How to save on the heating bill AND stay warm – build a Kotatsu table!

Brr… Winter is almost here. The overnight temperature plunged into the 30s a few times recently. This seems a bit early to me. Usually, it doesn’t get this cold in Portland until December. The weather is strange this year. It’s been a lot drier than usual. The crisp sunny days are beautiful, but this also means it’s colder. I’m not exactly sure how it works, but it isn’t as cold when we have some cloud cover or rain. It’s actually really great to have all these sunny days in October and November. I don’t think we’ve had a dry autumn like this in a long time. Anyway, it’s cold now and it’s time to convert our coffee table into a kotatsu table. Yes, I do this to save some money on the heating bill, but it is really cozy too.

Ahhh…. I love our kotatsu table. It’s so warm and toasty. We have been using our kotatsu table since 2003 and it is still awesome! There is nothing better than warming up at the flick of a switch when you come in from the cold. The kotatsu table is our favorite winter appliance, by far. It’s easy to DIY and it will pay for itself in the long run. I highly recommend investing a little time and building one for yourself.

*Disclaimer: You should not leave any heating device unattended. We haven’t had any problem, but everyone needs to be safe and pay close attention to your heaters. You should turn it off when you’re done. I take no responsibility for and will not be liable for anything you build. We may receive a referral fee if you purchase something from Amazon through the links in this post.

*This post was originally written in 2010. I update it every few years with the latest info. It’s much easier to buy a kotatsu table now that Amazon has grown so much.

How to build a kotatsu table

Staying warm AND save money

It’s about this time of year that all the personal finance magazines and blogs come out with articles on how to save money on heating. The usual advice to is to turn the thermostat way down and bundle up. This is good for the wallet, but it doesn’t work for us because Mrs. RB40, my wife, hates being cold. Luckily, I have a secret weapon. Our kotatsu table is the key to staying toasty and keeping our heating bill low.

We lived in a condo and we don’t have gas. The heating and cooling system ran on electricity which is more expensive than gas. Our monthly electric bill averaged around $60 in the warmer months and around $100 in the winter. We generally kept the temperature around 68 degrees with 2 space heaters and rely on our kotatsu table to warm up. Here is our energy usage from 2016 to 2018. *We moved into a house in 2019 and don’t have 2 years of record yet.

electricity usage

If you’re looking for a space heater, you can’t go wrong with the DeLonghi oiled filled radiant heater. It worked great for us.

What is a Kotatsu Table?

What is a kotatsu table exactly? A kotatsu table is basically a covered coffee table with a heating element underneath. It’s hard to describe the cozy comfort if you haven’t experienced it. Napping under the kotatsu table is heavenly. Trust me, it’s one of the best feelings in the winter.

I’m not sure where I first learned about the kotatsu table. I must have seen it in a Japanese manga or anime when I was a kid. The kotatsu table is very common there and every household has one. Many Japanese homes are not insulated well and the kotatsu table is an economical way to stay warm. Why heat the whole house? It’s much cheaper to heat your own personal space.

You could buy a kotatsu table on eBay or Amazon for $150-400, but that has some drawbacks. They used to have a high shipping cost because most kotatsu tables are shipped in from Japan. A few years ago, you could only find them on eBay. Now, you can get it on Amazon with free shipping! That’s awesome. It’s a lot more affordable now. However, there is still another problem.

One issue is that the kotatsu tables are generally pretty small. The usual tabletop size is 31×31 inches (80 cm) and most are only 14 inches high. This is too short if you’re tall. We purchased our first kotatsu table at a Japanese store in CA for about $130. After a few years, I decided to build a bigger and taller table because we wanted more space. Our DIY kotatsu table is a lot more comfortable now with more legroom. It is about 18” high. The 4 extra inches makes a huge difference.

This small kotatsu table at Amazon looks exactly like the one we first purchased. It’s not too expensive at $225. The size is 30” x 30”. I’d go for this one if you don’t want to build your own. It’s a bit short though at 14” high. (This item was $168 in 2018.)

small kotatsu table

Here is a nicer looking kotatsu table at Amazon for about $395. The height is still 14 inches, though. The tabletop is 36” x 20”. Unfortunately, that’s a bit too narrow for us. We need more space.

small kotatsu table

Build your own kotatsu table

What you need

  • A Coffee table – You need to find a coffee table with two top surfaces.  The LACK Coffee table from IKEA is perfect for this. It’s $50 from IKEA. The dimension is just about perfect – 46″x30″x18″. There is a smaller version that’s 35″x21″ as well. Alternatively, you could get 2 coffee tables from Amazon. Then, you’ll have two tops to use.

