Another Kiln Build. 20 x 10 x 8 Indoor Dehumidified and Heated. First Build

[Mr.Green]

Hi All.  I am new to this Forum and fairly new to wood processing and very new to wood drying.  I live in NC near Winston Salem and I purchased a large 6' x 11' CNC router over 1 year ago. I have a 36" wide belt sander and a few other smaller tools.  I have been getting into cutting and planing slabs and lumber for local wood workers and I have started processing my own slabs to sell recently.  I have a large shop and I have enough room to build a kiln indoors.  I already purchased a bunch of the materials before I found this forum.  I am starting the build today.  My current plan is as follows:

20 long, 10 deep, 8+ high (+ additional height for fans)
Side opening barn doors for loading / unloading. (2 swing open doors both 10' x 8')
1 'Man Door' with added insulation.
2x4 construction with R13 fiberglass insulation.  
Outer skin is Asphalt Impregnated Sheathing 1/2".  This will add some R value.
Inner walls will be vapor lined for now.  I will most likely add solid interior walls in the future.
This will be built indoors on a concrete floor.  I plan on setting foam panels on floor for insulation if necessary.

I have a fork lift.

I would like to be able to heat the kiln to desired temps for proper drying and then also for sterilizing.

I have not purchased the fans, dehumidifier or heater yet.  I plan on purchasing a commercial dehumidifier unit and control the heat and humidifiers with something like this (Is this that much less accurate than dry / wet bulb ?):
Amazon.com : Inkbird ITC-308 Temperature Controller with IHC-200 Humidity Controller : Garden & Outdoor

Can you please give me an idea of what size dehumidifier I should plan on purchasing?  What H20 capacity per day should the unit be rated for? I realize that there are calculations for all of this (and I am sure that I will do them at some point here soon) and there are already Kiln packages available from companies, but I am frugal, not afraid to do things myself and I have Youtube.  Perfect recipe for disaster .  If someone with some experience can help save me some time, effort or mistakes I would be very grateful.  I realize that I have a steep learning curve in front of me.

Any help with the design, component recommendations, etc would be greatly appreciated.  I wish I would have started this thread a week ago .  I am leaving for my shop right now to start building this, please hurry!  I will post some pics of the build.  Thanks!

[K-Guy]

My advice would be don't use fiberglass insulation. Use polyiso instead.

[Mr.Green]

My advice would be don't use fiberglass insulation. Use polyiso instead.

That is a big step up in $.  Can you elaborate?  Thanks!

[K-Guy]

Fiberglass will absorb moisture when the kiln leaks, I say when because like a tire eventually it will. Polyiso is moisture resistant.

[Mr.Green]

Fiberglass will absorb moisture when the kiln leaks, I say when because like a tire eventually it will. Polyiso is moisture resistant.

Do you mean leak from the outside in or from the inside into the insulation?

[K-Guy]

Due to the constant expansion and contraction of the chamber from heating and cooling over time the kiln will leak from the inside to the insulation.

[Mr.Green]

I got to put in a few hours on the build today.  I will build a large header to go above the two front 10' x 8' swing open Barn Doors.  The roof will be slanted from the back wall to the top of the header, the fans will be up near the front above the doors behind the header.  It will be a couple of days before I get back to working on her so please give me some feed back so I have some time to react !   Thanks again.

[K-Guy]

Put in an insulated floor or you will have heating problems.

[scsmith42]

Howdy Neighbor!  I'm about an hour and a half east of you.

Several comments.

First and foremost - most consumer and commercial dehumidification units are not suitable for a wood kiln environment.  They do not have a high enough temperature threshold and they are not corrosive resistant.  Many of them shut off at 104F, and most DH kiln drying is done between 90 - 120F, so that's a problem.

I'd highly recommend a Nyle L200 for the size loads that you want to dry.  Source your fans from them as well because they are designed for a kiln environment.

Second - Stan's advice is spot on.  Don't use fiberglass insulation; you will regret it.  DH kiln temps typically vary between 90F - 160F, and there will be a lot of structural movement over that span of temps.  That means leaks into the walls and the fiberglass will not live well.

Third - you will want two man doors on the ends - one on each side of the lumber stacks so that you can visually check status and take MC% readings as required.

Fourth - insulate the floor or it will be a big heat sink.  You will see a variance in the drying conditions between the lumber at the bottom of your stacks versus the lumber at the top.

Fifth, there are times that you need to vent the kiln.  Are you planning to run some duct work through the walls or ceiling?

Best of success to you.

Scott

[Mr.Green]

Howdy Neighbor!  I'm about an hour and a half east of you.

Several comments.

First and foremost - most consumer and commercial dehumidification units are not suitable for a wood kiln environment.  They do not have a high enough temperature threshold and they are not corrosive resistant.  Many of them shut off at 104F, and most DH kiln drying is done between 90 - 120F, so that's a problem.

I'd highly recommend a Nyle L200 for the size loads that you want to dry.  Source your fans from them as well because they are designed for a kiln environment.

Second - Stan's advice is spot on.  Don't use fiberglass insulation; you will regret it.  DH kiln temps typically vary between 90F - 160F, and there will be a lot of structural movement over that span of temps.  That means leaks into the walls and the fiberglass will not live well.

Third - you will want two man doors on the ends - one on each side of the lumber stacks so that you can visually check status and take MC% readings as required.

Fourth - insulate the floor or it will be a big heat sink.  You will see a variance in the drying conditions between the lumber at the bottom of your stacks versus the lumber at the top.

