Tony (Fire_Man) sent me two splits of firewood he got from Dennis at the Woodstock/Hearth.com get-together. I got them the other day and immediately began to analyze them for moisture content, both with my little blue Harbor Freight meter and using the extremely accurate oven-dry method.
I got the following readings after re-splitting:
White ash - 15% MC outside, 28% MC inside. I used the Delmhorst species correction chart to determine the correction for both readings. I subtracted 3 points from the high reading (chart only goes to 24%, so I applied the maximum amount given in the table), and 1 point from the low reading. I added both readings together and divided by two to get the average MC for the entire split - 19.5% MC.
Black cherry - 13% MC outside, 15% MC inside. To correct for species, I added 1.5 points to both readings (see table below), then added them together and divided by two (as above) to get an average MC for the split of 14.5% MC.
I took each half-split and made several 1" thick cuts along the length on the bandsaw. This was done to get wood samples along the entire length of the splits. Then I chopped them into smaller chunks about 1"x1" in order for them to dry faster. Finally, I placed the small chunks from each sample into a pre-weighed plastic container and weighed them to the nearest 0.1 gram on the triple-beam balance. I subtracted the weight of the container from the total to get a starting weight for each sample:
White ash - 306.0 grams
Black cherry - 283.2 grams
I put the chunks on a dinner plate and microwaved them on high for 2 minutes, stopping every 30 seconds to loosely toss the pile. After four consecutive 30 second cycles, I placed the chunks back into the pre-weighed container and weighed them, alternating the samples each time and recording both weights as they changed. After I got three consecutive readings that were unchanged, I recorded the final weight and placed them into a pre-heated 220F oven overnight. The following morning, I weighed each sample to see if the weights had changed from the microwave drying (they hadn't).
Final weights were as follows:
White ash - 251.8 grams (water lost = 54.2 grams)
Black cherry - 243.5 grams (water lost = 39.7 grams)
I used the following formula to get the dry-basis MC of the samples:
Total water lost (grams)/final oven-dry weight (grams) x 100 = %MC dry-basis.
I determined the actual moisture content of the splits to be as follows:
White Ash - 22% MC
Black cherry - 16% MC
In both cases, my meter gave a slightly lower reading than the oven-dry method showed. The meter said the white ash was at 19.5% MC while the oven-dry method proved it to be 22% MC. The black cherry read 14.5% MC on the meter, while the actual MC was 16%.
The moisture meter measures wood using dry-basis calculations, but the wood heating industry uses another method called the "wet-basis" calculation. This is a more intuitive and useful way to visualize the water remaining in the wood as a percentage of the original weight as opposed to a percentage of the oven-dry weight. To convert the meter reading to wet-basis, just use the following formula:
Wet-basis reading = meter reading/1 + meter reading x 100
For the white ash, that is .22/1.22 = .18 x 100 = 18% MC.
For the black cherry, that is .16/1.16 = 14% MC
And that's all, folks. My thanks to Tony for spending the time and money to send this wood my way. We were both extremely curious to see exactly what the moisture content of the infamous ancient Sav-ash is, so now we know. My guess is it got down this low a long time ago and basically stayed there all these years. No sign of punk after 9 years in the stack, just good, seasoned firewood at the optimum moisture content.
I got the following readings after re-splitting:
White ash - 15% MC outside, 28% MC inside. I used the Delmhorst species correction chart to determine the correction for both readings. I subtracted 3 points from the high reading (chart only goes to 24%, so I applied the maximum amount given in the table), and 1 point from the low reading. I added both readings together and divided by two to get the average MC for the entire split - 19.5% MC.
Black cherry - 13% MC outside, 15% MC inside. To correct for species, I added 1.5 points to both readings (see table below), then added them together and divided by two (as above) to get an average MC for the split of 14.5% MC.
I took each half-split and made several 1" thick cuts along the length on the bandsaw. This was done to get wood samples along the entire length of the splits. Then I chopped them into smaller chunks about 1"x1" in order for them to dry faster. Finally, I placed the small chunks from each sample into a pre-weighed plastic container and weighed them to the nearest 0.1 gram on the triple-beam balance. I subtracted the weight of the container from the total to get a starting weight for each sample:
White ash - 306.0 grams
Black cherry - 283.2 grams
I put the chunks on a dinner plate and microwaved them on high for 2 minutes, stopping every 30 seconds to loosely toss the pile. After four consecutive 30 second cycles, I placed the chunks back into the pre-weighed container and weighed them, alternating the samples each time and recording both weights as they changed. After I got three consecutive readings that were unchanged, I recorded the final weight and placed them into a pre-heated 220F oven overnight. The following morning, I weighed each sample to see if the weights had changed from the microwave drying (they hadn't).
Final weights were as follows:
White ash - 251.8 grams (water lost = 54.2 grams)
Black cherry - 243.5 grams (water lost = 39.7 grams)
I used the following formula to get the dry-basis MC of the samples:
Total water lost (grams)/final oven-dry weight (grams) x 100 = %MC dry-basis.
I determined the actual moisture content of the splits to be as follows:
White Ash - 22% MC
Black cherry - 16% MC
In both cases, my meter gave a slightly lower reading than the oven-dry method showed. The meter said the white ash was at 19.5% MC while the oven-dry method proved it to be 22% MC. The black cherry read 14.5% MC on the meter, while the actual MC was 16%.
The moisture meter measures wood using dry-basis calculations, but the wood heating industry uses another method called the "wet-basis" calculation. This is a more intuitive and useful way to visualize the water remaining in the wood as a percentage of the original weight as opposed to a percentage of the oven-dry weight. To convert the meter reading to wet-basis, just use the following formula:
Wet-basis reading = meter reading/1 + meter reading x 100
For the white ash, that is .22/1.22 = .18 x 100 = 18% MC.
For the black cherry, that is .16/1.16 = 14% MC
And that's all, folks. My thanks to Tony for spending the time and money to send this wood my way. We were both extremely curious to see exactly what the moisture content of the infamous ancient Sav-ash is, so now we know. My guess is it got down this low a long time ago and basically stayed there all these years. No sign of punk after 9 years in the stack, just good, seasoned firewood at the optimum moisture content.