Desired Moisture Content Of Firewood

windslamOctober 2, 2011

Anyone have some insight on the best moisture content of firewood used in an airtight wood stove that is used 24/7 to minimize creosote build up?

I've been burning hard wood in an air tight wood stove for some years now and although I have searched the web extensively I cannot seem to find a consistent standard for firewood moisture content. I see ranges from 25% down to 7%. I use several different meters to measure the content of the fire wood and they all are close within 2 or 3 percent. I'm hoping someone knows or has a source that can give good accurate information on what is the safest and least trouble free standards for moisture content in wood being used for wood stoves.

I try to get mine down to zero readings on the meters for Cherry, Red Oak, Apple, Maple and Black Locust. After I put it into a well protected wood shed, I notice the moisture meter might read 7-10% a few weeks later. I can take another reading a month later and it will show only 2%.

I burn mine pretty much 24/7 and sweep the chimney and stove pipe once a month to be sure I don't have creosote build up. I also use the Rutland creosote remover as an extra safeguard. My heart sinks when I throw some logs in for the night and hear a slight hiss. I know I'll have creosote if I close the air intake for an all night burn. Most times this is from under the black locust bark. I've started removing the bark from the black locust but this years supply shows a reading of 10% where the bark was and 0-7% on the rest of the log.

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20% plus or minus moisture content is pretty close to the ideal. This is what kiln dried firewood aims for.

I would really have to question the accuracy of a 0% reading on a moisture meter. Wood with no water content at all would be a powder which would be consumed in minutes. Even the 7% readings are more than a little suspect - this is around the standard for lumber intended for furniture making. Unless you live in the desert, such a low moisture content would be not be achievable with air drying.

If you're getting a minimal amount of creosote when you have your chimney cleaned - say a gallon or so - and it's the loose flakey type rather than the shiny black coal-like type, all is well. Keep in mind, though, that when the air is cut off completely, or as completely as a closed air control allows, you're causing the wood in the stove to first be reduced to charcoal before it ignites. Creosote formation is almost inevitable in this process. Stuffing the stove full of wood, then shutting down the air completely before going to bed has never struck me as a good practice. Much better to have a good bed of coals at shut down time. They will last until morning and provide a quick start to the next day's fire.

For much more information about this subject, check out

    Bookmark   October 3, 2011 at 5:23AM
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Great info Mainegrower, thank you for your response!
I cover the wood with clear plastic every evening or when it is going to rain and uncover it every morning to let the sun beat on it. Sometimes I might leave it on all day if I don't get a chance to get out there and uncover the stacks. When I measure the top row on the pile, I get the 0 percent readings and further down in the pile I get higher readings of 7-10 percent or so. I imagine the outer layer might show 0 because the sun dries it and that explains why I get the higher readings after putting it into the shed.

I never really close the stove off completely. I put a few logs in and just close it down enough not to have a really hot fire but just enough for a slower burn to continue to warm all night and not to have any back puffing.

Your information also helped me figure out why, when I tested a few studs in the garage with the meter I got 7-10 percent readings. I know the studs were dry but thought I would get readings of 0. As for the creosote, I get exactly what you describe, about a gallon paint can worth of soot and creosote out of the 25 foot chimney when cleaning it. I of course might get more soot if I've burned poplar. It gives a good fire but burns quick and leaves a lot of ash and soot. I like the black locust best but the cherry and apple smell good outside when burning.

What's your take on the Rutland creosote remover granules? They seem to put a brownish coating on the creosote which I assume is to retard the volatility a chimney fire? I have my chimney lined with the sort of spiraled stainless steel liner which seems to do a good job. Most of the creosote gets into the spiraled part which I think helps prevent chimney fires if kept cleaned. Do you have knowledge on that also?

    Bookmark   October 3, 2011 at 11:33AM
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Anti-creosote products whether sprays or granules are a bit controversial. Good ones - and Rutland is a very reliable company - do work. They don't really prevent creosote but do cause it to turn into an easily removed powder.

I've been heating with wood for more than 30 years and have never used anti-creosote products. Doesn't sound like you need to, either. Good dry wood and a modern EPA stove properly operated really removes most of the chimney fire danger.

Your moisture meters, btw, seem to be reading only the outermost portion of the firewood. The readings for the garage studs seem about right, but the readings seem very inaccurate for things with a greater cross section than 2x4". Sun and wind help, but keep in mind that it's not easy to air dry firewood to a moisture content significantly below the ambient humidity.

    Bookmark   October 4, 2011 at 5:34AM
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Thanks Mainegrower, your info is a big help. I haven't been pushing the probes into the wood real hard because I suspect it would weaken them. However, today I did push the probes in as far as I could and I get average readings of the firewood of around 10-15 percent. I've obviously only been measuring the outside layer exposed to the sun, which gave me such low readings before. Still, it's good to know 20 percent is the average I should be looking for to prevent burning wet wood.

    Bookmark   October 5, 2011 at 8:34PM
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why cannot we get some knowledgable pros to post some serious answers, instead of frustrated home owners like myself, asking questions instead of providing answers ?


    Bookmark   March 18, 2014 at 10:11AM
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What are you looking for?

    Bookmark   March 19, 2014 at 8:34AM
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I won't call myself an expert by any stretch, but I have been heating my house with wood for over ten years now. The measurement of moisture in fire wood should be taken along the flat side of a freshly split piece, not from the outside of the log or the ends. Most of the time, my firewood will be between 18 and 20 on my meter when I burn it. Keep in mind also that most of what is sold as seasoned oak is anything but - if you're lucky, it might have a year's worth of seasoning. Hardwoods like oak and locust will take about three years to dry sufficiently to burn well. Less dense woods will 'season' a lot faster, but if you want the benefit of the harder woods like oak, be prepared to maintain a three year supply to give the oak enough time to season properly.

    Bookmark   March 27, 2014 at 8:08PM
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