vacuum kiln-dried wood

[Dave Lehnert]

I found a local Hardwood dealer that advertises "vacuum kiln-dried wood"
I am not familiar with Vacuum dried wood, What are the advantages or is it just another way to dry wood?

[Jim Becker]

It's a fast and efficient way of extracting moisture out of wood, especially thicker stock. It uses a combination of heat and vacuum to do what it does. Dry times are substantially shorter for the kiln...like a few days rather than weeks. Matt Cremona on the 'Tube has been using a vacuum kiln operation owned by a friend of his to get his slabs and thick bench components dried for some time now.

[Walter Plummer]

Canadian Woodworks is another You Tube channel that has both conventional and vacuum kiln. Here is his video explaining it. https://www.youtube.com/watch?v=8Xi4bBwO2QM&t=573s

[Richard Coers]

Biggest advantage is extremely low degrade from drying in a very short time. In a hard vacuum, water will boil at 90 degrees F. So wood never gets much over 90 degrees. Radiant heat won't work in a vacuum, so there is a heat source between every layer of wood. High end units use aluminum plate sandwich which hot water is pumped through. Woodmizer sold one for a while and used an industrial electric blanket between layers. Biggest disadvantage is the expense of the unit plus it will not be perfect on wood that has variable density in the same board. So straight grain approaching heavy crotch grain will very likely not have the same moisture content from one end to the other. Other expensive is the vessel that has to withstand the high vacuum.

[Scott T Smith]

Biggest advantage is extremely low degrade from drying in a very short time. In a hard vacuum, water will boil at 90 degrees F. So wood never gets much over 90 degrees. Radiant heat won't work in a vacuum, so there is a heat source between every layer of wood. High end units use aluminum plate sandwich which hot water is pumped through. Woodmizer sold one for a while and used an industrial electric blanket between layers. Biggest disadvantage is the expense of the unit plus it will not be perfect on wood that has variable density in the same board. So straight grain approaching heavy crotch grain will very likely not have the same moisture content from one end to the other. Other expensive is the vessel that has to withstand the high vacuum.

Excellent explanation Richard.

The only two things that I would add is that there is a hybrid vacuum kiln called the iDry that uses a lower vacuum and convection heat for drying (stickered stacks with hot air circulation), and that there are also hard vacuum kilns that sandwich aluminum plates between the layers but use microwaves instead of hot water to provide the heat source.

[Frank Pratt]

Radiant heat won't work in a vacuum, so there is a heat source between every layer of wood. High end units use aluminum plate sandwich which hot water is pumped through.

I think you mean conductive heat won't work in a vacuum. Good explanation though.

[John TenEyck]

I think you mean conductive heat won't work in a vacuum. Good explanation though.

Actually, I think he means convective heat transfer won't work in a vacuum.

John