From Brooklyn walk‑ups to ageing Manhattan towers, a new kind of electric heater is starting to appear under sash windows, promising strong heat in brutal cold and lower energy bills in buildings that were never designed for modern climate tech.
A window heat pump shaking up New York’s old radiators
For generations, New Yorkers have survived winter with two options: crank up clanking steam radiators, or plug in energy‑hungry space heaters and hope the wiring holds. This season, a third option is gathering attention: a window‑mounted heat pump built specifically for the classic US sash window.
The device, developed by Chinese manufacturer Midea, slides into a vertical window much like a traditional room air conditioner. Instead of just cooling in summer, it can both heat and cool, effectively acting as a small reversible air‑to‑air heat pump for a single room.
The main selling point is simplicity. Early users report that installing the unit takes under an hour. No holes in thick brick walls. No scaffolding. No waiting for a certified installer. For tenants in old buildings, that ease of setup changes the equation.
This new heater targets the hardest buildings to decarbonise: old, dense urban housing where drilling through walls is a logistical and legal nightmare.
In contrast, a conventional wall‑mounted split heat pump typically needs a full day of professional work, core drilling, outdoor brackets and lengthy piping. For many leaseholders and renters, that is either too expensive or simply not allowed.
A compact system that keeps working down to –22°C
The headline claim is bold: the window unit keeps delivering heat even when outdoor temperatures plunge to –22°C, with a theoretical operating floor at –25°C. That figure matters for cities like New York, Boston or Montreal, where Arctic blasts are becoming more frequent.
Technically, this is still a standard air‑source heat pump. It takes heat from outside air and moves it indoors using refrigerant and a compressor. The difference lies in how that compressor behaves.
Midea has equipped the unit with a new generation inverter compressor that constantly adjusts its power rather than cycling on and off.
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Continuous modulation allows the compressor to match output to conditions, trimming energy use while keeping the room temperature more stable.
At extreme cold, the unit’s heating capacity drops to about 1.4 kW, which is enough to warm a typical bedroom or small living room. Once outdoor temperatures rise to around 8°C, output climbs to 2.6 kW, roughly comparable to many wall‑mounted residential units.
Why that matters for energy bills
Traditional electric heaters simply convert electricity into heat, one kilowatt in for one kilowatt out. Heat pumps are different: they move heat instead of generating it, so each kilowatt of electricity can deliver two, three or even more kilowatts of heat, depending on conditions.
That ratio, known as the coefficient of performance (COP), falls in very cold weather. The ability to keep running at –22°C without switching to a costly resistance backup can shave a meaningful chunk off winter bills, especially in regions with high power prices.
- Electric space heater: ~1 unit of heat per unit of electricity
- Typical heat pump at mild temperatures: 3–4 units of heat per unit of electricity
- Cold‑climate heat pump at –15 to –20°C: often 1.5–2.5 units of heat per unit of electricity
The New York window unit slots into that cold‑climate category, chasing households currently reliant on inefficient plug‑in heaters to top up old central systems.
Quiet operation, heavy footprint
One of the main complaints about older radiators and window air conditioners is noise. Steam pipes bang and hiss; ageing AC compressors rattle through the night. The new window heat pump tries to counter that with a low‑noise mode rated at 29 dB(A) — about the level of a whisper in a library.
In standard operation, noise rises to around 51 dB(A), still moderate for a mechanical system sitting in a window opening. For small flats where bedroom and living room are the same space, that can make the difference between using the machine every day and leaving it off on winter nights.
There is a trade‑off, though. The unit weighs roughly 59 kg and occupies a sizeable chunk of the window opening. Light is partially blocked. The lower sash becomes largely unusable. For some residents, especially those in compact studios, giving up that much glass is a step too far.
The device is quiet and efficient, but it turns a classic sash window into something closer to a permanent mechanical wall.
Who this heater is really for
Then there is the price. Early models in the US market are coming in between $2,800 and $3,000 before any subsidies. That pushes the product firmly towards professional buyers, social landlords and pilot programmes rather than individual tenants on tight budgets.
