• Why build an electrically heated table?
• The table
  • Step 1: Get a table
• Heating the table
  • Step 2: Choose a heat source
  • Step 3: Choose a thermostat
  • Step 4: Wire everything together
  • Step 5: Program the thermostat
• Insulating the table
  • Step 6: Insulate the heat foil
  • Step 7: Get a carpet
  • Step 8: Find the blankets
• Dressing and undressing the table
• Safety

Why build an electrically heated table?

For centuries, many cultures have used heated tables for thermal comfort in cold weather. Examples are the “kotatsu” in Japan, the “korsi” in the Middle East, and the “brasero de picon” in Spain. A heat source goes under a table, a blanket goes over it, and people slide their legs underneath. The micro-climate under the blanket keeps you comfortable, even though the space in which you find yourself is cold.

The heated table is an excellent example of our ancestors’ energy-efficient way of warming: heating people, not spaces. Historically, glowing charcoal from the fireplace heated the space under the table. While that provided sufficient warmth, it also carried a significant risk of fire and carbon monoxide poisoning. Nowadays, we can use electric heating technology instead. For example, the Japanese kotatsu is still in use, but it’s now working with a small electric heater fixed under the table surface.

In this manual, I will walk you through the making of an electrically heated work desk for one person. I have built the table for myself in the co-working space in Barcelona where I have my office now. The building, an old industrial warehouse, has very high ceilings, no insulation, and little sun in winter. It can get very cold here and conventional heating systems don’t work. My heated table turns out to be a perfect solution. I can power it with a solar panel, a wind turbine, a bike generator, or a battery. I can also plug it into the power grid.

A heated table offers exceptional comfort. The lower part of your body gets immersed in heat as if you are baking in the sun or sitting in a hot bath. The warmth quickly spreads to the rest of your body through the bloodstream.

During a week of experiments in December 2024, with indoor air temperatures of 12-14°C (53-57°F), I recorded very low energy use for my freshly built heated table: between 50 and 75 watts per hour. ¹ Compare that to a conventional electric portable heater, which easily consumes 1,500 watts per hour (and does not guarantee thermal comfort). My heated table uses as little electricity as charging a laptop or heating two liters of water for a hot water bottle (58 watts per hour, assuming you reheat the water every two hours).

It takes about 15 minutes before the heat effect of the table becomes noticeable, one hour before it heats at full power, and two hours before it reaches its maximum energy efficiency. Energy use drops from 75 watt-hours in the first hour to between 50 and 60 watt-hours in the third hour, as the thermostat turns off the heating more often. The system accumulates heat in the carpet, the blankets, the table, and the human body. If you turn it off after three hours, walk away, come back 30 minutes later, and turn it on again, the table is heating at maximum capacity within 10 minutes.

The manual

Building an electrically heated table is quite a simple project, which requires few technical skills and little time. Once you get all the parts together, you can assemble a heated table in a few hours. The costs are limited, too. ² The construction process consists of three parts: wiring the electrical system, programming the thermostat, and getting the textile layers and insulation right.

What you need:

• Table
• Carbon heat film
• Thermostat
• Blankets
• Carpet
• Extra insulation material (I used cork)

Step 1: Get a table

This manual concerns a table for only one person - my writing desk. Unlike the Japanese and Middle Eastern examples, my table is adapted to a Western-style sitting position: not on the floor but on a chair. You can turn any table into a personal heat source, but some are better suited than others. Most importantly, you should be able to screw a flat heating foil (step 2) under the table. However, structural elements may complicate that, as is the case for my table (see the image below).

I solved this by installing the heating foil on a thin wooden board which I then screwed against the supporting elements. However, for some other tables, this may not work. Choose a wooden table. Wood insulates relatively well, so a wooden table top already provides some of the insulation you need to maximize heat production. It’s easy to screw things onto a wooden table as well.

You can build a larger heated table that can seat more people, but in that case, you will have to connect several heating foils (step 2) and stitch several blankets (step 8) together. Low-tech Magazine will build a large heated table for several people during a workshop in Barcelona on January 25, 2025.

