Dry kiln plans

[StoddardLumber]

Hi all did a little searching but did not find any plans yet. I am looking for plans for a small wood fired dry kiln ( not a direct fire but using an air to air heat exchanger)

If there are no plns can anyone point me in the right direction for air flow numbers and btu values and velocity values?

[GeneWengert-WoodDoc]

Species?  Thickness?  Incoming MC? Kiln volume in BF?

It would seem that the information about the burner, fuel feed and heat exchanger would come from an engineering source.  Safety (fire) concerns and smoke would be major issues.  If this is a commercial kiln, then many states have regulations that must be followed concerning a burner, probity to another building, annual inspections and so on.  In any case, you would be wise to check with your insurance company to make sure that a fire that spreads to the house, shop, garage, etc. is covered by insurance.  In general, because of all these safety issues, very few homemade burners are made for dry kilns; rather commercially built units are used.

As a general guideline, you will be looking at 3 to 5 million BTU per 1000 BF for drying and building losses.  This is the energy coming from the heat exchanger, so you would have to add boiler and heat exchanger efficiency factors to these numbers.  These numbers are also AVERAGE.  When first starting the kiln with frozen lumber, energy use for the first 24 hours would be higher than at any other time.

Another issue to consider is whether you want to achieve uniform final MC and also achieve stress relief (also called casehardening relief).  these two are hard to accomplish without a source of steam from a small boiler.  If I knew more about your plans, I could be more specific.

[red oaks lumber]

nyle has kiln plans. i use an outdoor wood stove and run a supply line of hot water to a modine style heat exxchanger, mine is rated for 350,000 btu's .
my kiln chambber holds 15,000 b.f. and that heat exchanger does a very good job heating the whole load,  even frozen lumber.
i would recommend using a nyle d.h. kiln unit, they have all the issues of drying lumber taken care of.

[StoddardLumber]

Thanks for the replies

Doc I plan to dry pine red oak and firewood.  That said I realize there are a lot of issues with drying lumber vs firewood.  So my plan is to start simple build a chamber that will hold 3 to 5000 feet and be able to achieve 180 deg kiln temp. I want to basic lug put a wood stove in an insulated room such that I can load it from the outside and blast heat into the room. From there I can add controls to vary the heat level and humidity.

Now I know this is less than optimal for lumber but perfect for firewood. But I know pine is fairly forgiving and could be made to work but it may not work well

As I build more hardwood markets I will look to getting a commercial steam boiler as the heat source and then temp and humidity control will be no problem as it will be standard dry kiln stuff.

One of my biggest questions is how come standard dry kilns are heated from the top and the hot air is pushed down through the stack? I have a setup where my heat can be below the stack and let convection move it up and use the fans to recirculate the air? Am I missing some fundamental of the kiln operation or is it just easier for insulation and use to have the heat above?

[GeneWengert-WoodDoc]

There are a good number of kilns that have air moving horizontally, rather than vertically.  Often such kilns were called side-winders.  I think the reason for fans overhead is that we had steel, aluminum structural members available at low cost in this country, so up was not expensive.  Also, the original kilns had heat underneath, so moving fans above kept the same footprint...so, it is historical.