Runwise.

Right now, a sensor in a Bronx basement is overruling a fifty-year-old thermostat.

It is a cold morning in New York, and somewhere in a six-story walk-up the boiler wants to roar to life on its old fixed schedule. A small wireless sensor, taped quietly inside an apartment, disagrees. It has been watching. The building is already warm enough. The boiler stands down. Multiply that single decision across more than 10,000 buildings and you have Runwise - a company that turned the most boring room in the building into software.

Runwise does not build skyscrapers or smart thermostats for your living room. It rebuilds the guts of real estate that everyone else ignores: the heating, cooling, water, and electrical systems that hum in the background and quietly burn money. The pitch is almost rude in its simplicity. Most buildings run on technology older than the people complaining about the heat. Runwise replaces the brains, not the bricks.

Two identical buildings. One burns 80% more fuel. Nobody could say why.

Before Runwise existed, Jeff Carleton managed roughly 150 buildings across New York City. It is the kind of job that teaches you where the bodies are buried, mechanically speaking. He noticed something that should not have been possible: two near-identical buildings on the same block could differ in energy use by 70 to 80% per square foot. Same bricks, same weather, wildly different bills.

The culprit was control, or the lack of it. A traditional heating system runs on a schedule a technician set years ago and forgot. It does not know if it is mild outside. It does not know the third floor is sweating with the windows open. It just runs, faithfully and stupidly, the way it has since the Johnson administration. Overheating is not a comfort feature. It is a leak you cannot see.

There was also a deadline arriving. Cities started writing the inefficiency into law. New York's Local Law 97 caps carbon emissions for large and mid-sized buildings, with fines for the ones that miss. Suddenly the invisible leak had a price tag, and it was due.

Wire nothing. Sense everything. Install it before lunch.

In 2010, Carleton teamed up with Lee Hoffman, a repeat founder who had been building software companies since 2004, and Mike Cook. The bet was contrarian for proptech: do not ask landlords to rip out their mechanical systems or run new wire through century-old walls. Instead, drop in proprietary wireless hardware and battery-powered sensors that listen to the building and let software make the call. The whole thing goes in within a day, with batteries rated for about a decade.

It was, in the politest possible terms, an unsexy bet. No glamorous hardware, no consumer app with a cult following - just the patient business of making old boilers behave. That turned out to be the point. The least fashionable problem in real estate was also the most expensive one.

A platform that runs your building at the minimum it can get away with.

The core idea is restraint. Indoor sensors report real conditions in real time, machine learning predicts what the building actually needs, and Runwise runs the heating, cooling, and water systems at the lowest setting that keeps tenants comfortable. The result is fuel consumption cut by 20 to 25%, typically paying for itself in under five months. Over time the platform has grown from heat into a full stack of building systems.

The numbers do the bragging so the founders don't have to.

Skeptics are right to ask whether this actually works at scale, so here is the receipt. Runwise serves real estate's heavyweights - Related, Equity Residential, FirstService Residential, Rudin, LeFrak, UDR, Douglas Elliman, AKAM - plus public giants like the MTA and the Port Authority, and utility National Grid. The platform has saved customers more than $100 million in energy costs to date, and the company grew roughly 30X from its seed round.

The investors noticed too. The 2025 Series B was led by Menlo Ventures - whose Steve Sloane joined the board - with MassMutual Ventures, Nuveen Real Estate, Munich Re Ventures, and Multiplier Capital joining returning backers Soma Capital, Alumni Ventures, Helium-3, Cooley, and Fifth Wall. A round being twice oversubscribed is the venture world's version of a standing ovation.

Decarbonization without the demolition.

Runwise's mission is almost suspiciously practical for a climate company: make the buildings we already have run far better, today, without tearing them down. Real estate is one of the largest sources of carbon emissions, and the slowest to change. By optimizing existing systems instead of waiting for everything to be rebuilt, Runwise turns climate action into a line item that landlords actually want - because it lowers the bill.

The boiler in the basement just got smarter than the building above it.

Climate laws are spreading beyond New York. Summers are setting records, and the CNBC cameras now show up when the heat does. Every city writing emissions rules creates another market for a company that can make an old building compliant in a single afternoon. The fresh $55 million is aimed exactly there: more systems, more cities, more boilers told to calm down.

So return to that cold Bronx morning. The boiler wanted to roar. The sensor said wait. The building stayed warm, the bill stayed low, and a little less carbon went up the flue - and nobody in the apartments noticed a thing. That is the whole trick. Runwise's biggest win is the one you never feel. The least glamorous room in the building turned out to be the one most worth rewiring, and it only took software to prove it.