LACK coffee table kotatsu table DIY

  • kotatsu table heating elementA heating element – You can buy a “kotatsu heater” on Amazon or eBay. They used to charge $30 shipping in 2011, but now there are many free shipping options. I tried other heating alternatives, but they don’t work that well for this purpose. For example, a small space heater seems dangerous. The kotatsu heater element is designed specifically for this use and it’s less expensive now. I wouldn’t cheap out on this. Here is one on Amazon for $105. (The price increased quite a bit recently.)
  • $0 old king size blanket/comforter – We have plenty of spare blankets so this didn’t cost us anything. I like the king-size, but a queen would work too.
  • A 120 V to 100 V voltage transformer rated at 500W – You can get this transformer from Amazon for about $35. (*You need at least 500W.) North American outlets put out 120 V but Japanese appliances run on 100 V. The heating element will run a bit hot if you don’t use a step-down transformer. We don’t have a transformer and we only use the heater on the lowest setting. If you crank up the setting, it could overheat. The transformer is nice insurance if you have curious kids around.
  • Optional: Pillows to sit on.  You can also pick up some big pillows from IKEA while you’re there. It’s a lot more comfortable than just sitting on the carpet. Another good alternative is to get some floor chairs from Amazon. Check it out. This looks pretty comfortable. However, this floor chair is not cheap at $50.

floor chair

  • belkin power switch$10 power switch – Our heating element doesn’t have a switch so I got a power switch for it. It’s a lot easier to turn on and off than physically pulling the plug every time.
  • Corner braces – You can get these small corner braces from any hardware store. You probably should wait for the heating element to arrive so you’ll know what size to get.

Putting it together

Putting together the kotatsu table is really easy. You probably don’t even need instructions, but here they are anyway.

  1. Put the LACK coffee table together per IKEA’s instructions. Leave the lower shelf out for now.
  2. Mount the heater. I screwed our heating element right into the bottom of the coffee table. You can attach it with 4 corner braces as well. Or you can build a frame as pictured below. The mounting holes are on the side of the unit as you can see from the image.kotatsu table DIY build
  3. Throw the big blanket on top of the LACK coffee table.
  4. Put the bottom shelf (or another tabletop) on top of the blanket.
  5. Voila, you’ve got a kotatsu table!

If you can sit on the floor comfortably, you will love the kotatsu table. It is super comfortable and we don’t have to set our HVAC very high. We usually set the temperature at 70 degrees and that’s enough with the kotatsu table as a supplement. Our son really likes hanging out at the table as well. Oh, a side benefit is that it forces the family to hang out in the same area. We’ll play plenty of board games this winter.

Happy DIYing! How do you keep your heating bill down?

More on how to stay warm! – 10 Unconventional Ways to Save Money on the Heating Bill.

 

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Joe started Retire by 40 in 2010 to figure out how to retire early. After 16 years of investing and saving, he achieved financial independence and retired at 38.

Passive income is the key to early retirement. This year, Joe is investing in commercial real estate with CrowdStreet. They have many projects across the USA so check them out!

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74 thoughts on “How to save on the heating bill AND stay warm – build a Kotatsu table!”

  1. I’m not sure if this will be answered because I’m not sure about how old this actually is but I was wondering I clicked on the link to the heater that you had linked and it’s much more expensive now well not that much it’s about $104 now but it says that the dimensions are 29 in and I believe the dimension on the table with Wise It’s only 30 in does that fit in there then? Because in the drawing shown or the picture shown it looks like the heater is much smaller than the table?

    Reply
  2. A real kotatsu table has an infrared heater underneath it. I spent 9 years in Japan and I think they are wonderful for organizing, reading and board game playing. The table itself is built so that the sunken living room floor underneath accomodates about 12~15 inches of leg space so it comfortably lets you sit on a pad and watch tv while sipping tea and chatting. If you have the money, try laying out tattami mats in a room with a window and a koi pond out back. This is the essence of Japanese style of living and the reason most Japanese people are homebodies…it’s feng shui, quiet living and it can really change you’re perspective on living comfortably and elegantly in style…it’s fun to go out and do the town a couple times a month, but when you come back home you ought to be living you’re best life !

    Cheers !

    @@ Cat… :”>

    Reply
  3. In Spain (Europe) we have been using this forever, but the table is normal height, much more practical. The heating device is a small, flat electric appliance that uses little energy (in the past hot coals were used).
    The table is called ‘mesa camilla’ and the heating device ‘brasero eléctrico’. Very cheap and efficient way to stay warm while sitting!

