Kelvin's insulated radiator wrap cut steam-heat energy 43% without replacing the boiler

Inside an 80-year-old apartment complex in Brooklyn, steam heat had always been chronically uncomfortable: top-floor apartments hit 90 degrees even with windows open on a cold January day, while lower floors never got warm enough. Over the past few years the buildings retrofitted Kelvin's Cozy — an insulated enclosure around each old radiator with a sensor and small fan — and tenants gained app control over their own temperature. Measured energy use fell 43%.

CEO Marshall Cox designed Cozy more than a decade ago to deal with his own overheated apartment, and his framing is financial: pathways to decarbonize that a business would choose even without legislation. The obstacle he targets is the replacement cycle — with boilers, people don't replace them until they die, and a dead boiler in midwinter means an emergency swap for another gas unit, because heat pumps need wall penetrations, wiring upgrades and cold-weather protection.

Kelvin's 2024 plan layers on top of the retrofit: pair Cozy with low-cost window heat pumps that only run above freezing (avoiding ice-protection hardware), backed by thermal batteries that charge at night and can earn utility payments for shaving peak demand — revenue that helps cover installation. Cozy stays as the cold-weather and backup system, and the data it collects lets Kelvin design each building's final all-electric system in advance, so when the boiler finally dies, it is not an emergency.

Don't wait for the boiler to die — wrap each radiator in a sensor-fan-insulated enclosure so steam heat becomes controllable room by room while the old plant runs

It escapes the replace-on-failure trap: with a working heater in every apartment, the boiler's eventual death stops forcing another gas purchase.

Control, not new generation, was the waste — evening out the heat fixed both the 90-degree top floors and the cold ones while burning 43% less energy.

Thermal batteries charging off-peak turn the heating system into demand-response revenue that offsets the upfront cost.

Tenants get direct control of their own temperature for the first time, which makes the retrofit politically easy in occupied buildings.

Running data from thousands of radiator-hours becomes the engineering basis for sizing the final heat-pump system.

The cheapest step is often not replacing the plant but making it controllable. Savings that pay for the retrofit, plus a first thermostat for tenants, buy the time and data electrification needs.

A $100 million financing deal announced with the March 2024 plan helps building owners pay for installations. New York City's emissions law for large buildings took effect in 2024 with strict limits due by 2030, and Washington D.C. has a similar law, giving owners a deadline; Kelvin is targeting buildings that want to cut carbon for financial reasons first, pairing Cozy retrofits with heat pumps and thermal batteries.