Instructables
Picture of Build an American-style kotatsu
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.
 
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Step 1: Materials check

Picture of Materials check
Required:
- Ikea LACK coffee table (Ikea )
  • 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!
Optional:
- 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.
- Tabletop
  • 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.
Emily-RoseM made it!1 month ago

Thank you for the tips... I made my own in Sydney last winter and here it is one year later!

I used the same equipment as you (and I needed the step-down transformer to work from our Australian 240v system). I also picked up a double futon mattress from Freecycle and cut holes through it for the table legs - this made it a more appropriate height for me, extremely sturdy (you can pull yourself up using the table knowing it won't move), and it's very comfortable for sitting on. In fact I've been known to spend many a winter night sleeping underneath :-P

I have little floor chairs that people can choose to use as back supports, and I now have a sofa next to it for those who really aren't comfortable sitting that low down - they still have the option of putting their feet under the blanket.

The Lack tabletop is much denser and heavier than the rest of the table, so it sits sturdy and holds the blanket in place well. It does slip a couple of inches here and there sometimes but it's really not a problem - we've hosted plenty of dinner parties and some late night drinking sessions round it!

I think it makes a really attractive focal point to our living room, just in front of the fireplace as it is, without spending any significant money on its construction or usage. It's the only heating we have during winter... yeah fair enough Sydney isn't known for its cold winters! But when you do feel chilly this warms you up immediately. I've almost never turned the heater up beyond 'minimum'. In fact, when you have a few people sat round it, the shared body heat is enough to generate a good deal of warmth!

The only flaw which I'd love to fix is the way the heater hangs down from the inside tabletop, occasionally getting in the way of my knees. The kotatsu tables in Japan have hollow tabletops so that you can fit the heater flush inside... when I have some more time to look at it I'm going to see whether I can't try to replicate that by adapting / replacing the Lack tabletop. Then it will be truly perfect :-D

Now that we're coming back into summer again, I just slip the blanket off and put it over my bed as a throw.

kotatsu_cosy.jpg
maxim7752 years ago
A 10 V heater in series would be a cheaper way to account for the voltage difference. I suspect a 12 VDC heater (something automotive is what I'm thinking) would be close enough. Be aware that while a heating element won't care, not all DC heaters will work on AC, depending on the control circuitry.
Better yet, why not just use an electric blanket under the comforter (for more insulation)?
PoppyP maxim7751 month ago

For Maxim775 NOW YOU ARE TALKING!

Sigmoid1 year ago
A step down transformer for this application is unnecessary, expensive, and a bad idea all round. Also, it may or may not drive you crazy with its trademark 60Hz hum (in the case of a direct transformer).
Realistically, 120VAC should cause no problem whatsoever. In fact, many sources on the web say that people have been using Japanese kotatsu in the US without any modifications, and haven't experienced any problems whatsoever.
Mains voltages are highly variable even within a country, often easily with 10-15% differences, so appliances are always designed to allow some leeway.
Anaithnid1 year ago
Does the top of the kotatsu slip around much? The bottom shelf of the ikea table doesn't seem to heavy and I fear it might slip around to much and I would have to constantly readjust it. Thank you in advance.
am4d1 year ago
How sturdy is this particular table without the bottom shelf in place?
I assumed the bottom shelf might have been designed to also give the legs support.
Silver Skeeter (author)  am4d1 year ago
The table is just as stable without the bottom shelf. The shelf doesn't provide any additional support actually.
Sadly, the BeNippon site is shut down due to the earthquake a few years ago. Why they haven't reopened since the dangers passed, I do not know.
Silver Skeeter (author)  TimberWolf58711 year ago
That's really too bad!
Hey I just wanted to thank you for your great instructions and pictures. I have searched many a blog about building my own "Kotatsu" and yours by far is the best, I am mostly a visual learner and your instructions are very clear. My boyfriend and I built our table this past fall, with free wood that was thrown out in the woods by our maintenance guys. We only bought stain and sand paper. I am going to be using a king size faux shearling blanket, its super soft and warm! Yeah I was totally lazy this past winter and did not get a heater wish I did. I will now for sure, I have decided on the cozy legs heater, for safety reasons! Also still need a table top, for over the blanket. Then we will REALLY get to try it out, we have just been using the table as a coffee table, since I did not have one. Thanks again, this blog really helped inspire my own "Kotatsu" table. Sorry I tried to up load the pics of my table but it did not work.
Silver Skeeter (author)  OrchidNight1 year ago
Hey there and thanks for the kinds words! I'm glad to hear that things worked out for you. I'd love to see the pictures of your completed kotatsu. Try imgur.com for free image hosting.