    Reply
    • That’s really cool! I’ve never heard of the Spanish version.
      I’ve been thinking about this for a long time. How do you keep the heat in once you sit down with a chair?
      There would be a big hole under your seat and all the heat would escape.
      Do you put a blanket over the chair or something like that?

      Reply
      • You can cover the back of the chair with a blanquet or a coat, but most people do not bother, the heat loss is not too big as heat tends to go upwards. The surface of the table gets warm, so your hands and arms are sufficiently warm and you can eat, read and use your laptop and be very confortable. The heater sits on the floor and typically has two settings: 400W and 800 W, no fan. Usually 400W is used.

        Reply
  4. I have come to know about kotatsu when I visit the Japan 5 year ago. Since that, I start searching the kotatsu table in America and finally found a big collection of kotatsu table and related furniture online. There are very few online store from where you can buy the kotatsu table

    Reply
  5. When I was reading the post, I was imagining the fire risk, but nothing has come up in the comments. However, if there was an issue, I wonder how an insurer would view it and whether they’d try to get out of any claim?
    The new place we’re getting has underfloor heating, which is a first for me. I’m looking forward to see how that feels.

    Reply
  6. I just made this table! It’s so nice and high. It’s the perfect height for me. The lack table came with L shaped brackets so I didn’t even need to buy those! Thanks for the detailed instructions! I couldn’t be happier.

    Reply
    • That’s great! I love our kotatsu table. We’ve used it for over 10 years now and I can’t live without it in the winter.
      Great job building one. The height is much better than the kotatsu table from Japan. They are too short.

      Reply
  7. Oh my I never thought of this as a cost saver!!! It’s like building your own fruit/jerky dehydrator underneath the table. Part of me want a big house with a gate (confession…) but I definitely do not want it enough to try to heat it up every winter.

    Reply
    • Big houses have their charms.

      Personally I reaaaally want a traditional Chinese Siheyuan.

      But a big house that wasn’t divided into functional areas that are thermally isolated would be a nightmare for anyone who doesn’t absolutely need the space.

      Reply
  8. I used this article as a reference to build my own kotatsu, and now that it’s done, I figured it’d be worth reiterating the importance of some of Joe’s points, as well as address some concerns that others have expressed (and that I had too before building one).

    — “We also tried the “cozy legs.” It didn’t heat up enough for us.”

    Seriously, this. This is not the way to go. It’s only 150 watts, which simply isn’t enough. You can buy a kotatsu heater from 300 – 600 watts that will actually put out heat. On top of that, the Cozy Legs heater that others have used has been discontinued, so if it breaks, you’re out of luck.

    — The Belkin power switch is a good idea, but you may or may not need one depending on the model of your heater. Mine came with a switch, otherwise I would have gotten one.

    — A lot of people are worried about fire safety. The “back side” of the heater faces the exposed particleboard, which, to an extent, is fire resistant already. I used a different table, but if you’re still concerned, you can do what I did and add a thin piece of hardboard panel between the heater and table top (it’s pretty straightforward, but here’s the guide I wrote if it helps: https://japanesefutonzen.com/diy-kotatsu/).

    Can’t comment yet if it has saved me money on my utility bill. We’ll see next month 🙂

    Hope this helps others, and thanks for the inspiration!

    Reply
  9. Hi Joe,

    thanks for this neat guide. Will try my way with it, will need to do a few adaptions though due to different electricity standards here in Europe but your article defintely helps.

    Building them yourself is just the better option compared to importing it.

    Best
    Martin

    Reply
  10. I just bought a Kotatsu heater from Rakuten. The heater itself is ~$16 usd plus ~$35 shipping. The unit arrived in one week. It works fine. My house temperature is around 65 degree, but I feel very cozy under the table with my short. There is only one problem. The top part of the heater can get pretty hot. I may be completely wrong, but I think it’s better to leave some space between the heater and the table when you install it on a Ikea table.

    Reply
  11. Thanks for this great article! Though I am aiming to retire by 40 and really love the blog for the personal finance tips, I’m pretty sure this was the first article I read. I constructed a kotatsu and it has been fantastic! I’m not really sure whether it has saved us much money, as all three of my roommates tend to favor more heating than I do in winter. But I compromise a bit because they’re all awesome.

    When I lived in Japan, the kotatsu was wonderful as a center of family life. But yeah, the insulation was pretty terrible. It was amazing how warm and cuddly you could be, though, just by taking a super hot bath, having some kotatsu time, then snuggling up underneath a bunch of blankets. I am going back for a visit this winter and can’t wait!

    Reply
  12. Joe,

    Interesting stuff. Never heard of it before, but that’s pretty unique. I know it can get pretty cool/wet there in Portland for more than half the year, so it’s awesome you guys found a way to reduce the heating expenses down somewhat.

