Kitchens blaze behind restaurant counters. Offices remain lit late into the night. Neon signs burn overhead. At street level, in the commercial districts, the familiar portrayal holds true: Tokyo is electric—a field of light, colour, and motion.

Turn the corner, and the side streets branch. Bodies brush, grills crackle, and lanterns sway. One turn farther, and the spaces between buildings narrow into alleyways of happenstance. As the ambient hum of evening revelry drops into the background, a low whir rises and falls, its shifting frequencies softening into an almost calming drone. A sudden, dense warmth meets the skin, as if the city had exhaled. 

From its illuminated skyline to its microscopic drinking dens, every layer of Tokyo generates and absorbs heat. Thermodynamically, the city is less a romance than an accumulation, and all that energy must go somewhere. Between and behind the buildings, that somewhere comes into view: small, boxy units bolted to walls, wedged into gaps, or set along the pavement.

Each box, known as shitsugaiki (室外機), meaning “outdoor unit”, forms the exterior half of a split system, part of a distributed cooling infrastructure that makes density livable. In 1982, Daikin introduced Japan’s first commercial multi-split air-conditioning system for buildings, allowing individual rooms to be cooled as needed. This made it possible for buildings to offload their thermal burden into networks of these small machines. They are everywhere, and through them, the city sheds its heat.

In cooling mode, the setting Tokyo defaults to all summer, a split-system air-conditioner draws warmth from a room and transfers it into the outdoor air. Heat is absorbed by a refrigerant, a circulating fluid that changes state to carry thermal energy, before being sent to the outdoor unit and unceremoniously released through condenser coils into the street as skin-prickling exhaust. The cool interior that city dwellers depend on in the warmer months is cleared rather than created.

Shitsugaiki become the city’s heat-rejection hardware: the point at which kitchens, lights, bodies, and appliances finally hand off what they cannot keep. This heat is absorbed by asphalt and concrete, retained within the urban fabric, and radiated back into the air. As a result, ambient temperatures rise, forcing cooling systems to work harder and pump still more heat into the already warmed streets. The process fuels the urban heat-island effect, in which the city remains significantly hotter than the surrounding countryside, particularly after dark. In this way, shitsugaiki are the public face of a relentless cycle.

In dense areas where buildings rise high, little sky is visible from the street. This reduced sky-view factor limits how effectively heat dissipates after sunset. With minimal air circulation between structures, heat lingers at ground level. Under these conditions, shitsugaiki begin to draw in their own exhaust. Engineers respond by lifting the units and spacing them to keep the ground plane clear and the air in motion. The outcome is a makeshift order, toeing the line between visual chaos and strict mechanical necessity. Confronted by a canyon of shitsugaiki in a narrow alley, I find not a mess, but an intricate response to an impossible spatial problem.

Cities like Hong Kong and Singapore converge on a similar solution. Their dense, humid environments favour distributed cooling, and the approach refined in Japan proved well-suited to these conditions, spreading widely across the region. In Hong Kong, entire facades are covered with protruding units, stacked and clustered in irregular grids; in Singapore, they repeat systematically along designated ledges, forming ordered fields of identical machines.

Back in Tokyo, the same logic explains a different spatial surprise. In low-rise residential neighbourhoods, where plots are tightly constrained, houses are often built close to the lot line, with minimal setbacks. The narrow side passages that might otherwise serve as a “back” are typically too tight—and often too poorly ventilated—to function effectively. The street-facing edge, then, becomes a practical route between room and condenser. Here, shitsugaiki migrate to the front of the home in smaller, more domestic forms.

Home comfort depends on these small boxes exporting heat into the neighbourhood, and so they often become part of modest garden arrangements. On a stroll, you will spot them topped with miniature statues, bicycles parked neatly beside them, surrounded by potted plants. There is a glimmer of urban artistry in the way residents work around their outdoor units, rendering them less an eyesore than evidence of a living system.

It is an approach that commercial and large residential developments struggle to scale, yet it points toward a solution. Japanese policy treats the urban heat island effect as a systemic issue, prescribing remedies that include green roofs and planted facades—architectural measures that absorb or diffuse heat before it can accumulate. A different version of the commercial city comes to mind: one that still glows, cooks, and works late, but is layered with vegetation, releasing less heat into its own streets.

The inquiry cannot end with admiration for the mechanics; nor can it conclude with an aesthetic appreciation of the outdoor unit alone. But for now, it remains one of the most truthful objects in the city. Stand in a narrow lane on a warm night, and you can hear it: the low mechanical whir of a place forever trying to move its warmth somewhere else.

Until we meet under burning neon,

AJ

We’re off to Japan next week. Live dispatches will follow as we travel.

The trip also serves to lay the groundwork for Tokyotheque Neighbourhoods: Volume 2. We’ve appreciated the responses to the first volume, and the glimpses of it in use through social media. As we begin the next, we’d like to ask for your help in improving it.

We’re working towards our dream city guide format. Volume 1 is a step in that direction, and in the spirit of kaizen, we’ve set up a short survey to gather feedback. If you share our enthusiasm for Tokyo, and in cities more broadly, we’d like to hear from you.

If you’ve yet to pick up a copy, the second printing of Volume 1 remains available.

Orders placed this weekend will ship before we go to Japan. Orders placed April 13–30 will ship on our return.

For those awaiting delivery, copies should be arriving shortly. Thank you for your patience.