Fifth, there are times that you need to vent the kiln.  Are you planning to run some duct work through the walls or ceiling?

Best of success to you.

Scott

Thanks for the advice!  I will seriously consider the Nyle products.  I plan on having at least 1 Man Door in one of the barn doors and possibly one door at one end of the kiln.  2 of the walls are built up against the brick walls in the corner so I cant add a door on one of the ends. My plan was to stack some foam insulation boards on the floor, removable during loading / unloading if necessary.  I will also consider foam boards for the walls.  Is the issue with fiberglass insulation really the humidity from the inside?  I am trying to not brake the bank on this, but if it is necessary I will consider different insulation.  I am planning on running a vent, not sure where yet, but I may be able to run it directly outside.

[scsmith42]

Howdy Neighbor!  I'm about an hour and a half east of you.

Several comments.

First and foremost - most consumer and commercial dehumidification units are not suitable for a wood kiln environment.  They do not have a high enough temperature threshold and they are not corrosive resistant.  Many of them shut off at 104F, and most DH kiln drying is done between 90 - 120F, so that's a problem.

I'd highly recommend a Nyle L200 for the size loads that you want to dry.  Source your fans from them as well because they are designed for a kiln environment.

Second - Stan's advice is spot on.  Don't use fiberglass insulation; you will regret it.  DH kiln temps typically vary between 90F - 160F, and there will be a lot of structural movement over that span of temps.  That means leaks into the walls and the fiberglass will not live well.

Third - you will want two man doors on the ends - one on each side of the lumber stacks so that you can visually check status and take MC% readings as required.

Fourth - insulate the floor or it will be a big heat sink.  You will see a variance in the drying conditions between the lumber at the bottom of your stacks versus the lumber at the top.

Fifth, there are times that you need to vent the kiln.  Are you planning to run some duct work through the walls or ceiling?

Best of success to you.

Scott

Thanks for the advice!  I will seriously consider the Nyle products.  I plan on having at least 1 Man Door in one of the barn doors and possibly one door at one end of the kiln.  2 of the walls are built up against the brick walls in the corner so I cant add a door on one of the ends. My plan was to stack some foam insulation boards on the floor, removable during loading / unloading if necessary.  I will also consider foam boards for the walls.  Is the issue with fiberglass insulation really the humidity from the inside?  I am trying to not brake the bank on this, but if it is necessary I will consider different insulation.  I am planning on running a vent, not sure where yet, but I may be able to run it directly outside.

I'd skip the door in a door plan and just put two doors on the exposed end wall.  The problem with the door in a door is that it severely weakens the larger door.
The temp foam on the floor will help, especially if you put your lumber on pallets and then fill in around the pallet with the foam boards.  This will also serve to baffle the ends of the pallets; forcing the air through the lumber stacks instead.
During the initial portions of the kiln drying process it will be extremely humid inside, and moisture will escape and condense.
Re the vents - you need two - one from the suction side of the fans and one on the pressure side.

[Mr.Green]

I'd skip the door in a door plan and just put two doors on the exposed end wall.  The problem with the door in a door is that it severely weakens the larger door.
The temp foam on the floor will help, especially if you put your lumber on pallets and then fill in around the pallet with the foam boards.  This will also serve to baffle the ends of the pallets; forcing the air through the lumber stacks instead.
During the initial portions of the kiln drying process it will be extremely humid inside, and moisture will escape and condense.
Re the vents - you need two - one from the suction side of the fans and one on the pressure side.

Thank you for the reply and the advice.  I have a nice big vent going to the outside directly behind that back wall, I will make an access hole to it.  Would I need more than 1 man door? Is it because the stacks should be tight up against the wall / door to block air flow?  I planned on being able to maneuver around in there a little bit, the thing is huge in my opinion.  I may have built this kiln too big .

[scsmith42]

You need room between the stacks and the front/rear walls for air flow.  This space is referred to as a plenum.  

The ends of the stacks should be baffled to the side walls so as to force the air through the layers of stickered lumber.

Typically you will want to take regular moisture content readings on both the air inlet as well as air exhaust sides of your stacks; hence the advice for two doors - one into each plenum.

[customsawyer]

Also need to have a plan on what to do with the water from the kiln. Depending on moisture content of lumber going in, I've pulled over 20 gallons of water a day from some loads.

[Mr.Green]

I have a drain near by that will work great for getting rid of the water.  If I was to try to use a commercial dehumidifier for a while, can they be ducted so they are not in the heat of the kiln?  If not, is there any harm in only running the kiln as hot as the dehumidifier will allow and not use the dehumidifier during the sterilizing phase? I am not necessarily trying to dry slabs as fast as possible right now.  This could change in the future, but for now I can be patient if necessary.  Thanks for all of the input, greatly appreciated!

[scsmith42]

I have a drain near by that will work great for getting rid of the water.  If I was to try to use a commercial dehumidifier for a while, can they be ducted so they are not in the heat of the kiln?  If not, is there any harm in only running the kiln as hot as the dehumidifier will allow and not use the dehumidifier during the sterilizing phase? I am not necessarily trying to dry slabs as fast as possible right now.  This could change in the future, but for now I can be patient if necessary.  Thanks for all of the input, greatly appreciated!

With thick slabs you typically want to dry slow, so keeping the temp under 100F is doable.  Might take a while longer to pull the water from the core though.  
Whether it's inside the kiln or not, the coils will still be exposed to the kiln heat when the air is ducted through them.