Drying wood indoors using a dehumidifyer

[Battenkiller]

I agree 100% battenkiller

How's the trout fishing by the way?

Been great this year. The water's been so high on the 'Kill I can catch 'em in by back yard... 20 miles away. %-P

That's a river I always wanted to fish. Not sure about the 'kill but high water always equals big browns where I fish

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.

 

[gerry100]

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

 

[pdxdave]

90% humidity in the basement, does not seem right.

I bet a large percentage of basements are close to 90% relative humidity, at least the unfinished damp ones that are common here. Any closed air space with moisture will tend toward 100% RH unless the temperature changes occasionally, and basements don't tend to change temperature. Caves also have very high relative humidity for the same reason.

Considering that the mean yearly RH in most regions of the U.S. is up around 70-80% RH, that is not surprising.

To test your hypothesis, I just went down to the basement to measure the RH with a sling psychrometer.

Basement floor is still wet from two major groundwater floods during Irene and Lee. Sheetrock walls feel cool to the touch, and are still very wet at the bottom where the water soaked deeply. Dehumidifier has been off for days because I am being forced out of here after 20 years and I no longer care how musty it gets down there. Walkout basement door hasn't been opened in days, and I have hardly gone down there at all in the last three weeks. Pretty damp feeling to say the least. Stinks, too.

Results?

68ºF dry bulb temp, 65ºF wet bulb temp, 3ºF wet bulb depression gives me about 86% RH. Of course, the outside air is still well above 70% RH, so there is not as much difference as you might expect. Mostly due to the temperature difference, I'd guess. Even with no activity in and out, air infiltration has prevented the air in there from rising to 100% RH, even during some of the wettest soil conditions in recent history. Interestingly, my IR gun shows the temp of the sheetrock walls is 68ºF a few feet up and 65ºF down where they are still soaking wet - same as the dry and wet bulb readings. Makes sense, eh? Says a lot about how accurate my commercial-grade IR gun is as well.

Curiously, even at a very damp 86% RH, the EMC of the wood down there is still 18% MC, and at 90% RH in the basement all wood will be at 20% EMC. Raise the RH all the way to 100% RH? According to the EMC chart, it will never rise above about 28% MC... the water content that gives the highest combustion efficiency and the MC that most wood reaches when all of the free water is gone and all of the bound water remains. A few minutes of careful thought will make all this perfectly clear as to why.

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.

 

[krex1010]

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

 

[oldspark]

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

You will have moisture condensing on everthing though.

 

[pdxdave]

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

You will have moisture condensing on everthing though.

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.

 

[maple1]

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.

 

[onetracker]

90% humidity in the basement, does not seem right.

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

 

[onetracker]

That's an interesting chart - hadn't seen that before.

From that, one could maybe expect that putting 20% MC wood into a 70°F basement would put your humidity at 90%.

Huh.

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.

 

[Battenkiller]

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

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?

Ventilation rate

The ventilation rate, for CII buildings, is normally expressed by the volumetric flowrate of outside air being introduced to the building. The typical units used are cubic feet per minute (CFM) or liters per second (L/s). The ventilation rate can also be expressed on a per person or per unit floor area basis, such as CFM/p or CFM/ft², or as air changes per hour.

For residential buildings, which mostly rely on infiltration for meeting their ventilation needs, the common ventilation rate measure is the number of times the whole interior volume of air is replaced per hour, and is called air changes per hour (I or ACH; units of 1/h). During the winter, ACH may range from 0.50 to 0.41 in a tightly insulated house to 1.11 to 1.47 in a loosely insulated house.[4]

ASHRAE now recommends ventilation rates dependent upon floor area, as a revision to the 62-2001 standard whereas the minimum ACH was 0.35, but no less than 15 CFM/person (7.1 L/s/person). As of 2003, the standards have changed to an addition of 3 CFM/100 sq. ft. (15 l/s/100 sq. m.) to the 7.5 CFM/person (3.5 L/s/person) standard.

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.

 

[krex1010]

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

You will have moisture condensing on everthing though.

Not unless your basement is cooler than the outside temperature.

 

[Battenkiller]

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.

 

[Swedishchef]

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

 

[jatoxico]

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%.

 

[Battenkiller]

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%.

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.

 

[jatoxico]

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%.

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.

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.

 

[Battenkiller]

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.
Apologies if I misread any posts.

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.

 

[woodchip]

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%.

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

 

[Swedishchef]

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

Andrew

 

[maple1]

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

 

[Battenkiller]

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

 

[woodchip]

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 ;-)

 

[My Oslo heats my home]

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 ;-)

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?

 

[Battenkiller]

I wonder if black plastic covers would be more effective?

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. ;-)

 

[My Oslo heats my home]

I wonder if black plastic covers would be more effective?

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. ;-)

Black would create more heat