The Meseta Central is a vast plateau in the heart of Spain with long, cold winters and short, scorching summers. The locals say that there’s “nine months of winter” and “three months of hell”. The region has little trees, so heating (and cooling) has always been a challenge.

In the early middle ages, the Castillians developed a subterranean heating system that’s a descendent of the Roman hypocaust: the “gloria”. Due to its slow rate of combustion, the gloria allowed people to use smaller fuels such as hay and twigs instead of firewood.

The Gloria

Remarkably, the gloria is alive and kicking. Several villages, especially in the wider region around Burgos, still have houses with subterranean fireplaces of which some are in working order.

In January, my friend Pedro took me to his uncle’s house in Hontangas, a tiny village at some 100 km from Burgos. The uncle, now in his late sixties, fires the gloria once every morning during the “nine months of winter”.

A gloria heats one or at most two different rooms, usually kitchen and/or living room. The firebox is located outside the house, often in a courtyard but sometimes on the street. The wall above it is black from soot. The chimney is on the other side of the heated room.

The warm exhaust gases from the combustion heat are led through one or more ducts  that run under the floor of the heated room(s), and then rise through the chimney. The floor and the walls slowly radiate this heat into the room. In summer, a natural air current in the gloria cools the room(s).

The expression “estar en la gloria” (to be inside the gloria), meaning that someone feels happy and comfortable, refers to this medieval heating system.

The obvious downside of the gloria is that you have to get outside in the cold to “turn on” the heating, first thing in the morning. This takes about 20 minutes. Vine cuttings are added first, followed by some firewood.

When the fire is burning well, the firebox is covered with a some metal plates to slow the combustion rate and keep the heat inside. One firing suffices for a day of warmth.

The gloria is related not only to the hypocaust but also to the Korean ondol and the American “crimean oven“.

Friends and readers keep sending me links to a “low-tech” heating system in which tea candles heat a combination of ceramic flower pots. It seems you all need a course in thermodynamics, so let’s start with some basics:

1. First law of thermodynamics: you can’t create energy out of nothing, (and you can’t destroy it). This means that placing two ceramic pots on top of four candles does not increase heat production. You get the same amount of heat if you burn four candles without the pots.

2. Now imagine heating your room with four tea candles.

3. Get more tea candles. One tea candle can produce around 30 watts of heat, which means that you need at least 20 to 30 tea candles to heat a very small room (and replace them every 3 to 4 hours).

4. You have now built a small fireplace using tea candles. However, it isn’t running on wood but on petroleum — the stuff paraffin is usually made of. And above all,  you have built a fireplace without a chimney. Chimneyless fireplaces are very efficient, but they’re not so healthy and that’s exactly why the chimney was invented. Connecting your tea candle fireplace to a chimney will solve the indoor air pollution issue, but unfortunately 85-90% of the heat will then escape through the chimney. So you need more candles.

5. Forget tea candles, get some thermal underwear.

“Early shelters were built of availale materials. Hides spread over poles or the bones and tusks of mammoths formed a type widely used. Stone and clay were common early building materials. Usually there was only a single room, with the fire located at the center of the living area. In many parts of the world this pattern changed little from the earlies times right up to the present. Smoke escaped from such dwellings as it could, through the low door or a smoke hole in the roof… The Scots developed a special word, snighe, for rain that worked its way through the roof sods and dripped down black with soot upon the people below.”

“Today the term stove refers to a certain kind of container for fire; the stove warms the room. In earlier times stove meant the heated room itself… The dwelling was a container for the fire that burned on the open floor. A hole in the roof let the smoke out. The door admitted air for combustion, just as the adjustable air inlet does today on the door of an iron stove… The beehive houses of Scotland’s Western Isles, and the central-hearth houses of Ireland, normally had two doors. Whichever door lay on the side away from the wind was used to adjust the draft. American Indians did much the same with their tipis, lifting the skins on one side as a draft adjustment for the fire that lay on the open floor.”

“Sometimes, as in Scandinavia, there was a louver in the roof, a kind of trapdoor that could be closed and opened with a pole. During the early and smoky stages of the fire the louver was opened. It was closed to keep the heat in after the fire had burned down to charcoal and offered little smoke. In the manors and larger buildings of England, louvers became quite elaborate architectural features. Instead of simple trapdoors, they took the form of cupolas. These blocked the rain but let out the smoke in winter and the heat in summer.”

“The atmosphere in the central-hearth building depended on various factors, including the design of the building, weather, the quality of fuel and its moisture content, and the skill of the firetender. By present-day standards, conditions must have left a good deal to be desired… Still there were real advantages to the chimneyless house. The fire on the floor offers all its heat to the room; it is 100 percent efficient. The chimneyed fireplace offers a meager 10 percent efficiency as a rule, channeling 90 percent of the heat outdoors.”

“The central hearth also saved woodcutting at a time when woodcutting tools were poor. Long sticks could be fed gradually into the fire. And there was room for more people close to the warmth. Many continued to use the open hearth, including some of the colleges of Oxford, long after the chimney became known.”

Quoted from “The Book of Masonry Stoves: Rediscovering an Old Way of Warming“, David Lyle, 1984.

