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Drying wood indoors using a dehumidifyer

Post in 'The Wood Shed' started by MOHAWK1, Sep 26, 2011.

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  1. Battenkiller

    Battenkiller Minister of Fire

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    Oh, yeah, and the Battenkill is big brown water without a doubt. The problem this year has been in finding them in the surrounding fields... literally.

    Send me a PM. Always glad to take people out on the 'Kill, be glad to fish with you if you ever get in my area.

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  2. gerry100

    gerry100 Minister of Fire

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    My basement is too damp in the non burning months when I use AC for comfort

    During the burn season it gets so dry I like most others put a pan of water on the stove top

    Could putting wet splits in the stove room help with the dryness and season wood

    may be practical with some setup
  3. pdxdave

    pdxdave Member

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    Seasoning is sped up by drier air, but by no means is there a limit imposed at the RH% of the air. Air has a higher moisture capacity than wood at the same pressure/temp, so there is a natural transfer of moisture from wood to air as the cells break down inside the wood. Lower RH accelerates the 'death' of the wood cells and this transfer.

    100% RH means it is raining. So if you hit 100% RH in your basement, you've got alot more issues than just some dripping wet wood.
  4. krex1010

    krex1010 Minister of Fire

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    It can very easily be 100% rh in your basement and not be precipitating inside your house.
  5. oldspark

    oldspark Guest

    You will have moisture condensing on everthing though.
  6. pdxdave

    pdxdave Member

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    Yup.
    I have actually experienced indoor rain in a hot, humid part of Mexico in mid-July. The A/C was running in the room next to me, and as the cold air leaked out from the top of the adjacent doorway, it cause the 95% RH air to condense, and little drops of 'rain' were landing on me.
  7. maple1

    maple1 Minister of Fire

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    That is likely due as much to the cold air leak than the rh level.

    I have basement rain too once in a while - but that is condensation off an uninsulated cold water pipe feeding the washer a couple of loads in. Happens in all kinds of weather/rh levels.

    I think you could see 100% rh in a basement without rain happening - mine gets over 90 at times and it only feels a little stuffy.
  8. onetracker

    onetracker Minister of Fire

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    if i don't dehumidify my basement it shoots up to 90% in summer.
  9. onetracker

    onetracker Minister of Fire

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    3 years ago i must have brought in some damp wood cuz there was water DRIPPING from the ceiling in my shop (its structural concrete) i thought that maybe it was soaking in from outside but it was the firewood causing it. i think that load was probably only seasoned for a few months.
  10. Battenkiller

    Battenkiller Minister of Fire

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    I put up to 1 1/2 cord of unseasoned wood in my basement at a time and it only has a very minimal effect, and it only lasts for a few days. I documented this all extremely carefully last year and presented the data here on Hearth.com. I used a weather-grade sling psychrometer that has two thermometers in it. They are attached to a carrier that allows them to be swung rapidly through he air. One of them (the "wet bulb") has the mercury bulb encapsulated with a wick, which is dunked into distilled water, while the other one (the "dry bulb") sits right beside it. When the device is spun in the air, the distilled water in the wick of the wet bulb evaporates, causing the temperature to drop through evaporative cooling. The difference between the two thermometers is recorded and then the relative humidity of the air is determined using something called a psychometric table. This method is extremely accurate compared to the Home Depot dial-type humidity indicators most folks have.

    OK... what did I find?

    Several hours from the time I'd first bring in the wood, the humidity would start to rise. At the end of about 24 hours, the RH in the basement would rise from the low 20% range up to about 40% RH. That is just about perfect for inside winter living conditions. On the second day, however, the RH would drop down into the upper 30% range, them into the high 20% range after about five days. The wood itself was drying rapidly, losing hundred of pounds of water in a very short period of time. This was confirmed by weighing various splits and recording their weight changes. I kept one split and recorded all of the weight changes through the entire season. It went from about an initial 57% MC all the way down to about 20% MC within three weeks. Multiply that by a few thousand splits over the course of the winter and you can get an idea of how much water was being released into the home.

    Where did all the water go? It was definitely evaporating out of the wood and into the surrounding air. Why didn't it raise the humidity level in my home? Air exchange, as I mentioned before. How much?

    So, even in a very tight home, the air inside is being completely replaced by outside air every other hour! Knowing this, it is hard to have faith in a pan of water making a big difference, never mind a few splits of wood. HVAC experts say that the average tight home of 2000 sq.ft. needs about 5 gallons of water added every day in order to maintain a 40% RH level. A leaky home will need twice that amount. My leaky home would need about 2100 gallons of water in a seven-month heating season in order to achieve that goal. Five full cord of dense hardwood dried down from green to 20% MC would only add about 1/3 of that amount.

    Now, there are some who claim to get satisfactory results by drying laundry by the stove. They may think they feel better, but trust me, they would never fool my weather-grade instrumentation.
  11. krex1010

    krex1010 Minister of Fire

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    Not unless your basement is cooler than the outside temperature.
  12. Battenkiller

    Battenkiller Minister of Fire

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    It's all about dew point. If the temperature of the basement surfaces is lower than the dew point of the contained air, moisture (dew) will collect on these surfaces. If not, then it won't. Simple as that.

    OK... not so simple. Dew will have a harder time forming on porous surfaces and poor thermal conductors like wood, but it will definitely form on exposed pipes and come down like rain.
  13. Swedishchef

    Swedishchef Minister of Fire

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    Holy crap, what a post.
    BK : Are you an engineer? You sound like one! Lots of my buddies are P.Eng and sound like you! I agree with everything you have said.

