you should purchase a self cleaning system.
What to look out for
Check how the system clears the grate and how it cleans the heat exchange. If it does not occur automatically ask to see the cleaning manuals. These often give a good idea of how big a chore it may be to clean. If the system does not clean itself it must be cleaned manually, so do not accept assurances that it does not need to be cleaned.
3 Sizing A boiler
operates more efficiently if it is sized correctly for the building it is heating. This means it is important to accurately calculate the heat load of the building before installing the system. It also means that you should not put in a larger system, just to make sure.
What to look out for
Ask how the installer calculates the size of the boiler required. With newer buildings it is possible to apply general rules. For older buildings, it may be necessary to carry out a quick survey and do a heat loss calculation based on the materials used, the size of the windows and the level of insulation. The installer should not just recommend a larger system just to be sure as this will just result in lower efficiency and higher heating bills. Quality Guidelines Approved 6th October 2006

Producers of Wood Pellets

Companies Producing Pellets
Balcas Enniskillen, Co Fermanagh - www.balcas.com
Dpellet Knocktopher, Co Kilkenny - www.dpellet.ie

Other suppliers/importers of Wood Pellets:
Leinster Pellets Blessington, Co Wicklow  - www.leinsterpellets.com