According to wikipedia, "A kotatsu, used almost exclusively in Japan, is a low, wooden table frame covered by a futon, or heavy blanket, upon which a table top sits. Underneath is a heat source, often built into the table itself." - source
This instructable will teach you how you can build one for yourself for those cold winter months.
The legs on traditional kotatsu are 36cm (about 14.5") tall. When I was in Japan, I found this to be way too short for me to sit comfortably which is why the Ikea LACK works so well. The LACK also has a lower shelf portion which can be used as the final tabletop.
This can also be already assembled or unassembled. It can also be whichever size and color you feel fits your home. I used the bigger size.
- Kotatsu heater
The hardest piece of equipment to obtain. Try BeNippon or Ebay.
IMPORTANT: Kotatsu heaters are designed to be mounted upside down and have no required clearance. Do not use any heating element but a kotatsu heater otherwise you run the risk of starting a fire!
- A 120 V to 100 V step-down voltage transformer
The second hardest piece of equipment to obtain. American outlets put out 120 V but Japanese appliances run on 100 V. Try searching Google, Ebay, and Amazon. This is the one I purchased from Amazon but is no longer in stock. Look at your heater and see how much wattage is required to run it. You'll want your transformer to be able match that.
- 4 angle/L brackets
Get these at any hardware store.
IMPORTANT: Make sure that the screws that came with your kotatsu heater fit the bracket AND that the sides of the brackets are long enough to accommodate the thickness of the heater unit.
- Screws or nails that fit your angle brackets
These will be used to attach the brackets to the bottom of the LACK.
Just take a look at your brackets and get the right number and size of screws or nails to properly secure the bracket to the table. I used screws.
- Comforter/blanket thing
Based on the size of LACK that you have, you will need an appropriate sized comforter/quilt/blanket. It needs to be large enough to fit over the top of the table and have some slack to cover the people sitting under it.
Thickness depends on how warm you want it to be.
As far as design goes, feel free to go wild. It can be in any print you can find that will match your home or you can even make it yourself!
- Electric drill and proper drill bits/screwdriver tips
If you end up using screws, this will make drilling pilot holes and screwing in the screws much easier.
- 4 Washers
For securing the kotatsu heater to the brackets.
If you don't like the LACK shelf as a tabletop, you want a different color, or perhaps you want one that fits EXACTLY, getting a custom tabletop may interest you.