    “Happy building! How do you keep your heating bill down?”

    My answer to that question is living in a tropical climate. Practically no heating bills here in Florida. Keeping the A/C near almost 80 year round means it’s pretty comfortable in the apartment with minimal HVAC expenses. I think we spent like $75 on electricity last month. Works for me. 🙂

    Cheers!

    Reply
    • It’s cold in the winter, but not bad in the spring and fall. I think you would be able to handle it. The people with the most problem are stuck in the office from 9 to 5. It’s not so bad when you can be outside once in a while.
      I like your answer. I’m sure I’ll end up in a tropical zone eventually.

      Reply
  13. “Most Japanese housing are not insulated well and the kotatsu table is an inexpensive way to stay warm.”

    This sums it up. Having lived in Japan for 9 years I can say that Japan is generally clueless about insulation, and the Kotatsu is the “poor man’s” answer to a bigger problem I’m pretty sure it’s inefficient if you look at the overall numbers, unless you like to have your house freezing cold except for a 1sq meter area. If you really have a problem with heat in your house, the real solution is to improve insulation and fix your central heating.

    A Kotatsu in itself is great, but good luck when you want to start working on your computer at your desk, because then you’ll be freezing.

    Our Electricity bill was twice as big in Japan as it is in the US, by the way ( http://howtoretireearly.net/a-comparison-of-the-cost-of-living-in-japan-and-the-us/ ). Terrible insulation does that to you.

    The kotatsu itself is a nice piece of appliance, but it’s sad that it is considered as the “right” solution to heating expenses, when it clearly is not.

    Great DIY post, nonetheless!

    Reply
    • You’re right. The real solution is to improve the insulation. Our building is very well insulated and we get radiant heat from the units around us. Thanks for the link. It’s interesting to see the cost of living comparison. I’d love to live in Japan for a while.

      Reply
  14. hi Joe:

    wow, your indoor temperature is 64 degrees. That is amazing your kid and wife are ok at that temperature. For me at 68 degrees I already feel cold. We usually set ours around 69 to 70. and I thought that was being really economical. But still my gas bill is around $300 or so in the worst of winter. I also live in Portland.

    I have learned that by bundling up with extra layers of clothing. I usually have about three layers. That does the trick for and it works better for me though.
    I don’t feel as cold, and I don’t need to set the heat so high.

    Just a suggestion…

    My family needs at least a minimum of 68. especially my mom when she comes over to visit.

    Reply
    • That’s whey we spent so much time under the kotatsu table… Actually, I have been turning it up the last few years. The 64 degree was in 2010. I usually keep it at 68 now. 🙂

      Reply
  15. This would be perfect for Mrs. Root of Good. I like it cold but this thing could keep her (and the kids!) warm.

    I’d just be concerned about the kids knocking it over and starting a fire.

    Reply
    • Once you attached the heating element to the coffee table, it’s pretty much impossible to knock it over. You should try it.

      Reply
  16. I’m with Mrs. RB40 on always feeling cold. Best tips are-wear several layers around the house. Now thermal base layers (thermal underwear) is made from polar fleece. This fabric is made from plastic (soda bottles!) and is one of the warmest. A few layers of clothing makes a huge difference. Wear a hat from this fabric (or wool) around the house, who cares what you look like! And sox, especially w/a bit of wool, like 5-10% makes a huge difference.
    I read that thermal window covers are one of the most effective ways to keep heat in, cold out. You could switch them out in the summer months.
    Fleece and down comforters are on all chairs and the sofa for use. The dogs even have their own.
    My best find lately is a small heater, the size of a shoebox, for $10 from Walmart. It is not recommended for bathrooms, but I’m super careful w/it and that’s exactly where I use it! Heats up in seconds for when you step out of the bath or shower, instead of heating up the whole house. It’s also cool to the touch. As long as you follow the instructions in the manual, this little heater is fantastic. The polar fleece thermal base layers are from Walmart too. Save your hard earned cash for more important things-like tropical vacations!

    Reply
  17. I wouldn’t try to save money on the heating element. I would buy a reliable element. You can probably buy from Ebay and AliExpress cheap elements, but you should look for a higher standart elements.

    Reply
  18. “How do you keep your heating bill down?”

    I don’t do much except close the heat vents in the rooms downstairs that I don’t use and open the drapes fully when the sun is shining through by south windows. Having said that, if it gets too cool for me I turn the heat up. When I was younger, I used to turn down the heat at night so much that when I woke up in the morning it was so cold I could see my breath. Not so anymore. That’s craziness. I am too prosperous to that anymore.