Midea says costs should fall as production scales, but for now the company is focused on deals with housing providers in cities such as Boston and on cold‑climate tests in Canada. The technology is being positioned less as a gadget and more as a tool for upgrading entire building portfolios without the chaos of deep renovation.
Why most Europeans can’t use it yet
Despite growing interest around heat pumps in Europe, this particular device remains largely confined to North America and a handful of countries with similar window designs. The reason is surprisingly simple: geometry.
The unit is engineered specifically for sash, or “guillotine”, windows that slide up and down. Those are standard in the United States, Canada and parts of the UK, but rare in France, Germany and much of southern Europe, where outward‑opening casement windows dominate.
Trying to mount the current design into a typical French window would create structural and safety issues. Frames are not shaped to grip the unit, and many open in a way that would leave the heavy box hanging at awkward angles.
Until manufacturers design variants for European‑style casement windows, the window heat pump will remain a niche solution tied to legacy sash frames.
For now, France is effectively out of the game. The UK could become an interesting test bed, as many Victorian and Edwardian properties still sport timber sash windows, especially in London and other large cities frequented by private landlords.
What this means for urban heating
The rise of a plug‑in‑style heat pump highlights a broader shift in how cities might tackle emissions from old housing. Deep retrofits with external insulation and fully integrated heat pump systems remain the gold standard, but they are slow, disruptive and costly on a street‑by‑street scale.
A modular window unit does not fix leaky walls or single glazing. It does, though, offer a fast, reversible upgrade for individual flats inside buildings where owners struggle to agree on major works. In rental markets with huge numbers of short‑term tenants, that flexibility holds appeal.
| Aspect | Traditional radiator + space heater | Window heat pump |
|---|---|---|
| Installation | Existing, plus plug‑in devices | ~1 hour, no drilling |
| Cold‑weather performance | Good, but often wasteful | Maintains output to –22°C |
| Energy efficiency | Low with electric heaters | Higher, heat pump operation |
| Visual impact | Little change | Partially blocked window |
| Target user | Any household | Landlords, pilot projects |
Key concepts behind the technology
For anyone new to heat pumps, a few terms help make sense of the hype. A “cold‑climate air‑source heat pump” is simply a machine that has been tweaked to work efficiently at lower outdoor temperatures, typically with better compressors, smarter controls and optimised refrigerants.
The unit’s ability to vary output continuously is known as inverter technology. Instead of switching the compressor fully on and off like a light, the system can slow it down or speed it up. That cuts the sharp temperature swings that many people associate with older electric heating and can lengthen the life of the hardware.
Noise figures such as 29 dB(A) and 51 dB(A) use a logarithmic scale. That means a 10‑decibel jump sounds roughly twice as loud to the human ear. A small change on paper can feel quite noticeable in a quiet bedroom at night.
How this could play out in a typical flat
Imagine a one‑bedroom rental in Brooklyn with a single ageing steam radiator under the window. On most days, building‑wide heating is either too hot or barely there. The tenant brings in two plug‑in heaters, which push up the electricity bill and sometimes trip the breaker.
Swapping the radiator‑plus‑heaters combo for a window heat pump changes the dynamic. The landlord pays for installation in under an hour. The tenant sets a precise room temperature with a remote or smartphone app. During a –18°C night, the unit runs constantly but still uses less power than the two old plug‑ins working at full blast.
Over a winter, that shift could stabilise indoor comfort, reduce the strain on old electrical circuits and cut carbon emissions if the local grid has a decent share of low‑carbon power. It does not solve every problem in the building, but it moves the needle with relatively little disruption.
There are risks to watch. Blocking a window can affect fire‑escape routes in cramped apartments. Poorly secured units might be vulnerable in high winds. Building codes and landlord‑tenant rules will determine how fast such technology spreads, especially in crowded historic districts.
For city authorities under pressure to decarbonise heating without tearing apart millions of flats, a heater that works at –22°C, sips electricity compared with old space heaters and hangs from an existing window frame is likely to stay on the policy radar for years to come.
Originally posted 2026-03-10 13:54:55.