Rocket Wood Kiln

Hi all, been a while, I have been too busy doing to be talking recently.  I did finish a grey water system that is working very well so I actually have something to show for it, which is nice.

Now, for something else. I have been intrigued by the rocket heaters and it seems with a little work, I can use it to dry wood. I currently have a kiln that runs off electric but the cost isn't pleasant, and I am overrun by scrap wood anyway.

So, to the brain trust here, can you help me in what to do to make a rocket heater for a kiln? Too high of temperatures are a bad thing, but constaint temperatures aren't as necessary. Figure, maximum temperature shouldn't be more than 150 degrees in a box that holds 1500 BF.

Of course, being fireproof is incredibly important since as the wood gets dry, you have LOTS of kindling just waiting for a spark.

Thanks all

Well, I picked up the book and there was an example of one person doing this. Looks interesting - so it is off to experimenting.

What kind of dimensions are you looking at for that lumber?  Also remember rocket stoves are manual feed so it won't be start it then walk away and forget it.

Part of the challenge will be creating some kind of automatic feed. Also, it is a good thing in a kiln to heat up, and cool down. It allows the wood to relax and equalize moisture from outside to inside. Bringing the temperature up to 130 F and then letting it come back down to 80 to 90 would be just fine. Also, remember I am in the tropics, which means I start at about 80 F and it never gets cold.

Using 8' lengths of wood as a standard and 1x6 dimensions I work out an 11' wide x 3' high x 8' long chamber or a 6' x 6' x 8', this includes about 1/2" spaces for stickering the wood.  If you build such a chamber with the exhaust runs in thick walls of cob and insulate it well, I understand your in the tropics, you can determine how much firing is needed to attain the 150 degree temperature.  The insulated thermal mass of the walls will then hold the temperature for an extended period and cool slowly which is good for drying wood as it allows stresses to be released slowly keeping checking down.  Basically make a large hollow bench and insulate the outside.  Have an insulated loading door at one end and the firing chamber at the other.  The mass of the clay wall will act as a fire barrier so your newly dried "kindling" won't go up in smoke.

In the rocket evaporator thread, I posted the following diagram, to illustrate a basic principle I think could apply here:

A part of the chimney not too far from the exhaust can be used to heat incoming air; moist air can be used in combustion; and an insulated section of chimney can drive air through the system very rapidly. The important thing is to make sure that the easiest path for air to get into the fire is through the whole kiln; this means the system should have a ridiculously-overpowered updraft.

As with the maple syrup idea, using air as a heat-exchange medium can make fire a lot less likely: the coils of a hairdryer are red hot, but few people light their hair on fire.

Naturally, the tub of maple sap in the diagram should be replaced by a stack of drying lumber.

If there's significant thermal mass in that insulated section (e.g., if the updraft tube is built of brick), a short fire in the morning can drive airflow for a long time, allowing forced air without as much heating. A sheet metal cowl that covers the pipe and interferes with heat transfer to the air intake would enhance this effect.