    To get back to the OP, I think that a nice big fan, some heat in the basement and a DEhumidifier will certainly accelerate the drying process. I don't know where you live, but where I live we don't get wind 24/7. A couple of commercial fans (that run at about 100 watts a piece) and a dehumidifier will do a better job than mother nature can: you can control the climate inside but not so much outside. However, will it dry the wood quick enough for this winter? Will it be cost effective? The only way to find out is to try it.

    Andrew
  14. jatoxico

    jatoxico Minister of Fire

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    I think a major point of that is being missed is that the MC of wood is calculated on a weight basis eg. 30g water per 100g of wood = 30% MC.

    Relative humidity is not calculated this way. From the attached chart notice that at 20 C (around 70 F) the actual amount of water on a g basis is only 8g/1000g air at 50% Rel Humidity and 15g/1000g at 100%.

    Attached Files:

  15. Battenkiller

    Battenkiller Minister of Fire

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    Yes, the RH of air is temperature dependent while the MC of wood is not. Heating up a split with 50% MC will not change the amount of water it can hold. I don't see how this fact changes anything. Water molecules will leave the surface of the wood at a faster rate when the RH is low than when it is high. That's where the dehumidifier comes in.

    Since the only way water can leave the split is directly from the surface into the air, water inside the split must migrate to the surface across a diffusion gradient that is established by the water leaving at the surface. Therefore, the faster the water leaves the surface (i.e. the lower the RH), the steeper the gradient becomes, and the faster water molecules will migrate out of the inner portions of the split, and the faster the entire split will dry. That's why I said earlier that RH is what drives the entire process, not temperature per se.

    Heating up the air in the basement will lower the RH and allow water to leave the wood surface faster. That's why this process works so much better in the dead of winter. The frigid outside air contains very little water even at a high RH. As that air infiltrates into the heated spaces, the RH drops like a stone and rapid drying begins. In a naturally ventilated system like a home, the moisture that leaves the wood soon exits the living space as new dry air moves in from the outside.

    With a dehumidifier, the water is removed from the air by the cold condensation coils of the dehumidifier (which are well below the dew point) and drips into a container to be removed, or is drained away continuously through a hose or pipe of some sort. There is no need to continually introduce fresh air into the storage place because the air is continually being dried by the condensation process itself.

    FWIW their are two principle methods for calculating the MC in wood. The one you mentioned - wet-basis - is the most intuitive way, but it is not the way MC is expressed by wood technologists. They use a method of calculation called dry-basis. It is the weight of the water divided by the dry weight of the wood fibers themselves. Wood that is 30% water by weight is 70% dry wood fiber by weight. 30÷70 = .429 X 100 = 42.9% MC dry-basis. It is crucial to understand this point if you are using a moisture meter to judge the readiness of your wood. After all, fresh-cut white ash that might read 42.9% MC on a meter (dry-basis) is durn near ready to burn just as it is (and some folks do burn fresh-cut ash with success), whereas wood that might be 42.9% MC wet-basis like red oak (70% MC dry-basis) will hardly ignite.
  16. jatoxico

    jatoxico Minister of Fire

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    My only point was; from reading the thread there seemed to be a question among some as to how wood could apparently become drier than the prevaling RH. eg if RH is 50% how can wood ever get less than 50%? I was simply pointing out than RH and MC are not expressed in equivalent scales of measurement. So wood of 40% MC will dry even in conditions of high humidity and cool temp although the process will, of course, be slower than if temp is high w/ low humidity. It is also why you can put "dry" wood in your basement and still raise RH.
    Apologies if I misread any posts.
  17. Battenkiller

    Battenkiller Minister of Fire

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    No need to apologize. I was just going on in my usual verbose way, trying to help clarify the way wood dries. I've gone through these concepts plenty here in the last few years, but there is a new crop of burners every year. Only trying to help educate them, as I am sure you are doing yourself.
  18. woodchip

    woodchip Minister of Fire

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    That was what I was trying to get at on the previous page, but probably not very well........ ;-)
  19. Swedishchef

    Swedishchef Minister of Fire

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    We should all have kilns inside out houses! I wonder if anybody does...

    Andrew
  20. maple1

    maple1 Minister of Fire

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    I don't think I've seen any out houses that would hold more than a couple of armloads though.
  21. Battenkiller

    Battenkiller Minister of Fire

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    I'd try that, but I don't even have an out house. Put a flusher in back in '03.
  22. woodchip

    woodchip Minister of Fire

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    Our greenhouses now have 2 cords in them spread out, we are having an unusually warm spell (120f inside them today with the doors open) and a nice drying breeze.

    No power being used to dry the wood, just a simple solar kiln that's empty now the tomatoes are finished.

    Long may this continue, drying wood and not burning it ;-)
  23. My Oslo heats my home

    My Oslo heats my home Minister of Fire

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    I have noticed the same effect on the tops of my stacks in the backyard, the clear plastic covers the row (tops) and the top 8-10 inches is much dryer than the lower uncovered sections of the stack. I wonder if black plastic covers would be more effective?
  24. Battenkiller

    Battenkiller Minister of Fire

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    Just curious... why do you think black would be better? I believe clear plastic would be better because you want the sunlight to go through the plastic to warm up the inside. Just like a car on a sunny day... or a greenhouse. ;-)
  25. My Oslo heats my home

    My Oslo heats my home Minister of Fire

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    Black would create more heat
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