The illustrations are from “The English fireplace: a history of the development of the chimney, chimney-piece and firegrate with their accessories, from the earliest of times to the beginning of the XIXth century“, 1912. It talks about smoke louvers (or smoke turrets) on pages 5-9.

Related: Well-tended fires outperform modern cooking stoves.

“Dr. Charles Tripler, Surgeon and Medical Director of the Army of the Potomac, writes in a letter of November 1861 the following description of “a modification of the Crimean Oven”, devised and put into operation by Surgeon McRuer, the surgeon of General Sedgewick’s Eighth Brigade:

A trench 1 foot wide and 20 inches deep to be dug through the center and length of each tent, to be continued for 3 or 4 feet farther, terminating at one end in a covered oven fire-place and at the other in a chimney. By this arrangement the fire-place and chimney are both on the outside of the tent; the fire-place is made about 2 feet wide and arching; its area gradually lessening until it terminates in a throat at the commencement of the straight trench. This part is covered with brick or stone, laid in mortar or cement; the long trench to be covered with sheet-iron in the same manner. The opposite end to the fire-place terminates in a chimney 6 or 8 feet high; the front of the fire-place to be fitted with a tight movable sheet-iron cover, in which an opening is to be made, with a sliding cover to act as a blower.

By this contrivance a perfect draught may be obtained, and use more cold air admitted within the furnace than just sufficient to consume the wood and generate the amount of heat required, which not only radiates from the exposed surface of the iron plates, but is conducted throughout the ground floor of the tent so as to keep it both warm and dry, making a board floor entirely unnecessary, thereby avoiding the dampness and filth, which unavoidably accumulates in such places.

All noise, smoke, and dust, attendant upon building the fires within the tent are avoided; there are no currents of cold air, and the heat is so equally diffused, that no difference can be perceived between the temperature of each end or side of the tent.”

Read more: 1 / 2 / 3.

Research by the Dutch research institute TNO (Dutch Organization for Applied Scientific Research) shows that contact heating through the wrists is the most efficient way to warm the body — one can turn down the heater 1 to 4 degrees C°. If the undersides of the wrists are warm, the whole body will be warm. By working at a computer, for example, using the mouse, or writing, the wrists are placed on the work top.

The heating elements are integrated into the table top. This is possible, because Bloooms exclusively works with bamboo, which is eminently suitable to apply heating. It’s a stable material, that conserves its shape and properties when heated. A sensor triggers the heating the moment someone sits down at the desk, and turns it off when no one is sitting at the desk. The heating can be individually adjusted, and is therefore excellently suited to be used in spaces where there are several people at work.”

Bloooms heated desk. The company is working on a new version of their heated desk, which can be controlled by a laptop and will be ready in a few months. Related: Several readers have sent us a link to a prototype of a thermoelectric bracelet. It monitors air and skin temperature, and sends tailored pulses of hot or cold waveforms to the wrist to help maintain thermal comfort. Heat the individual, not the building.

Related articles:

• Heat Your Clothes, Not Your House
• Insulation: First the Body, then the House
• The Solar Envelope: How to Heat and Cool Cities Without Fossil Fuels
• Sunbathing in the Living Room: Tiled Stoves
• More heating technology & heating strategies

A rocket stove is not quite as efficient and clean-burning as a masonry heater, but it is much more DIY-friendly to build. The idea is that the configuration allows excess oxygen to increase the burn temperature of the fire. Hotter temperature means you want to store the heat energy into a high thermal mass material. Lots of great links at I fucking love rocket stoves.

“The town I live in is located near the Alberta-BC border, about 100 miles north of the US Canada border. Winters here are long and cold, but many days are crystal clear and sunny.”

“Our tool shed has a south-facing wall which was ideal to mount a solar thermal direct-air collector panel. The collector panel exterior dimensions are 48” high x 49.5” wide. Total budget: $200.00 Result: 16 sq ft harvest up to 6 kWh/day.”

Build a Solar-Thermal Direct-Air Heater (PDF). Introduction (and another project) here.

“I had a lot of motivators here, but the primary motivator was the greenwashing being done around fluorescent light bulbs. My power company sent me literature telling me that I should replace all of my incandescent light bulbs with fluorescent light bulbs to save energy and money. Based on my lighting usage, the most I could possibly save is $5 per year. Yet, with changing my heating habits, I think I have proven that I can save $500 per year.”

Read more: Micro heaters cut 87% off my electric heat bill. Via Treehugger. Previously: Insulation: first the body, then the home.

Dutch inventor Kees van der Geer sends us this paper and wants to know what we think of it. Comments are open.

“Heating with a sun collector costs nothing and contaminates nothing. In this article I propose a solar heating system consisting of a large solar collector, suitable for the heating of a house and a heat store, capable to bridge a week of cloudy weather. Both are made from simple materials.”

“Maybe a practical solution to make a heat store is to buy a inflatable swimming pool of 17m3 and construct an insulating box around it. ”

Large area solar heating system (pdf), Kees van der Geer, 2011. (Artículo en Español).

Picture gallery. Previously: Sunbathing in the living room: oven stoves and heat walls.