# Greenhouse for drying wood?



## Notomo (Apr 21, 2015)

Just wondering if you could use a greenhouse for drying wood just with more venting/exhaust. Just thinking if I am going to build a drying structure it would be nice if it was dual use so if I was not drying wood it could still be utilized.


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## johnny5ny (Apr 21, 2015)

Negative.
Good air flow is the most important aspect of the drying process.


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## Notomo (Apr 21, 2015)

johnny5ny said:


> Negative.
> Good air flow is the most important aspect of the drying process.


Don't get why you say negative, it would be easy to make a greenhouse with good ventilation just add vent fans and intake vents. I mean heck this solar kiln plan looks a lot like a greenhouse http://pubs.ext.vt.edu/420/420-030/420-030_pdf.pdf I have not read it yet but I plan to. Just wondering if anyone has converted a greenhouse or made a dual use already. I don't see why it can't be done. But if it for sure can't I would like to know.


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## Sharpie (Apr 21, 2015)

Hi i am Ron Sharpe i put up a green house kiln last summer and it works great. You can call me and i can tell you all about it and tell you what i did. 519 852 7061 I live in cold canada and i can Finnish hard wood to 6% in 4 weeks.


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## _RJ_ (Apr 21, 2015)

To be fair you said greenhouse first. Then asked why a solar kiln wouldn't work. Most people don't use greenhouse and solar kiln interchangeably. The greenhouses I see aren't well ventilated. I know mine isn't. But yes, solar kilns work great. I know an old timer that uses one. If you can build the structure to be dual use go for it.

Edit: left out a sentence.


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## Notomo (Apr 21, 2015)

_RJ_ said:


> To be fair you said greenhouse first. Then asked why a solar kiln wouldn't work. Most people don't use greenhouse and solar kiln interchangeably. The greenhouses I see aren't well ventilated. I know mine isn't. But yes, solar kilns work great. I know an old timer that uses one. If you can build the structure to be dual use go for it.
> 
> Edit: left out a sentence.


But I did say with more venting. Greenhouses around here are normally the hoop style and during the hotter season they roll up the sides to let more air flow through otherwise they get to hot, I read that article I posted a link to above, it sounds like in some areas instead of just doing the roof with the clear plastic they slope the whole wall/roof with clear. I think that is what I would do as well for a greenhouse/kiln plenty of sun for plants when I want to grow plants and I can just cover part of the clear to let in less sun when I am drying wood. In either case it will need good venting. Without the fans running it said the internal temp can get above 200 degrees which can melt the fan blades thus you need to always run the fans when there is sun.

My main concern was if the sun would do anything harmful to the drying wood I suppose though you can just put old wood on top or wherever sun would hit to protect the wood you want to keep un sun bleached. I think I will try and do like a half hoop with a back wall with fans and baffles it will be a lot cheaper than their plan but otherwise fairly similar in design. I just took apart our old full hoop greenhouse and was planning to re build it new "turns out it was a bit on the neighbor's property". If it works out I will post about it. If it does not work to dry wood at least I can still use it as a greenhouse .


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## BobL (Apr 22, 2015)

Sharpie said:


> Hi i am Ron Sharpe i put up a green house kiln last summer and it works great. You can call me and i can tell you all about it and tell you what i did. 519 852 7061 I live in cold canada and i can Finnish hard wood to 6% in 4 weeks.



That's pretty good.
I'd like to see some picture of your kiln if you could post them.


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## M.R. (Apr 22, 2015)

Don't think BobL is the only one. ;-)
Have you also done a search on the Foresty
Forum under ' Drying and Processing ' ? 
.
The lightning struck pine pictured.. had been dead 2 years
Took 3 cleanings of the bar & chain/ clutch to get 
the butt end off...pure pitch seemed like.

http://www.*****************/board/index.php/board,8.0.html


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## Notomo (Apr 23, 2015)

Did you guys look at that link I posted, it says it dries a load of wood in a month as well they have a pic of it as well "Virginia Tech Solar Kiln Design The solar kiln described in this publication was designed, constructed, and tested at Virginia Tech. This design is based on 25 years of research and development on the solar drying of lumber in the United States and foreign countries. Previous versions of this kiln were designed to hold up to 2,000 board feet1 of lumber. Plans for the older and larger kiln are available for download at www. woodscience.vt.edu/about/extension/vtsolar_kiln.asp. The version described here holds 750 to 1,000 board feet of lumber. The kiln dries a load of lumber in approximately one month of moderately sunny weather at its location in Blacksburg, Va." here is the link again http://pubs.ext.vt.edu/420/420-030/420-030_pdf.pdf There is a ton of good info in it.

Here is a pic I grabbed from the pdf


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## kimosawboy (Apr 23, 2015)

Notomo
You have to take all the info in the Virginia tech article as a rough guide and not a bible as you seem to be doing. Also dont forget that the information is ten or more years old,somewhat outdated, they would not be using tar anymore to coat the ends and they would probably be using twinwall polycarbonate instead of PVC panels.. for example.
As for your idea of making a common green house/kiln , you could easily do it but neither will work well. Either do one or the other. You also have to take into account the times you want to use your kiln vs. greenhouse. Do you want to be milling wood in the middle of winter so you can use your greenhouse in the early spring?
Just some things for you to ponder.

