Kiln drying firewood
Yesterday I loaded 2 cords of mixed hardwood into the kiln, around 3pm. Then I turned on the kiln to bring up the temperature so that the dehumidifier can start its job of drawing water from the maple, birch, ash and beech wood.
The firewood’s thermal mass from being outdoors is about the same temperature. The kiln’s initial air temp record about the same, albeit a little bit warmer.
The heat is turned on and the fans as well, to circulate the warm air to rise up the overall temperature. Dehumidification will not work in a cold air environment, the coils freeze up, so that is why heat is necessary.
The next day in the morning around 10 am, the kiln is ready to start with the temp reaching 80ºF.
The dehumidifer’s compressor starts automatically to draw out moisture. Here is a short video.
It takes just about 5 minutes to fill a cup measure with 8 ounces of water.
24 hours running the kiln at this time. Time to check in on how the kiln is doing.
The dry bulb temp has increased 65ºF. The probes are starting to show a downward tend in moisture content, that’s the goal. Probably will be another 24 hours before the firewood is ready.
8 PM – The kiln is cooking right along, doing its thing. The probe average is continually dropping now. That’s the trend you want to see.
8PM – We roll through our 3rd full day now. The overall moisture content (Probe Average) continues its downward trend. I performed another time trial of 8 oz of water coming from the drip line, it took a little over 4 minutes to fill the cup. I estimate the kiln has drawn out at least 115 litres of water since it started this run of firewood.
10 PM – A few recordings during the day. The MC has slowed somewhat. I stepped into the kiln for a look. I decided the wood sample for Probe 4 was not sufficient so I moved it to another piece of wood. That’s why you will see a jump in the MC for that probe.
Today we are getting near the end of this kiln run. This reading was taken at 8am. I figure another 24 hours and it will be below 20% MC.
Today is a special day! Its February 29th after all. It only comes around every 4 years. Its also the day we have completed this cycle of kiln drying firewood. No picture of the readings this morning because when I checked, it was 19.6% probe average. That’s sufficient for firewood. So now its time to shut it all down and unload the kiln.
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Here’s a video of us unloading some of the kiln dried firewood.
Here are some stats on firewood as it relates to moisture content. A full cord is 128 cubic feet of split stacked firewood.
The average hardwood mix of the firewood we had in this batch is about 60% maple, 30% birch (mostly yellow birch) and 10% ash.
The weight of a full cord of green logs just split from logs is about 1,825 kg (about 4,000 lb).
The weight of a full cord of split stacked firewood that’s been seasoning out in the field to air dry for about 6 months weighs about 1,730 kg (about 3,800 lbs).
The weight of a full cord of split stacked firewood that’s been dried to 20% moisture content in a kiln weight about 1,430 kg (about 3,150 lbs).
The kiln removed about 300 kgs of water in one cord, that is equal to 300 liters!
300 liters is equivalent to:
- 1 standard sized bathtub, or
- 22 standard sized toilet flushes, or
- 880 bottles of beer, or
- 1,200 cups of coffee. 🙂
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