DIY Kiln

[RP Tree]

Hello,

 

I recieved my Alaskan mill the other day, (thank you Rob for a prompt service) I'm about to start milling some spalted beech I have and i'm looking to build my own kiln.

 

I don't have room for an old freezer box so I thought I would insulate a shed I have. My question is what size of dehumidifier should I buy?

 

The shed isn't too big, about 5' wide by 10' long and around 6' high. Should I buy as big as I can afford? My budget is around £200. Or can I get away with a smaller one?

 

Also is there a book on the subject anyone can recommend? Any help would be great or links to other relevant threads (I have done a search!)

 

Cheers

 

Richard

[wills-mill]

There's some fantastic information on Woodweb.com if you need to get some very sound opinions on milling and drying, on a large and small scale.

 

Search Results from WOODWEB's Site Search Engine

 

From what I've read in the past, a lot of folk don't recommend using domestic or light industrial dehumidifiers for timber drying as the acids and tannins from the timber will corrode the internals of the machine. I've not had any experience of using them myself tho....

 

Don't send a home dehumidifier -- to do a commercial kiln's work

[Big J]

I run a DIY kiln that operates with a combined dehumidifier and heat vent system.

 

The dehumidifier is a fickle beast (an old Ebac BD150) and has had a new auto defrost timer (got stuck on defrost, rather than cooling) and still isn't working properly. It now doesn't defrost, so you can't turn it on until the temperature is over 25 degrees, or it ices up.

 

My point is that there is probably some truth in the notion that using non-timber drying dehumidifiers can be problematic. However, on a DIY scale, they are far far cheaper, and provided you monitor the environment in the kiln, you will be fine.

 

My kiln is as follows:

 

* Ebac BD150 dehumidifier

* 835w Carpet drier to circulate air

* 2100w oil filled radiator

* 75w extractor extracting 210 cubic metres of air an hour.

 

The heater is on a thermostat at 37 degrees, and the extractor runs on a timer meaning it runs for 50% of the time.

 

The kiln has a capacity of around 280-310 cubic foot of timber, and dries quite happily from green in 8 weeks (with certain constraints on board thickness - for instance Oak above 1.5 inches takes 12 weeks, though most other timbers are OK up to 2 - 2.5 inches). It's actually just been switched on and the dehumidifier is removing 84 litres a day and the extractor 60 litres. This will go down considerably in the coming days, but there is 3400 litres of water to extract to get the timber down to 10% moisture content.

 

Very important as well is a wireless weather station, so that you know what the temperature and humidity in the kiln is. You can get them for about £20-30.

 

I would seriously consider trying to make space for a freezer box if you can. You can get the backs off the supermarket delivery trucks that are a lot smaller. You need it to be well insulated and airtight, and it will prove more expensive to try to make it yourself. I got my kiln (an 18ft freezer box) for £500 delivered.

 

Regarding the size of kiln that you have specified, you will have a capacity of about 90 cubic foot. Go for a dehumidifier with a 30 litre a day extraction rate. In addition to that I would seriously consider getting a separate heater and extraction system as I've found that the dehumidifier cannot extract beyond a certain point (insufficient free moisture in air, whereas a heater/extractor combo can continue to remove water).

 

Spalted beech can be troublesome in the kiln. It's already so full of mildew and bacteria that when you put it into a warm environment it goes nuts and can look quite unattractive in the end. That is just my experience though!

 

Good luck with it - would like to see any progress photos as they happen.

 

Jonathan

[Rob D]

I'd just buy a dehumidifier off ebay to start with. If you keep an eye open you'll get one for a good price although summer time is when the real bargains are.

 

Other than that as Big J says above.

 

Do a bit of reading on the net but don't worry overly much as experience is one of the best teachers.