Since 1882, Manhattan has delivered steam into the homes and businesses of its citizens. It is used for: pressing linens at The Waldorf Astoria; cleaning crockery and heating food in restaurants; washing clothes at dry cleaners; sterilizing medical equipment at NewYork-Presbyterian Hospital; by the Metropolitan Museum of Art to control the humidity levels and temperatures around its artwork. And it is used by Manhattanites, in both iconic buildings and regular apartment blocks, to heat their space and water.

Steam functions like any other utility: produced centrally, metered, and delivered into homes and businesses through a 105-mile-long grid of pipework. Like electricity, sewage, and water, it plays an integral part in the daily operation of the city.

Today, the Manhattan steam system is responsible for heating 1.8 billion square feet of residential, 700 million square feet of commercial, and 90 million square feet of industrial floorspace. This represents over three quarters of Manhattan’s total residential footprint.

Steam enabled the growth of Manhattan, providing efficient heating to an increasingly vertical city. Many other cities have adopted district-level heating systems, but very few use steam to distribute that energy. Why does some infrastructure survive while others become obsolete? 

A short history of heating

Heating represents around half of all global end-user energy consumption. Much of this energy is spent warming homes, offices, and water – for cooking, cleaning, and washing – but roughly half goes toward various industrial uses and a smaller percentage toward agriculture. Keeping spaces warm is amongst the most foundational uses of energy there is.

Before modern central heating, keeping homes warm was inefficient, inconvenient, and sometimes deadly. Most residential buildings would be centered around a fireplace or stove, often burning wood, coal, surplus crops, or dung. Traditional fireplaces are immensely inefficient, drawing in 300 cubic feet of air per minute for combustion and expelling up to 85 of the heat generated up the chimney. They are inconvenient because the fuel source needs to be regularly replenished: felling, hauling, and splitting firewood could take up to two months of human labor per person per year. And they are deadly because these sorts of solid fuels, full of impurities, are highly polluting. A recent study found that a fireplace pumps out 58 milligrams of particles under 2.5 microns in diameter (PM2.5s) per kilogram of firewood burnt. This means that every hour you spend in a room with a fireplace burning wood reduces your lifespan by about 18 minutes, equivalent to smoking 1.5 cigarettes.

Efficiency and pollution concerns motivated the rediscovery and refinement of central heating systems, moving the production of heat away from its consumption. James Watt laid the groundwork in the late 1700s, connecting a system of pipes to a central boiler in his own home.

In 1805, William Strutt heated cold air using coal and distributed it throughout homes using ducts; around the same time, some wealthier homes in France began using similar fire-tube hot air furnaces.

By 1863, the radiator had taken definitive form, perhaps the most significant breakthrough in modern household heating. Running steam through pipes that have been folded over many times allows for a large amount of surface area in a compact space. The heat is then transferred from the steam into the ambient environment via convection and by directly radiating into the room. Individual radiators can also be fitted with valves, which allows for heating control room-by-room.

While the radiator allowed for much better distribution of heat within a building, each building needed its own boiler. But on-site boilers, especially those for larger buildings, came with both economic and ergonomic limitations. Steam heating required large boilers, coal storage areas, and extensive piping systems, which take up valuable floor space. As the systems became more advanced, they often also became more complex, necessitating skilled technicians for installation and maintenance.

Coal logistics presented its own set of problems. The regular delivery, storage, and handling of large quantities of coal is labor- and space-intensive: heating the Empire State Building would need more than 45 tons of coal per day, roughly two shipping containers’ worth. Thomas Edison’s first electric power station on Pearl Street opened in 1890 and needed upwards of 20 tons of coal each day. All this coal needed to be moved across bridges or via boat onto Manhattan Island for storage in a city where space was increasingly at a premium. The price of prime parcels of land increased tenfold between the 1790s and the 1880s, spiking from $400 an acre in 1825 to over $1 million an acre at the end of the century (over $30 million in today’s dollars).

Nor is all coal created equal. Boilers and furnaces need an expensive class of coal to burn hot enough. Anthracite coal, with its high carbon content (between 92 and 98 percent) and few impurities, burns hot and clean but is difficult to light: one exasperated user declared that ‘if the world should take fire, the Lehigh coal mine would be the safest retreat, the last place to burn’. (This would have been a bad strategy: in 1962, the anthracite seam under Centralia, PA – 25 miles to the west of Lehigh County – caught on fire and is still burning today.)

Bituminous coal is much softer, with a lower carbon content (between 45 and 86 percent); it therefore burns less energetically and pollutes much more. And all coal needs to be stored, handled, and its ashes cleared out regularly.

The unpleasantness of soot and smoke led US cities to begin to legislate against it in the 1880s, although these restrictions were often ignored. When strikes drove up the price of anthracite in 1902 and some New York City plants switched to bituminous coal, the resulting smoke choked the city, violated local ordinances, and alarmed residents. Pollution encouraged invention: from the 1830s to the 1880s, the ‘patent office . . . groaned with inventions to save fuel, abolish smoke, evaporate water and utilize steam . . . still leaving a great need unsupplied’, according to a contemporary account.

The growth of Manhattan in the nineteenth century

Between 1850 and 1900, New York’s population ballooned. Manhattan alone grew from 515,000 to 1.8 million residents. This increase led to severe overcrowding, with population densities in some areas reaching 632,000 people per square mile, ten times higher than today.

Overcrowding led to both moral and public health concerns, and anti-slum legislation was introduced to try to improve living conditions. This made space in Manhattan still more scarce. Elevated train lines, such as the Ninth Avenue Line, which opened in 1878, allowed the city’s effective size to increase and the partial suburbanization of the outer city. But fares weren’t cheap enough to allow low-wage laborers to commute regularly to and from the new communities forming uptown. If the city were to continue to grow, it would need to build upward.

Two major innovations allowed the development of ever-taller buildings. Physically climbing up stairs – bringing food, water, and fuel with you – places a practical limit on how high a building can practically be: as high as land prices rose, no Ancient Roman, medieval Byzantine, or Hausmannian residential building went above six storeys. The introduction of the safety elevator, by Elisha Otis in 1852, made taller buildings practical and desirable. Otis’s design incorporated a safety brake that would engage if the hoisting cable broke, alleviating fears of catastrophic falls.

Concurrent with safety elevators was the use of steel building frames. Traditional brick and stone structures face several limitations that prevent them from exceeding around 12 storeys, the most important of which is weight distribution: as a building gets taller, the weight of the upper floors puts enormous pressure on the floors below.

Advancements in steel production, including the Bessemer process – oxidizing impurities in molten iron by blowing air through it – made it both affordable and economical to use steel frames, which allowed for a ten times higher strength-to-weight ratio. Designing the building around a skeleton of vertical steel columns and horizontal I-beams allowed buildings to redistribute their weight into this structure, freeing up tensile pressure from the walls and floors. This meant that the rest of the building could be made from lighter non-load-bearing materials, making it possible to build higher still.

So New York shot up. In 1890, the tallest building reached 18 storeys. By 1899, the Park Row Building stretched to 31 stories, and in 1908, the Singer Building soared even higher to 41 stories. Vertical expansion allowed the city to create more residential and commercial space, but that space needed to be heated, powered, and watered.