Kiln Dry Firewood

Kiln dried firewood has been seasoned ‘unnaturally’ by placing it in a kiln instead of drying it outside in the open air.


 Is Kiln dry firewood a good option?

 

Kiln dried firewood has been seasoned ‘unnaturally’ by placing it in a kiln instead of drying it outside in the open air.
Why is Kiln dry firewood a good option?
There are a good reasons to use firewood which has been dried in a kiln, this makes it a preferred option for some people. Green wood (when a tree is initially cut down) has very high moisture content and doesn’t burn efficiently. Green wood produces a lot of smoke and ‘bad air’ and by products which is bad for the environment.

 

Because of this firewood must be seasoned which allows the wood to dry – therefore burn more efficiently. The ‘normal’ method of drying firewood is to leave it outside to season, depending on the type of wood this can take between 6 months and 2 years. To increase the speed of natural seasoning wood can be kept inside (such as in a wood shed) or under covers, this reduces the amount of direct moisture such as rain and also reduces moisture absorption from the air.

How do Kilns work?

 

The firewood is placed inside the kilns which are basically large ovens that then bake the wood and water is forced out. The time period to kiln dry firewood depends on the heat used but can be undertaken over a number of weeks. Which means companies or individuals can take green wood and have it in ready to burn in a very short period of time. Plus it will be consistently dry throughout the wood – unlike naturally seasoned wood which can be quite varied – with wood on the outside of the stack being well seasoned and inside still relatively green.

Is Kiln dry firewood a good option?


There is energy required to kiln dry the wood and therefore the cost is generally somewhat higher than naturally seasoned wood. However, you can be 100% sure that the wood is well dried with a very low moisture content which means it will produce more heat per kg. It is also a good option if you have left it late to buy your firewood and find yourself buying wood in the middle of winter. This is often a time when firewood suppliers are running low on well-seasoned wood and there is a higher chance of you being sold wood that has high moisture content and therefore will produce a lot less heat.

There are a number of firewood suppliers in New Zealand that produce kiln dried firewood, however it is not as prevalent as naturally seasoned wood. Firewood NZ’s recommendation is to buy your firewood well in advance of when you need to use it, keep it covered and in an area where air can move through the stacked wood. Therefore you can be sure by the time winter rolls around and you need to use the wood it is well seasoned naturally and has a low moisture content – thus saving on the premium required on kiln dried firewood.

 

FirewoodNZ Avg. Cost/m3NZ Avg. Cost/cordHeat Output kWh/cu.mHeat output kWh/3.62cu.mPrice per kW heat producedBurn timeTypeFirewoodNZ rating
Poplar Firewood $100 $260 1,200 4,344 $0.08 Fast burning Soft hardwood C-
Eucalyptus Firewood $140 $350 1,270 4,597 $0.11 Fast burning Hardwood A-
Pine Firewood $80 $240 1,091 3,949 $0.07 Fast burning Soft wood B-
Macrocarpa Firewood $130 $320 1,150 4,163 $0.11 Slow burning Medium density wood B+
Gum Firewood $140 $370 1,270 4,597 $0.11 Slow burning Hardwood A-
Manuka Firewood $180 $500 1,860 6,733 $0.10 Slow burning Very Hardwood A
Tea Tree Firewood $180 $500 1,860 6,733 $0.10 Slow burning Very Hardwood A
Hotmix Firewood $100 $260 1,150 4,163 $0.09 Fast/Mid burning Soft/medium wood B

 These values are based on an average moisture content of 20%. Remember that firewood is sold as a "thrown meaure" so will reduce by one-third in volume when it is stacked.

 

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