Also, I don't know much about the Cozy Legs heater, but be sure to read the safety manual to double check that there's no safety risk with keeping objects so close to it. I know that traditional space heaters have this stipulated.
Silver Skeeter (author) 1 year ago
It's pretty sturdy without the bottom piece. At least, it's as sturdy as a coffee table made by Ikea can be ;).
where can i buy a custom tabletop in canada, calgary? And is there any online store?
Silver Skeeter (author)  sushiwasabi1 year ago
Sorry, I don't live in Canada so I'm unable to help you. Good luck!
You can buy a kotatsu from the online japanese grocery store marukai. or just the heater. if they are out, which they usually are, call them. they have great customer service and are willing to do phone orders. another place online that sells the tables and heaters is Jlist.
kderusha2 years ago
Just so you know, BeNippon is shut down, sadly. It seems eBay and local Asian furniture stores are the only way to obtain a kotatsu heater anymore.
Silver Skeeter (author)  kderusha2 years ago
I didn't know that! Thanks for the info.
Frederbee2 years ago
I built my own kotatsu in Canada, and I ordered a heater from the US called a cozy legs heater. It was designed to mount to the back of a desk, to save money heating office buildings (since the heat rises up and only heats the employee, not the room). It's electric, solid panel, doesn't get too hot to touch with your bare knees, and heats up the under the table area in about 10-15 minutes. It does not require air flow, as it functions much like a heating pad/blanket. It's expensive, but SO worth it n.n My winter here was -40C most of the time, and it costs me a lot to heat my house so I stick to this and keep the thermostat down low
Jaie3 years ago
I've wanted to build one for years and have researched them pretty throughly.

I think it is great if more Americans start using them, lots of other countries (including in the middle east) use some method using a table, and blanket and heater. I'm in Upstate NY where in February, you can have the heat on 80 and still feel cold.

And I've even debated using an Ikea table. (nearest Ikea is 5 hours) my biggest concern with your design is that in most traditional designs even for the Iranian tables, these are called korsi, btw, you have ventilation. In the Japanese tables I've seen, the main table is open at the top and the top sits on just as you have it in your picture, on top of the blanket in winter, exposed in less cold seasons. Now, obviously back in the old days when the heaters used coal and kerosene you wanted air flow, but with electric heaters you also need some air flow. Not just to prevent a fire but because you could burn out the motor in the fan from overheating. Easily done if you don't have any additional air circulating.


Have you used it a full winter yet? I'm curious if someone using this table doesn't feel the need to get up and turn the heat up "just a little more" if they are warm enough under the table.

And you need your bowl of oranges ;)
Silver Skeeter (author)  Jaie3 years ago
Do you have any links to photos of kotatsu with this ventilation? When I was in Japan, I don't remember seeing any ventilation.

That said, I primarily use it in the winter when I have friends over. I start it on high but eventually end up having to turn it to the lowest setting because it gets incredibly warm underneath the blanket. That takes about 10 minutes.

If Ikea is not an option, you can take any table and convert it to a kotatsu using the same steps -- you'll just need to obtain an additional piece for the countertop.

Good luck and let me know if you have any more questions!
frodo693 years ago
I live in Australia, what kind of step-down voltage transformer would I need?
Silver Skeeter (author)  frodo693 years ago
From this site (http://www.adaptelec.com/index.php?main_page=document_general_info&products_id=237), it says that Australia uses 240V. You would need a 240V to 100V step-down transformer.
I love Instructibles! I was watching an Anime and saw the characters referring to the Kotatsu. When I realized what it was, I had to have one. After trying too find one to buy, I found they were WAY over priced and available only from Japan.

I'm now building one for myself. Thanks for the tips on sourcing the Heater unit!
Silver Skeeter (author)  Giesterfarher3 years ago
Good luck! It's really quite easy. Let me know if you have any questions.