Today I’m going to take you through the process of turning an old fridge into a kiln. From this point forward we’ll refer to it as the aptly named “Kilnerator.”
The kilnerator is great for drying out green (wet) lumber, which is its sole purpose in my shop. This kiln design is simple as it does not need a dehumidifier, fans, or even a thermometer to work. This design relies solely on the heat generated by a single incandescent bulb to create a convective current in the kiln and dry the wood.
So, what do you need to get going?
- Used fridge, preferably not a side by side
- Cleaning supplies if fridge is disgusting
- 1/16″ – 1/2″ drill bit set
- Ceramic light socket
- Incandescent light bulbs: 40w, 60w, & 100w, 1 of each
- Light switch
- Light switch wall plate
- Electrical box
- Extension cord
- Wire nuts, assorted
- Screws, drywall or sheet metal, assorted
- Shelving material
- Thermometer/hydrometer (optional)
- Power drill
- Reciprocating saw (optional)
- Flathead screwdriver
- Wire Strippers
- Bolt cutters/angle grinder
- Your own personal awesomeness (required)
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Building the Kilnerator
So, you’ve got the fridge, supplies, and a fresh helping of awesome. Now what?
First off, take out the shelves and drawers and clean that sucker out. Chances are it’s smelly and slightly gamey. I kept the drawers to use as storage bins elsewhere in the shop and reused the shelf supports that were originally fitted with glass. I sprayed down my fridge with mold killer (just to make sure) and then followed up with some 409. Do please be sure if using two different cleaners to not mix them, since you could inadvertently make some nasty chemical reactions.
Now that things are cleaned up, it’s time for some modifications! If you’re fridge is like mine with the freezer box above or below the freezer, then either drill a handful of 1/2″ holes in the divider separating the two, or remove it completely. Have fun here if you take out this divider! The sledge hammer, sawzall, and your own inner redneck are all acceptable tools! By removing this divider, you’ll get better air flow to the top section and reduce the size limitations of your kilnerator.
I put five 1/2″ holes in the top and bottom of my kilnerator and laid them out as a square with one hole in the center to not concentrate the airflow in just one area. If you leave the refrigeration system intact, be mindful to not drill through any of the components during this operation.
Now it’s time to add the light bulb. Drill a hole on whatever side of the fridge you’ll be mounting the light switch. The hole should be similarly sized to the power cord you’re using (mine was 3/8″.) Cut off the socket side of your extension cord and wire up the light socket as shown below. Run the cable through the hole previously drilled and attach your socket to the floor of the kilnerator. Some people will put a cowling over the bulb for a little extra protection from water dripping on it or accidentally breaking the bulb while loading or unloading.
Go ahead and attach the receptacle box at a comfortable height and run the cable into the box. Wire up the switch and close up the receptacle box.
I’ve intentionally not given a diagram or photos of wiring the electrical components because 1-I’m not an electrician and 2-I don’t want anyone who doesn’t know what they’re doing to try and give me grief if they burn down their house 🙂 There are tons of resources online that cover basic wiring. This site is a great resource and one that I’ve visited in the past when taking on a new electrical project. Above all, use common sense and ask for help if you don’t feel comfortable with this step!
Ok, so now we need to cobble together some shelves. I bought wire shelving used for closets and cut it to size for the supports in my kilnerator. You’ll need either bolt cutters or an angle grinder with a cut off wheel to cut through this shelving material. Zip ties are all I used to marry the wire shelving and supports. If wire shelving doesn’t do it for ya, then let your imagination run wild. Anything from wood dowels and 2 x 4’s to a PVC pipe jungle gym will serve the purpose.
The final touch for this project is adding a wireless thermometer & hydrometer. This item is completely optional though. I put mine in the upper section of the kilnerator so that I didn’t get skewed temperature readings from close proximity to the light bulb. A couple screws and batteries are all I needed.
How To Use Your Kiln
Great, you’ve effectively rendered a fridge useless and created a gigantic light box with some holes in it…Now what?
I generally use my kilnerator for drying wooden bowls as a step in the woodturning process. However, it can also be used for drying small to medium sized pieces of lumber.
The process is simple. First seal the end grain of your boards or bowls with a green wood sealer and let it dry. I use Green Wood Sealer made by Klingspor because it’s much cheaper than Anchor Seal and works just as well.
I typically let my boards & bowls air dry to between 20-30% MC (moisture content) before putting them in the kilnerator. My target MC is 9%, but if I’m in a hurry 12% MC is ok.
When loading the kilnerator, I’ll put the drier pieces closest to the light bulb. So with the boards and bowls between 20-30% MC, I start off with a 40w incandescent bulb and let it cook for about a week. After a week or at about 16% MC, I switch to a 60w bulbs and leave that on for another week. If it’s winter time or I’m just in a big hurry, then I’ll swap out the 60w for a 75w bulb when the pieces reach 12% MC and let the kilnerator cook for again, another week. Once everything is around 9% MC, I’m happy and done drying the wood. At this point it’s very important to let the bowls and boards cool down slowly. If you simply pull everything out of the kilnerator and don’t quell your excitement, you run a serious risk of having your pieces crack from cooling too quickly.
That pretty well wraps it up. Leave any comments or questions below and I’ll do my best to answer any questions you may have. Thanks for reading!
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