Step 2: Choose your heating element

In principle, any electric heating device can power a heated table. However, because a heated and insulated table is so energy efficient, you need an electric heater with a very low power use. The average portable electric heater is way too powerful for our purpose. Due to its high surface temperature, it could also cause burns or provoke a fire when you put it under a table.

Carbon heating film

The best heating element for an electrically heated table - and the one I am using in this manual - is carbon heating film. These very thin heating foils are primarily meant for electric floor and wall heating in buildings and vehicles, for protecting batteries or water tanks against the cold, or for warming beehives and terrariums. Carbon heating films are low-temperature, large-surface heaters, so there’s no risk of burns or fire through direct contact with skin or clothes. They are meant to operate at a maximum temperature of 40-45°C (104-113°F).

Voltage

Carbon heating foils come in different voltages: 12V, 24V, and 110/220V. I chose a 12V heating foil to make my table compatible with my 12V solar installations and bike generator. If you have a 24V renewable power system, choose a 24V heating foil.

If you want to plug the table into a wall socket, using mains power, there are two options. First, you could buy a 110V/220V heating foil, add a compatible plug, and connect it directly to the power socket. However, you really need to know what you are doing, because such high voltages carry the risk of electrocution. A safer DIY option is to use a 12V or 24V heat foil connected to a power adapter that steps down the voltage from 220V to 12 or 24V (comparable to the charger of a laptop). That is how I tested the table because I don’t have solar panels in my new office yet.

Size

Carbon heating film is available in different widths, for example, 20, 30, or 50 cm. You can buy it per running meter, and it’s flexible enough to be rolled up tightly for transport and storage. You can cut the foils to size in length at certain intervals. They have electric cables soldered to the positive and negative terminals, ready to plug into the power source. However, if you cut the foil into pieces, you will need to solder cables to all the new pieces. You can connect carbon heating foils in parallel, operated by only one thermostat (step 3). My table only has one heating foil, cut to size.

Power use

The power use of carbon heating foils - expressed in watts per square meter (W/m2) - varies because of two factors. First, heating foils are sold with different power outputs, mostly between 100 and 250 W/m2. Second, there’s size. If your 1m2 carbon foil reads 130 W/m2 and you cut it in half, then 0.5 square meters of heat foil will demand 65 watts. My table’s carbon heating film has a power use of 220W/m2. I first used 0.375 m2 of heating foil (50x70cm), resulting in a power use of about 82.5 watts. Then I cut off a centimeter to make it fit better under the table, and as a result power use dropped to roughly 75 watts.

Step 3: Choose your thermostat

You should only operate a carbon heating film with a thermostat. Without a thermostat, a heating foil could overheat and get damaged or cause fire. A thermostat also provides a stable comfort zone under the table. The thermostat turns the heater off when it reaches a set maximum temperature, and turns it back on when the temperature drops a few degrees lower.

The thermostat voltage must match the heating film voltage: if you have a 12V heating foil, you need a 12V thermostat. If you have a 24V heating film, get a 24V thermostat. The thermostat I use for my table is the W3230 DC 12V. It’s a widely sold device for all kinds of purposes. You need to wire the thermostat and set the temperature.

Step 4: Wire everything together

The thermostat is connected between the heat foil and the power source, as shown in the illustration below. The wiring may be different for other thermostat models.

Cable size

Your cables must be thick enough for the current that flows through them. Carbon heating foils are sold with thick electric cables included, and they are often much longer than you need them to be. You can cut them shorter and use the rest to wire the whole system. If you want to use other cables, then use a multimeter to measure the current that the heating film draws. For example, my 12V heat foil requires 6.6 Amps, so my cables - in the complete circuit - should have a conductor cross-section of at least 2.63 mm2 (that’s 13 AWG gauge, check this chart).

Fuse

Any electrical system needs fuses for safety. Once you have cut your heating film to size, measure how much current runs through it. Next, install a fuse that is slightly above that value. My table uses 6.6 amps and I added an 8A fuse. Read more about fuses in our solar power manual.

Switch

You can add an off-on switch in your circuit to turn your heated table on and off. Use one that has a light indicator, so that you don’t forget to stop the heating system when you leave. You could also install a motion sensor under the table. That said, if you have wired your system correctly, used the right cable thickness, and added a fuse, leaving it on accidentally will not cause any safety problems.