    Coincidentally, for anyone interested, in the last five minutes I came across this article about 9 Sneaky Ways to Cut Down the Heat Bills in Your Home:

    https://ca.news.yahoo.com/photos/9-sneaky-ways-cut-home-slideshow-050120463/9-sneaky-ways-cut-home-heating-bills-photo-050120894.html

    Reply
    • I’m glad it doesn’t get that cold around here. 🙂 It’s amazing what we could handle when we were young. Thanks for the article. There are some easy tips there.

      Reply
  19. We don’t have a kotatsu but we do use yutampo (Japanese hot water bottle) to warm our beds here in Japan. Yutampo is far better for one’s health — than an electric blanket, for example. One winter we went skiing in the Japanese alps at Nagano and the Inn had kotatsu for each room but no heating. So we were forced to sleep under the kotatsu — a bit dangerous in my opinion due to fire potential and health reasons, however, it was preferable to freezing to death those nights!

    Our homes here have electric flooring but it is too expensive to use often and I object to it for health reasons, as with the electric blanket or electric heating pad for pets. Electric ‘hot carpets’ are also popular here, but again, I do not think it is wise to expose one’s body to electrical current all winter long.

    Reply
    • The Yutampo is a great idea. I will keep a look out for it. Mrs. RB40 uses a heat pack thing she warms up in the microwave. That works pretty well too, but it doesn’t last long.

      Reply
  20. I wonder if you could get the heat from a dog bed heater instead of the heater you show in the picture. They’re cheaper and they look like they don’t use much power, or overheat.

    Reply
  21. How do you use the table? When you “spend a lot of time under the kotatsu table” are you literally under the table, like it’s a kid’s fort? Or do you just stick your legs under there? Does it provide warmth if you’re just sitting next to it, or if you’re sitting on a couch and maybe just putting your feet underneath?

    Reply
    • It’s best to sit on the floor and stick your legs under the table then pull the blanket over your waist. It works great and warm your whole lower body!
      You can sit on the couch and stick your feet underneath too, but it is not as warm then. Sitting next to it is no good.

      Reply
  22. Sometimes it’s cozier to have a warm spot like this than to heat the whole house – like how nice it is to snuggle under blankets when it’s cold. If the whole house is heated, then most of that warm air is not being used, PLUS can make all the air in the house even drier than winter air usually is.

    Thanks for the tips on making your own!

    Reply
    • In our old house, we warmed the bedroom at night with a space heater and use the kotatsu table in the living room. The room temp was around low 60s and it worked quite well.

      Reply
  23. It does look really nice. I intially had the same question as Little House though.

    I think it is always good to rethink conventional wisdom, and since your November heating bill was only $10 more than the summer, that’s speaks volumes.

    Reply
  24. We have a sun-room (other areas of the country might call them three-season rooms) and it’s gotten pretty cold at night the last month or so. We were looking at a cheap way to heat it since if we leave the door open the thin walls will radiate all of our heat away, haha.

    How hot does a kotatsu get? Is it so hot I have to be careful what type of wood I purchase on the table? Think it would be good in a 14×15 sun-room with tile floors… or is it the space heater for us?

    Reply
    • My heater element is pretty hot, but I don’t think it can reach wood’s combustion point. The LACK table is made of particle boards and I haven’t had any problem yet. I don’t know about sitting on tile floors. It doesn’t sound comfortable…

      Reply
  25. Those tables sound really great on a cold day. However, on the DIY version, how do you make sure the heater doesn’t catch the table on fire? I’m a stickler about fire safety (my step-dad was a fireman).

    Reply
    • I try my best to not leave it on when I’m not using it. If your legs are next to the heater, you’d know when it gets too hot. From what I understand, the ceramic heater element is not supposed to catch fire, but the risk is always there with any electronic heater.

      Reply
      • An authentic kotatsu heater does not heat up like a space heater, it wont light the wood on fire. But it is possible if the blanket isn’t flame retardant that if someone was to physically put it into the heater and hold it there it could catch on fire, but you would have to purposefully do it.

        Reply
    • My worry exactly. All my heating appliances come with warnings NOT to get them covered at all. I assume that, if done right, the table can be safe (and also, if not left unattended).

      To answer the main question: we don’t make efforts to reduce our heating bill. We come from 30 years of Communism here and I still remember, as kid, how cold the apartment was, because we’d get heat few hours a day (same with warm water, it was never too hot anyway :)).

      I have an aversion to cold, so we crank up the heating system and enjoy it. We all wear t-shirts during winter at home and there’s no one that could convince me to go through any more day in cold at home, even if it meant I’d save money for a space rocket 😀

      Reply

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