Fire wood and wood burners

The most common type of heating in a New Zealand home is a woodburner. One of the reasons for the popularity of the wood burner is its sheer power, which typically ranges from 10-20 kW. Compare this for example to a heat pump which is typically less than 6 kW.

Once lit and the wood is hot enough, the volatiles (combustible creosotes and resins) evaporate out of the timber and are burnt as gases. If these gases are not burnt completely the result is smoke. The evaporation of the volatiles turns the wood to charcoal, which then burns easily and cleanly, and produces most of the heat.

To burn as cleanly as possible, the fire needs to be as hot as possible and with the right amount of air to support the combustion. More...

Modern woodburners burn efficiently because the firebox is lined with firebrick material, making a hotter fire, and the air intake is designed to give the most complete combustion possible. The resulting efficiency (conversion of the fuel energy into heat in the room) is around 60 to 70 percent (compared to the traditional open fire of 15 to 20 percent).

Whether you burn wood in a fireplace, stove or furnace, good quality firewood is the key to convenience, efficiency and safety. Wet wood and pieces that are not the right size and shape for your wood burner can be frustrating, burn inefficiently and deposit creosote that can fuel a dangerous chimney fire. Good planning, seasoning and storage of the firewood supply are essential to successful wood burning.

Unfortunately, there are no standards for firewood and that means that there is a large variation in quality. This applies especially to moisture content. Fire wood burns best when the moisture content is less than 20% (wet basis). To dry wood naturally to this level would require leaving the wood to dry under cover for up to 2 years.

Tips on buying good firewood:

• Ask friends and neighbours who burn wood for recommendations on reliable suppliers.
• Shop around and select the dealer who seems most reliable and comes with the best recommendations.
• When delivered, check your firewood for overall peice size. 10cm dia is preferable.
  
• Look for wood that is clean. Sand and mud on firewood makes it less desirable. 
• Do not buy randomly piled wood. Only purchase by the thrown m³.
• Check the delivery vehicle for MAPSS(measurement and product safety service) approval.
• If possible, get the wood in spring and stack it in your own yard so you can control the seasoning process.

More...

Firewood Retailers:

• Yellow pages
• City Firewood - Christchurch
• Wholesale Manuka Supplies - Wellington
• Bark 'n' Firewood Bin - Auckland
• Ernslaw Bio-Energy - Central Otago