Temperature sensor

The thermostat comes with a temperature sensor that you should install between the heating foil and the table (touching the heating foil). Make sure to fix this sensor securely, as it is essential to the proper and safe functioning of the heating system.

Where does the thermostat go?

Before you start wiring the system, decide where your thermostat goes, because it will determine the length of the cables you need. I have my thermostat installed under the table, hidden under the blankets. Once programmed, there’s no need to access it regularly (see further). Having the thermostat on top of the table means that you need a hole in your blanket for all the cables to go through. It also complicates the adding and removing of blankets.

Step 5: Program the thermostat

To program the thermostat, connect it to the power source. First, select the “heating” function. My thermostat’s default setting was “cooling” and I struggled to make it work at first. Here’s the steps to follow:

• Press and hold “set” to enter the code setting menu.
• Press up or down to select “P0”.
• Press “set” again to enter the code setting
• Press up or down to select “H”
• Wait 3 seconds and the setting is saved.

Next, you set the temperature at which you want the thermostat to turn the heat foil off. Heat foil manufacturers advise 40-45°C (104-113°F) during sustained use. Here’s what to do:

• Short press “set” and the blue number will start blinking.
• Press up or down to select the maximum temperature you want
• Wait 3 seconds, and the setting is saved.

You can leave all other functions of the thermostat untouched.

Insulating the table

To build a comfortable and energy-efficient heated table, you need to understand that a carbon heating film emits heat on both sides. If you simply attach it under a table it does not get warmer than 30°C, which will not improve thermal comfort in a significant way. It’s only when the heating surpasses skin temperature (around 35°C/95°F) and core body temperature (37°C/99°F) that you start feeling the warmth radiating towards you.

To reach sufficiently high temperatures, you need to cover one side of the heating foil with heat-insulating material.

To reach sufficiently high temperatures, you need to cover one side of the heating foil with heat-insulating material. That will force most of the heat output to the other side - the side that radiates energy towards your body. The carbon heat film for a heated table is placed below the tabletop, radiating heat downwards, and so the insulation goes on top. ³ It consists of the wood table top, one or more blankets, and any additional insulation material that you add to the table surface.

When carbon heating films are used as floor heating, the insulation is below. The upper side needs to be protected by a material that is strong and easily radiates heat, such as ceramic tile. However, when you build an electrically heated table with the foil radiating heat downwards, there’s no need to protect the exposed side. It can be touched safely and nobody is walking on it.

Step 6: Insulate the heat foil

To improve the heat output of the carbon film, I have added 3 cm of cork insulation in the space between the carbon film and the table surface. I have not done any tests without the cork layer, but I am confident that the energy efficiency and thermal comfort of my table would not have been so excellent if it would not have been there. Other suitable natural insulation materials are wool, cellulose, wood fibers, hemp, and flax. You could also try radiator heat reflector foil.

Step 7: Get a carpet

If you put an electrically heated table on a cold floor, you will not be comfortable. The cold floor will suck up all the heat from the carbon heat foil, and your feet will conduct warmth to the floor. You need to insulate the floor, and you can do that with a wool carpet (or several wool carpets on top of each other). New wool carpets are expensive, but they don’t need to be much larger than the table and they can be found cheap second-hand. I got the very large Persian-style wool rug in my office for 50 euros, and I will add a second one on top to further improve the floor insulation.

Step 8: Find your blankets

The energy efficiency and thermal comfort of an electrically heated table are in large part determined by the type and size of the blankets you put over it. The blankets form part of the heat film insulation layer, but if they are long enough to reach the ground they also insulate the space under the table.

Radiant heating systems transfer energy to surfaces - including your body - and do not warm up the air directly. However, the air temperature under the table will slowly increase indirectly due to the higher surface temperatures of the blankets, the table, the carpet, and the person who sits at the table. During the experiments, the air temperature below my table at 25 cm above the floor increased by about 10°C (18°F).

Wool

Choose a wool blanket. Wool traps heat very efficienctly, is much more flame-resistant than other textile materials, doesn’t get dirty or smelly easily, regulates humidity, and purifies the air. ⁴ New wool blankets can be pricey at hundreds of euros for the size we need. However, I purchased four second-hand wool blankets for 90 euros, two of them large enough to reach the ground. If you find a wool blanket that is ugly or stained, simply layer it with a nicer and cheaper cotton blanket.

