Kiln size - Is bigger too big?

[OregonTimberWerker]

I have a 15x24 space under roof, perfect for a kiln chamber.  Shall I build the kiln to fit the space, or make it smaller?  I plan on drying Douglas Fir with a Nyle L200.  Most of my lumber will be 12' and 16' in length.  What are the draw backs of having a kiln larger than the minimum dimensions needed?

[Crossroads]

I have no experience with this, but would think it wouldn't be very efficient. Might be better to wall off part of it for the kiln and use the open part for air drying. 

[Southside]

It's not the minimum dimensions that are critical, it's the optimum size that matters. Too big and airflow is impacted so drying won't work right. You don't want your stack to be over 42" wide with the 200 or airflow between the boards is an issue. 

[doc henderson]

it will take longer to come up to temp and humidity.  what is the recommended dimension per Nyle?  I think you could go up some, but not too much.  if you did a small load, you would be wasting some energy on the big space.  soft wood can go faster, but to remove that much water, it is a smaller charge.

[YellowHammer]

A chamber that is too big will negatively impact airflow, or you will have to provide baffling to reconfigure the chamber.  Non optimized airflow reduces drying time and increases sticker stain.  

Typically, you'll need 18 inches minimum on the front and back of the stacks of wood to the wall, no space between the bottom of the fan deck and the top of the packs, and less than 6 inches on the sides of the packs to the wall.  You'll need a place for the dehumidifier.  A Nyle 200 can dry up to 4,000 bdft of wood at a load, but is better at 3,500 for hardwood, and can only do 1,500 of green softwood before the dehumidifier becomes overwhelmed.    

[customsawyer]

That is really close to the size of my kiln at 16x22. I use 4 fans across the top and it takes some baffles to force the air through the stacks. It has worked for me.

[rusticretreater]

A lot of air to move around.  As folks said, you will need bigger fans and baffles.  It will take much longer to come back up to temp after you open the doors.  What wasn't mentioned was if this was a dehumidification setup, your heat source, etc.  You could use that spare 7-8 feet to the side to put controls, equipment, drainage.

You could also make two chambers, each with different drying cycles like softwood and hardwood or boards and slabs.

[K-Guy]

If you are going to use a Nyle L200, I've put the manual link below. It has chamber plans in it. For Douglas Fir you will have a capacity of 1500 - 2000+ bf, so a large chamber isn't required. Also plan on extra fans, softwood needs more airflow.

https://www.nyle.com/wp-content/uploads/2021/07/NDK-L200-Manual-2021-V4.3.pdf

[OregonTimberWerker]

Thanks for all of the replies.  That is exactly the info that I needed!

[wkf94025]

Non optimized airflow reduces drying time and increases sticker stain.      

Did you mean increases drying time?

[YellowHammer]

Yes, sorry, typo.  Non optimized airflow will increase drying time, and increase the chance of sticker stain.