How to calculate the moisture content of Firewood Logs
To make sure logs burn well, they should be quite dry (somewhere around 20% moisture) If they are too wet, they will burn slowly, coolly and with a greater smoke and tar fraction. This can be a problem with some stoves and wood burners.
You shouldn’t take your supplier’s word for the dryness of their logs (except for TurfandStuff ;-)). You should learn how to calculate this so that you can manage you logs to the best effect.
The easiest way to measure moisture content is with a moisture meter like these: Firewood Log Moisture Meters however these meters do not measure “moisture” just conductivity. They can therefore be misused or poorly calibrated. We use the meters in general use, but always use the next method for accuracy:
Method 2 is to dry pieces of wood in the oven. The drying is easy but the sample selection and preparation is important. Logs have varying moisture contents, depending on tree age, time since felling and position in the seasoning pile. The moisture content also varies from the middle of the log to the ends. You should use 3 to 5 pieces logs, of varying cross sections and Densities/”weights”. Cut each piece straight across the middle and split down the length. Discard everything except one small piece from each log.
Take the pieces, weigh them on accurate kitchen scales and note the total weight (Weight 1).
Place in a low oven (less than 100 deg c) overnight. Weigh again and note the total weight (Weight 2).
The calculation for moisture content is as follows:
Weight 1 – Weight 2 = Weight of Water
Then: Weight of Water divided by Weight 1 multiplied by 100 (Weight of Water / Weight 1 x 100)
This gives your answer as a percentage.
Here is a worked example:
Weight 1 = 1.7 Kg
Weight 2 = 1.36 Kg
Therefore 1.7-1.36=0.34
0.34/1.7x100=20%
As said elsewhere, you can experiment with moistures from 25% down to 19% and see what works best in your stove, fire or burner.
