Kilns

[SDM]

Hello everyone looking to get back to milling again and need to start kiln drying my lumber. I'm curious as to which type/style of kiln works best for beams and slabs.  My first project is a large poll barn. I want to make it with large beams (10x10x17) that I plan to have pressure treated. I was told I need to get the moisture content way down for that process to be effective.                          It's been a long time since I've been on the forum and look forward to getting reacquainted with everyone.  I own and operate a tree service in Ga. and therefore I come across an amazing amount wood. My mill sat for 2 yrs and needed a lot of attention. The good folks at Wood-Mizer in Newnan Ga are bringing it back to life and said it would be ready in early Jan. Any advice on kilns would be greatly appreciated! Thanks  Shawn

[blackhawk]

Any kiln will dry large beams and slabs.  The difference is in how long that it will take.  If you are drying from green, a vacuum kiln will definitely be the fastest option.  Idry is the hot name in vacuum kilns these days.  I don't have first hand knowledge of the Idry kilns, but have heard mixed reviews on them.  

[scsmith42]

Any kiln will dry large beams and slabs.  The difference is in how long that it will take.  If you are drying from green, a vacuum kiln will definitely be the fastest option.  Idry is the hot name in vacuum kilns these days.  I don't have first hand knowledge of the Idry kilns, but have heard mixed reviews on them. 

Broadly speaking, vacuum kilns fall into two categories. Deep vacuum and intermediate vacuum.

Deep vacuum kilns dry down to 95% vacuum or more. Because heat does not convect in a full vacuum, some method of introducing heat is necessary in order to vaporize the water and dry the lumber. Options included hollow metal plates in-between the layers of lumber. A hot water / antifreeze mixture is pumped through the plates in order to introduce heat into the lumber for drying. Another option (not used much) was the use of heating blankets in-between the lumber layers.

Still another option is the use of radio frequency to heat the lumber. Typically there are anode and cathode plates placed in-between the stacked lumber and radio frequency (microwave band) is introduced into the kiln, causing the water molecules to heat up. RF and Microwave kilns are the same thing.

Intermediate vacuum kilns such as the iDry system use heat convection to vaporize the water. Lumber is stickered in the kiln chamber and fans circulate warmed air through it to vaporize the water. They were developed by Vacutherm back in the 1980's before Vacutherm transitioned into deep vacuum kilns. About 6 years ago the son of Vacutherm's founder reintroduced the technology as the iDry system.

There are several manufacturers of deep vacuum kilns in North America. PC Specialties was one (vacdry.com), but I think that they are now closed due to the principle aging out. Vacutherm also has their Vacupress line which uses hot water plates to heat. RF Kiln Tech in Canada is a third, and there are a couple more that I'm forgetting the names of. There are some Chinese manufacturers of vacuum kilns.  Originally their products had a reputation of failure after a couple of years due to use of carbon instead of stainless steel, and low grade electrical components. One of the leading producers - Shuowei- is now in their 7th generation and reportedly has all of the early problems resolved.

Hands down, the most affordable and proven vacuum kiln currently on the market is the iDry system, which are available in the $50K range on up.  But an iDry is not necessarily a good choice for thick beams unless they are a fast drying species such as pine or poplar.  Forget using them for thick oak (10/4 or thicker). Deep vacuum kilns cost much more - most start around 2X to 3X the price of the iDry. 

The RF Vacuum kilns from Shuowei are very competitively priced, and if they indeed have all of the bugs worked out they are worth looking into.  For thick beams, this would be my first choice to research.

There are compromises with each technology. The hot water plate system seems to be the most consistent and prevalent technology. There are conflicting reports regarding the consistency of results obtained from RF Vacuum kilns. iDry has brought affordable vacuum drying to many small and mid size operators.

[Stephen1]

A great explanation by Scott. 
I have an Idry standard, and  it does not dry Beams (10x10) fast. A pine 10x10 would take me 5-6 weeks at least, at I am not eve sure about that as I do not even want to try., anymore.
The  most I will do is fireplace mantel of hardwood or softwood , and I put them on the top of a load ( as a baffle if I need space filled) and run them for 12-14 day cycle. The Idry will bring it down to %20 range but that is mainly surface moisture, the core will still be quite high.

[doc henderson]

SDM what is a MC that is way down?  Have they given a %?  How many beams this size are you talking about?  What species?  Do you need the whole beam PTed or just what goes in the ground.  I am assuming a pole barn is like what we have in Ks.  If the sides are closed in, does the whole length need to be PTed.  Sorry if these questions are not on track, but maybe traditional kiln drying and pressure treating is not the best answer.

Also, will you produce all the beams at one time, or as they become available?