Kiln Drying Firewood

Drying firewood artificially can be an option if you have plentiful energy available and need the driest firewood possible. Kiln dried firewood is usually an extravagence when processing firewood as either natural gas, or other fuel needs to be burnt. However; if natural seasoning is for some reason not sufficient for you, for what ever reason then you could consider constructing either

• a solar kiln
• a wood fired kiln

The same general principals that apply to naturally seasoning firewood still apply, however you are aiming to accellerate the process, drying firewood much more quickly. If you are planning on seasoning your wood naturally you might find some of our drying firewood tipshelpful.

• cut wood early
• split wood immediately - smaller pieces dry much faster
• ensure good air ventilation
• ensure exposure to either solar heat or some other heat source

A Solar Kiln

Drying wood using a solar kiln may be worth considering if you live in a spot with plenty of sunshine. You basically need to construct a large greenhouse that you can stack your wood inside. On sunny days the internal air temperature can shoot up quickly and with a well designed arrangement should be capable of reaching 20 degrees centrigrade above the external air temperature.

Evaporation increases rapidly with temperature - almost doubling for every ten degrees centigrade. To make the most of this free solar heat it is also important that the air circulates well inside the kiln. Drying firewood needs low humidity air and this can be arranged by venting some of the air from the top of the kiln and allowing new air in at the base.

The most elegant solution is to arrange a solar chimney - a glass or perspex fronted chimney, insulated from the outside air, with a black painted metal surface on the inside. Locate this where the air exits the kiln, so that the sun falls on it. When it is sunny enough for the kiln to need ventilation the solar chimney will draw fresh dry air rapidly through the drying firewood. Similar ideas are used to passively air-condition solar homes.

Why might you consider a solar kiln?

Drying firewood in a solar kiln may be attractive if

• you have plenty of time and cheap/free recources to build with
• have a need to speed up firewood drying - for example cutting wood late for the coming winter heating season
• you intend to sell 'premium' kiln dried firewood
• your summers are wet, but with sunny days - you get the best out of your sunshine while still protecting the firewood from surface moisture
• you have high value dry wood products to process - for example building timbers

Kiln dried firewood can reach a substantially lower water content by % weight than logs dried in the open. If you want to dry your logs primarily in the open you could then bring them inside your solar kiln for the last few weeks before burning. Even in winter a well designed and insulated solar kiln can still reach the temperatures needed for effective drying.

A wood fired kiln

A wood fired kiln is another possible way to dry firewood rapidly, and beyond what is possible with open air seasoning. Just remember that by burning firewood you are using fuel that you could otherwise use to heat your home!

For most people owning their own wood fired kiln is an unreasonable expense - kits available online come in for around $18,000 dollars! But for businesses with high throughput of logs they can be a wise investment.

Artificially drying logs reduces the time that cut logs need to be seasoned on site for, before sale. Reduced inventory needs less storage and facilities can be substantially smaller, which in itself can be of substantial financial benefit.

Additionally kiln dried firewood can be sold for a premium over fresh cut, or even well seasoned wood dried naturally.

Building a kiln

Wood, or gas, fired kilns need to be built out of a sturdy fireproof container. Many industrial kilns have been made from converted stainless steel shipping or refrigeration containers.

What ever the structure they will also need:

• a boiler or furnace to provide the heat - if this has the option of burning scrap wood so much the better
• a fan to blast hot air into the container - hot fast moving air carries the moisture out of the container
• a control system and way of measuring moisture - either moisture content of the exiting air or in the wood itself
• Containers for quickly loading and unloading the container - "meter cube" wire trolleys work well

In an optimally run wood kiln, many cords worth of firewood can be reduced from 65-90% moisture content down to around 20% (ideal for burning) in 3 to 6 days. A resourceful tinkerer could construct a passable wood fired kiln on a limited budget, if they were willing to sacrifice speed and efficiency, but a solar kiln is probably a better option with fewer safety issues.