Regards
G Vavra


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## Notomo (Apr 23, 2015)

kimosawboy said:


> Notomo
> You have to take all the info in the Virginia tech article as a rough guide and not a bible as you seem to be doing. Also dont forget that the information is ten or more years old,somewhat outdated, they would not be using tar anymore to coat the ends and they would probably be using twinwall polycarbonate instead of PVC panels.. for example.
> As for your idea of making a common green house/kiln , you could easily do it but neither will work well. Either do one or the other. You also have to take into account the times you want to use your kiln vs. greenhouse. Do you want to be milling wood in the middle of winter so you can use your greenhouse in the early spring?
> Just some things for you to ponder.
> ...



I am not taking it as bible not even close plus I am agnostic so even if it was the bible I would not care. I just thought there was a lot of good info that was actually tested not just hearsay. Mine will differ from theres quite a lot, mainly because I don't want to spend that much and I think they could have done a few things differently to save money. Do you know of a similar guide that is newer? I would like to look at it, I have not researched it that much yet. I will do a lot more research right before I start building something this was just a pdf I stumbled on while researching other milling stuff and I thought it had a lot of good info.


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## farmer steve (Apr 23, 2015)

since i have a greenhouse i have thought about using it for drying firewood. lumber would be even easier .temps here in the GH in summer exceed 120*with the exhaust fan running. it's probably 75-80* today and its 45*outside and cloudy. properly stripped lumber should be able to dry to a decent MC %. my GH cost me about $7K 7 years ago. 21'x72'


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## BobL (Apr 23, 2015)

farmer steve said:


> since i have a greenhouse i have thought about using it for drying firewood. lumber would be even easier .temps here in the GH in summer exceed 120*with the exhaust fan running. it's probably 75-80* today and its 45*outside and cloudy. properly stripped lumber should be able to dry to a decent MC %. my GH cost me about $7K 7 years ago. 21'x72'



If the timber is well stacked and has sufficient air moving around and through it, then temperature is not that important. As Sharpie says above he's living in cold Canada and he can dry his wood easily.

My reading of the plans and science behind solar kilns is that exhaust fans are also not that important. 

In the Virginia tech model described in the link above, no exhaust fans are used and it just relies on passive venting ,with cooler air coming in from down low and some vents up near the top of the roof. There just needs to be enough air being removed to get rid of excess moisture.

What most home made solar kilns ignore is internal air turn over to help even out the temperatures inside the kiln. Failure to do this can lead to mould growth on timber if too much wet timber is put inside a kiln, and too rapid a drying for the timber is placed higher up in the kiln.

The reading I have done suggested that optimum drying requires about 1W of fan power (running 24/7) per cubic foot of kiln drying volume .
So a 20 x 10 x 8 ft kiln will need about 1.5kW of internal fan power.
I have a sea container of that size which I started to set up as a solar kiln but 1.5kW of power for 4 weeks would cost me $250 (yes we have very expensive power) which I was not prepared to pay for.
Solar powered fans would need battery back up because the internal turning over of the air is needed at night times to help the wood relax from the drying stresses of the day.

A much smaller kiln that can hold a smaller quantity makes more sense because most DIY are not going to fill a sea container worth of timber in one go.
The VT solar kiln is much smaller and has a drying volume of about 250 cut, which is why 3 small 80W window fans can do the business.


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## Cody Colston (Apr 23, 2015)

There are some considerations to making a solar kiln work. One is air flow. You need approximately 150 fpm circulating through the lumber stack for efficient drying. That means fan(s). Just venting and allowing for inflow will not provide enough air flow. The lumber will not dry "bright" and will likely mildew or mold, depending on the species.
To calculate the size of fan needed (in cfm), multiply the number of sticker layers by the length in feet of the wood stack times the thickness in feet of the stickers. My solar kiln is sized for 300 bf capacity and I use a single 1400 cfm fan on a timer to provide air flow.

Also, you need about 10 sq ft of solar collector for every 100 bf of lumber. Too much and you risk drying the lumber too quickly, with the inherent degrade that could ruin the entire stack. Too little, and the lumber will not dry quickly enough with, again, mold mildew and staining the result. You can partially cover the solar collectors to reduce the sq ftg if it is too much but not much can be done if it is too little.

While lumber will dry in low heat (as noted by the Canadian), higher heat will speed up the process. Increase the heat without adding moisture and you lower the relative humidity. Heat, air flow and relative humidity are the factors affecting drying speed. After all, it's only evaporation of moisture.

A solar kiln is very similar to a greenhouse so, yes, you can use your greenhouse for drying lumber. Just follow the established guidelines for air flow and the area of the solar collector vs lumber volume.


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## Yellowbeard (Apr 26, 2015)

I've been looking at the Virginia Tech plan for a solar kiln for a while now and thinking about building it. If you do this, I would sure love to know how it turns out. If I had a place to build one, I would have already done it and be drying all this damn walnut that's lying around. Drying and storage are soon going to be big problems for me.


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## Dave Boyt (Apr 27, 2015)

Another consideration about temperature is killing bugs. At least 135 deg F, long enough to get to the center of the boards & hold temp for at least an hour. That would require insulation. Instead of old boards on top, you might use metal roofing painted black to help get the temp up a bit. Perhaps a better question would be, "has anyone used the VA tech solar kiln as a greenhouse"? Yellowbeard, bring your walnut on up to me, & I'll make sure it doesn't get in your way any more.


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## Yellowbeard (Apr 28, 2015)

I'll keep that in mind, Dave.


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