If you live in a century-old apartment building, you know the struggle: sweltering in winter when radiators blast, shivering in summer with no AC. Now, smart heat pumps with breakthrough window-unit designs are solving this decades-old problem—without tearing down walls or rewiring entire structures. These systems deliver precise heating and cooling while slashing energy use by up to 25% through intelligent building-wide management.
Credit: Gradient
New York City alone houses over one million pre-war apartments stuck with inefficient steam radiators or clunky window AC units. Nationwide, nearly 40% of residential buildings were constructed before 1980, predating modern HVAC standards. Retrofitting them has long been cost-prohibitive—until now. Gradient's horseshoe-shaped heat pumps, paired with new Nexus software, enable landlords and housing authorities to upgrade comfort and efficiency without structural overhauls.
Why Old Buildings Resist Modern HVAC Upgrades
Retrofitting century-old structures presents unique headaches. Many lack ductwork, have single electrical meters serving entire floors, and feature narrow window frames incompatible with standard units. Traditional solutions demand invasive construction: cutting walls for ducts, upgrading electrical panels, or installing expensive geothermal loops. Costs often exceed $15,000 per unit—impossible for public housing or rent-stabilized buildings.
Steam radiator systems compound the problem. They operate on an all-or-nothing principle: boilers fire up for the entire building regardless of individual needs. One resident cranking heat to 80°F forces everyone else to suffer—or open windows in January, wasting energy. These systems also can't provide cooling, leaving residents vulnerable during increasingly intense heat waves.
The Horseshoe Design That Changes Everything
Gradient's innovation starts with form. Its heat pump wraps around the window frame in a sleek U-shape, preserving views and natural light while maintaining a tight thermal seal. Unlike bulky window AC units that block half the glass, this design fits historic double-hung windows common in pre-war buildings. Installation takes under two hours per unit—no masonry work, no permits beyond basic landlord approval.
The unit itself moves refrigerant between indoor and outdoor coils to heat or cool air efficiently. During winter, it extracts ambient heat from frigid outdoor air (even below 0°F) and amplifies it indoors—a process three times more efficient than electric resistance heating. In summer, it reverses the cycle, dehumidifying while cooling. Crucially, it runs on standard 120V outlets, avoiding costly electrical upgrades.
Nexus Software: The Brain Behind Building-Wide Efficiency
Hardware alone wouldn't solve the behavioral challenge: when tenants share one meter, nobody feels accountable for energy use. Gradient's new Nexus platform introduces intelligent guardrails without sacrificing personal comfort.
Building managers set temperature boundaries—say, 62°F minimum in winter and 78°F maximum. Residents control their unit within that range via a simple app or physical interface. If someone tries overriding limits, the system gently resists rather than shutting down entirely, avoiding tenant frustration. Real-time dashboards show aggregate energy use per floor or building, helping managers spot anomalies.
In a recent Brooklyn public housing pilot, managers capped heating at 78°F after noticing consistent overnight spikes. The next day, building-wide consumption dropped 26% without resident complaints. One superintendent noted, "People didn't even realize they'd been overheating their apartments until they experienced consistent comfort at lower settings."
Real-World Impact in Public Housing and Campuses
Gradient has moved beyond pilots into scaled deployments. The New York City Housing Authority installed 300 units across three developments last fall, targeting buildings where boiler replacements were imminent. Residents reported fewer temperature swings and the unexpected gift of air conditioning during a record-breaking October heat wave.
College campuses present another ripe opportunity. Many dorms built in the 1960s–70s lack cooling entirely. With students now attending classes through September—and heat waves disrupting sleep and study—administrators face pressure to adapt. A Midwestern university recently retrofitted two freshman dorms using Gradient's system ahead of the 2025–26 academic year. Maintenance staff appreciated remote diagnostics: when a unit in Room 314 showed reduced airflow, technicians received an alert before the student even noticed discomfort.
The Hidden Win: Future-Proofing Against Climate Extremes
As climate change intensifies, aging buildings face compounding risks. Steam systems can't mitigate heat-related health emergencies. Window AC units strain aging electrical grids during peak demand and often get removed seasonally—leaving buildings vulnerable when unseasonable heat strikes.
Smart heat pumps address both heating and cooling needs while reducing grid stress. Their inverter-driven compressors ramp output gradually rather than cycling on/off at full blast. During demand-response events, utilities can signal Nexus to slightly adjust setpoints across hundreds of units—shedding megawatts of load without disrupting comfort. This capability earned Gradient inclusion in New York's Clean Heat Program, which offers rebates covering up to 50% of retrofit costs for qualifying buildings.
Cost Analysis: Why This Beats Boiler Replacement
Replacing a century-old boiler in a 50-unit walk-up typically costs $250,000–$400,000. It solves heating—but not cooling—and still leaves residents at the mercy of a single thermostat. Gradient's approach costs approximately $3,500 per unit installed, totaling $175,000 for the same building. Crucially, it delivers individualized comfort plus AC—a value-add that helps retain tenants in competitive rental markets.
Energy savings accelerate payback. Buildings using Nexus typically see 20–30% reductions in heating fuel or electricity. At current NYC utility rates, that translates to $800–$1,200 saved annually per unit. With incentives factored in, many property managers achieve full ROI within six to eight years—far faster than traditional HVAC overhauls.
Installation Simplicity Wins Over Skeptical Superintendents
Early adopters worried about disruption. Would drilling compromise historic window frames? Would residents resist new technology? Reality proved smoother than expected. Installers use non-invasive brackets that attach to existing sills. The entire process generates minimal noise or dust—critical in occupied buildings.
Tenant onboarding takes minutes. A QR code on each unit links to a video tutorial showing how to adjust temperatures or report issues. For elderly residents uncomfortable with apps, a physical dial offers manual control within manager-set boundaries. One Bronx housing director shared that after initial hesitation, her building's senior tenants now proudly demonstrate their units to visitors—especially when neighbors complain about radiator headaches.
The Road Ahead: Scaling Retrofits City by City
Gradient isn't alone in this space, but its focus on multifamily retrofits fills a critical gap. Single-family home heat pump adoption has surged, yet dense urban housing remained underserved. With Nexus now live, the company aims to equip 10,000 units across New York, Boston, and Philadelphia by end of 2026.
Policy tailwinds are accelerating adoption. Cities like Seattle and Minneapolis now require cooling access in all rental units following heat-related fatalities. Rather than mandate expensive central systems, officials increasingly endorse targeted retrofits like Gradient's as pragmatic solutions. Building codes are evolving too—New York's upcoming Local Law 97 compliance deadlines push owners toward efficient electrification.
Comfort Meets Conscience in the Retrofit Revolution
The true breakthrough here isn't just technical—it's human-centered. For decades, retrofit discussions centered on carbon metrics and utility savings. Gradient's approach starts with lived experience: the frustration of peeling off layers in January, the anxiety of sleeping through a heat wave without AC, the helplessness of having no control over your own comfort.
By preserving views, respecting historic architecture, and giving residents agency within sensible boundaries, these systems prove sustainability doesn't require sacrifice. They transform neglected buildings into resilient, comfortable homes ready for the next century—without erasing the character that makes them worth preserving.
As one Queens resident put it after her unit's installation: "I finally understand what 'just right' feels like. And my electric bill is lower. Why didn't we do this years ago?" That sentiment, multiplied across thousands of apartments, signals a quiet revolution taking hold—one window at a time.
