Domestic Wood Boilers

 

Modern wood boilers offer the warmth and comfort of traditional wood boilers but are highly efficient, clean burning and often fully automatic, saving you time and money. Wood boilers come in many different formats. Chip, pellet and log versions are available.

 

Wood chip boilers
 

These are essentially the same as wood pellet boilers. The main difference is the feeding mechanism. A stirrer is required in the store to ensure a constant supply of wood chips as they are not as uniform in terms of shape and tend to form bridges unless a mechanism is in place to prevent this.

The storage volume also needs to be larger than for chips because the energy density is less than for that of pellets. Chip boilers are generally lit automatically and continue to operate without manual intervention. Higher specification boilers are self-cleaning so you can forget the cleaning chore of traditional solid fuel heating systems.

Boiler_adjacent storage

Wood Chip Boiler with Remote Chip Storage and Feeding Mechanism
 
Wood Pellet Boilers
 
These can be considered the most popular form of domestic wood boiler as they are fully automatic in operation. Fuel handling is convenient and requires a relatively small storage volume due to the high energy density of the pellets. Storage can be adjacent to the boiler itself or in separate fuel store. In both cases a feeding mechanism (screw / auger) is used to transport the pellets from the store to the boiler. Pellet boilers are generally lit automatically and continue to operate without manual intervention. Higher spec boilers are self-cleaning so you can forget the cleaning chore of traditional solid fuel heating systems. Some pellet boilers can also operate using corn which is similar in shape and has a similar energy content.

Boiler_remote storage

Wood Pellet Boiler with Adjacent Fuel Storage
 
Wood Log Boilers
 

Modern log boilers also have very high efficiencies. These are not generally as convenient in use as the fuel logs normally need to be loaded manually. However, a certain amount of storage in an integral chamber limits the frequency with which reloading of logs is required. Log systems work best where heat is required over longer periods of time as the boilers are not as suited to frequent start up and shut down sequences. Some systems use a large hot water storage tank or buffer in order that the boiler can be lit once, the heat stored and subsequently used over a number of days, before the boiler needs to be restarted. Log boilers can be an advantage where you have your own supply of wood as the running costs can be very low while providing you with a degree of self-sufficiency.

Gasification boilers maximise fuel efficiency to achieve, as close as possible, complete combustion of any fuel. Wood log gasification boilers are now commonly available in the Irish marketplace.

Log boiler

Log Boiler
 
General Wood Boiler Information
 

Ash

With all types of wood boiler, some ash is produced (usually less than 1% of fuel input). The ash pan needs to be emptied bi-weekly, or less frequently, depending on service. Ash can be disposed of in the garden and is beneficial to plant growth.

Fuel / Storage

Pellets can be purchased in bagged or bulk form. For bulk purchases, a dry covered storage area is required. Generally bulk prices are more competitive than those for bags. Wood chips are generally sourced locally. It is important that the fuel used (quality, size, moisture content) is suitable for the appliance; your supplier will provide you with these details. For pellets, bulk delivery can be arranged to your home where the delivery truck uses a blower to deliver the fuel into your shed, storage room or outdoor silo. 2 tonnes of pellets will deliver the same amount of heat as 1000 litres of heating oil.

Operation and Efficiency

The latest wood boilers offer remote control and monitoring, accessible by mobile phone. It is important that there is adequate ventilation and that a clean air source is supplied to the boiler, as the combustion process uses oxygen (in the same way as any fuel fired appliance). For correct operation and maximum efficiency a hot water buffer store should be supplied with the system.

High efficiency makes economic sense
Wood boilers use the latest technology to control the amount of fuel and air released to the burner. Typical costs of boiler and installation range from €10,000 for 15kW home boiler to a €20,000 for a 100kW boiler for a large building. The lower cost of the fuel competes well with similar oil systems.

Operation and maintenance
Wood boilers operate just like a conventional central heating system and work in conjunction with radiators or under-floor heating. You can control the heating system and regulate the temperature from a panel control. Most reputable boiler suppliers offer service contracts to ensure an optimum operation and long life of the boiler. Many boilers have an automatic system alarm that is sent to a service engineer via SMS messaging on a mobile phone. Quality boiler suppliers report very low failure rates and most problems are solved within minutes, remotely without callout.

Your checklist for selecting a wood boiler

  • Efficiency of 85% or higher
  • CO2 Emissions less than 200 mg/m3
  • After sales service contract
  • Automatic cleaning
  • Good quality burn back protection

Planning for a wood boiler

  • Fuel Storage for 3-4 tonne of wood pellets per year (allow up to 50% more for wood chips due to lower energy density)
  • Pellet Storage space of 2 X 3m floor area & 2.25m height (for domestic 15kW boiler)
  • Boiler room size of 2m X 2m X 2.5m height
  • Select a trained professional installer & supplier
 
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