Building a kiln

[Hodge]

Evening all, I'm thinking of building a kiln out of an old fridge unit off a 7.5 tonne lorry. Any idea how long it would take to dry a builders bag of hard wood? I know this would differ if there was more than 1 bag in. I know some of you guys have them for planks etc so any help would be much appreciated.

[Big J]

Hard to say exactly how long it would take to dry the timber. You could be very aggressive with your kilning to speed up the process - a luxury us miller can't afford as it would destroy the aesthetic and structural properties of the wood.

 

At a real push you would be able to get 20 standard builders bags into an 18ft box (900x900x900mm, not cubic meter). You need air flow, and lots of it. Carpet dryers are very good for the large amount of air they move for the relatively small space they occupy.

 

I wouldn't bother with a dehumidifier - they can be unreliable, and don't operate above 35 degrees c (assuming a standard building dryer, not a specific timber dryer, which is very expensive). Basically, have an extractor at one end, a vent at the other, 3kw of heaters in between with a carpet fan either side. Make sure to keep a minimum of 6 inches of air space down each side of the stack. No airspace means no air movement. Also, put the bags on pallets so that the air can get underneath too.

 

I would think that if you had the firewood cut fairly small (no more than 3x3 inches by whatever length) then you should be able to get it dry in 6 weeks to 20%. Bear in mind that you will have the best part of 5kw of electricity running through the kiln, costing almost £600 over the course of the cycle.

 

Jonathan

[Hodge]

Hard to say exactly how long it would take to dry the timber. You could be very aggressive with your kilning to speed up the process - a luxury us miller can't afford as it would destroy the aesthetic and structural properties of the wood.

 

At a real push you would be able to get 20 standard builders bags into an 18ft box (900x900x900mm, not cubic meter). You need air flow, and lots of it. Carpet dryers are very good for the large amount of air they move for the relatively small space they occupy.

 

I wouldn't bother with a dehumidifier - they can be unreliable, and don't operate above 35 degrees c (assuming a standard building dryer, not a specific timber dryer, which is very expensive). Basically, have an extractor at one end, a vent at the other, 3kw of heaters in between with a carpet fan either side. Make sure to keep a minimum of 6 inches of air space down each side of the stack. No airspace means no air movement. Also, put the bags on pallets so that the air can get underneath too.

 

I would think that if you had the firewood cut fairly small (no more than 3x3 inches by whatever length) then you should be able to get it dry in 6 weeks to 20%. Bear in mind that you will have the best part of 5kw of electricity running through the kiln, costing almost £600 over the course of the cycle.

 

Jonathan

 

Cheers big j! That's great info. Thanks.

[Big J]

No worries!

 

One thing that I forgot to add is be very picky with your species. Avoid Oak at all costs as it hates being dried. Sycamore, Elm and to a lesser extent beech are your friends!

 

Jonathan

[Hodge]

I'm not sure it would be economically viable, 600 quid for the electric, then the wood on top, I don't think I could make a lot of profit, I maybe could get 70 quid a bag round here.

[Rob D]

Not worth your while I'd say. I'd cut it all now and then air dry as usual outside somehow for next year.....

 

Unless you have a massive set up kilning logs is prob not worth it.

[Big J]

I am inclined to agree.

 

The most efficient kilns are heated by furnaces fed by offcuts. The most local on of those to me cost almost £50,000 to set up though.