Blanket size

The size of the blanket you need depends on the size of your table (length, width, height). My table measures 80 cm long, 56 cm wide, and 75 cm high. That means that my blanket should measure at least 230 cm (75+80+75cm) x 206 cm (75+56+75cm) to reach the ground. Can’t find a blanket that is large enough? You could build a lower heated table and sit on the ground, or you could sew several smaller blankets together. Smaller blankets can also be useful in combination with larger blankets, or they can serve as the only blanket when it’s not so cold (see further).

Work surface

Although it feels nice to work on a wool or cotton surface in winter, you can also put a wooden board on top of the blanket, cut to size, in order to protect the blanket from wear and dirt. Or, you drape a cotton tablecloth over the blanket, which is easier to wash than wool.

Dressing and undressing the table

Any heating system must be able to adapt to varying temperatures. For a central heating system, that happens by manipulating the thermostat. However, that doesn’t work so well for a heated table, because the temperature range of the carbon heating film is limited. Going below 38°C (100°F) will not provide a pleasant sensation of warmth, while prolonged heating above 45°C (113°F) may damage the heating film and make it too hot to touch. However, you can adjust thermal comfort in a wide range of air temperatures by “dressing” and “undressing” the table: by adding and removing textile layers, and by using them in different ways.

You can adjust thermal comfort in a wide range of air temperatures by adding and removing textile layers, and by using them in different ways

It’s not an exaggeration to say that the blanket becomes part of your clothing. Sitting at the table feels like wearing a very large dress that is heated from the inside. Just like we dress differently depending on the weather, adding and removing layers, the number of blankets, and how they are positioned can reflect the environmental conditions. I have tested the table with one to four blankets, and with every extra blanket energy efficiency and thermal comfort increase. On a very cold day, you could add two or three blankets hanging down the table. If you are still cold, you could drape extra blankets over your chair and shoulders. You could end up in a complete tent, heated from the inside, with just your head and arms sticking out.

However, as you add more blankets, the textile layer becomes increasingly heavy, and it takes more time to get in and out - to “dress” and “undress”. Consequently, a lighter cover is preferable if it provides sufficient comfort. On a chilly spring evening, one or two shorter blankets may be sufficient to keep you comfortable. I have tested the table like that and it did almost as good as with a large blanket. Energy use was somewhat higher and thermal comfort somewhat lower - I especially noted cold feet. However, should it be a bit warmer, I would prefer this setup because it’s more practical to get up from the desk.

Overheating can be solved without reaching for the thermostat as well: lift a corner of the carpet with your foot and let some heat escape, or remove one of the blankets. It would be more energy-efficient to turn down the thermostat, but the energy use of a heated table is already so low that there is room for some convenience. The comfort of a heated table can be further improved by a heated chair or bench, or by putting a screen behind your chair, covered with heat foil on one side and with insulation on the other side. That’s something for a future manual.

Safety

While an electrically heated table is much safer than a table heated by fire, it does entail some risks, including a fire. However, this can only happen when you ignore some crucial rules, which I repeat below:

• Never operate a heat foil without a thermostat.
• Make sure your electric cables are thick enough.
• Add a fuse to your electrical system.
• Fix the temperature sensor securely: it should always stay in place.
• Avoid blankets and carpets made of synthetic fibers, which are highly flammable. Your heated table won’t catch fire if you follow the advice above, but a fire can start elsewhere in the space. The best material for blankets and carpets is wool, which does not catch fire. Cotton is flammable, but it’s not as bad as synthetic material.
• Long blankets are more energy efficient than shorter blankets. However, watch out with too long blankets because they can make you trip when you get in or out of the table.

Colophon

Heated table: Kris De Decker.

Illustrations: Marie Verdeil.

Photos: Marina Kálcheva.

Model: Anita Filippova.

Photoshoot location: AkashaHub Barcelona. Thanks to Carmen Tanaka.

Marie Verdeil and Roel Roscam Abbing gave feedback on the draft of this article.

Related DIY Manuals:

• How to build a small solar power system
• How to build a practical bike generator

Relevant books:

• Heating people, not spaces.