At first glance, it looks like a bulky window air conditioner. In reality, it is a new generation window-mounted heat pump, designed to cope with severe winter temperatures while cutting energy use in buildings that were never planned for modern heating systems.
A heat pump that fits directly into the window frame
Along the US East Coast, winter usually means relying on ageing radiators or energy-hungry space heaters. This winter, a compact solution is quietly changing that habit. Developed by Chinese manufacturer Midea, this window heat pump is tailored for the traditional sash windows found in millions of older American apartments.
Instead of drilling through thick masonry or installing outdoor units, residents simply slide the device into an existing window opening. Early trials in New York suggest that a capable DIY installer can complete the setup in less than an hour, without specialist tools or professional help.
The goal is clear: bring heat-pump efficiency to older, hard-to-upgrade city buildings, one window at a time.
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By focusing on ageing rental stock and shared housing, where landlords often resist major renovations, Midea is addressing a largely untapped urban heating market. The promise is straightforward: a reversible unit that provides winter heating and summer cooling, installed almost as easily as a portable air conditioner.
How it delivers heat down to –22°C
Inside, the system relies on a familiar principle: an air-to-air heat pump. The difference lies in its design and, more importantly, the compressor. While many compact heat pumps lose effectiveness in deep cold, this model is engineered to keep producing useful heat well below freezing.
Data from pilot programs indicates stable operation down to –22°C, with a theoretical lower limit close to –25°C. Under those harsh conditions, heating output drops to around 1.4 kW, sufficient for a well-insulated room or small living space. In milder weather, around 8°C outdoors, output rises to roughly 2.6 kW, similar to a standard wall-mounted residential heat pump.
The compressor continuously adjusts its speed to match outdoor conditions, prioritising precision over brute force.
Traditional systems relied on simple on/off cycles, blasting at full power until the target temperature was reached, then shutting down entirely. Midea’s variable-speed compressor instead ramps output up or down smoothly. This reduces wasted energy and limits sharp power spikes that inflate bills and strain electrical networks.
Why modulation reduces energy bills
In a variable-speed heat pump, the compressor rarely operates at maximum output. Most of the time, it runs at a steady, moderate level that closely matches the room’s actual heat demand. This approach delivers several advantages:
- Lower electricity consumption, especially during mild winter periods
- More stable indoor temperatures with fewer hot-and-cold swings
- Reduced mechanical wear, which can extend system lifespan
- Quieter operation at lower speeds
For tenants, the takeaway is simple: more comfort per kilowatt-hour, particularly in regions where temperatures stay below zero for weeks at a time.
Low noise levels, heavy construction
Noise has long been a drawback of compact window-mounted heating and cooling units. Here, the manufacturer claims meaningful progress. A dedicated low-noise mode is rated at around 29 dB(A), comparable to a quiet library. Under normal operation, sound levels rise to about 51 dB(A), similar to everyday conversation.
The trade-off appears in size and weight. At approximately 59 kg, this is not a lightweight appliance. It occupies a significant portion of the window opening, partially reducing natural light and limiting how fully the window can be opened.
Quiet performance and efficiency come at the cost of a bulky, semi-permanent window installation.
This compromise will not suit everyone. Residents who prioritise clear views or rely on every centimetre of window space, particularly in small studios, may prefer slimmer wall-mounted systems. There is also a psychological barrier: some landlords and tenants may be uneasy about a heavy unit resting in a window frame, despite mounting hardware and safety features.
Pricing and early adopters
Cost remains a significant hurdle. Early North American pricing places the unit between $2,800 and $3,000, before incentives or rebates. While Midea suggests prices will drop as production increases, the device currently sits above many portable heaters and even some split heat-pump systems.
At this price point, early buyers are more likely to be institutional customers rather than individual tenants. Housing authorities, social landlords and large property managers see value in retrofitting entire buildings without invasive construction. Pilot programs are already underway in cities such as Boston, and in colder parts of Canada where low-temperature performance is especially attractive.
Why France is excluded, and the UK is not
Despite strong interest in New York, households in France are unlikely to adopt this system anytime soon. The obstacle is not regulation or efficiency, but window design. The unit is built specifically for vertical sliding sash windows, common in North America and parts of the UK, but rare in France, where side-hinged and tilt-and-turn windows dominate.
Without a compatible window type, the current model has no secure mounting option. Adapting it to European window styles would require an entirely new frame and fixing system, effectively creating a different product.
The success of this heat pump depends as much on window geometry as on advanced compressor technology.
Countries such as Canada and the United Kingdom, where sash windows remain widespread in older housing, are better positioned for similar solutions. In the UK, landlords dealing with draughty Victorian terraces and strict planning rules could see appeal in a non-invasive, reversible heating option that avoids exterior alterations.
What lower energy use really means
Claims of reduced energy consumption depend heavily on what system the heat pump replaces. Compared with electric resistance heaters, such as fan heaters or oil-filled radiators, an efficient air-to-air heat pump can typically deliver two to four units of heat per unit of electricity. This ratio is known as the coefficient of performance, or COP.
For example, a tenant spending £100 per month on electric radiators could, in theory, see costs fall to around £35–£40 with a heat pump operating at a COP of 3, assuming similar usage and tariffs. In reality, insulation quality, air leakage and thermostat habits all influence final savings.
When compared with gas boilers, the calculation becomes more complex. While gas is often cheaper per kilowatt-hour, heat pumps use far less input energy. In areas with a low-carbon electricity mix, switching from gas to a high-efficiency heat pump can reduce both running costs and emissions, particularly in well-insulated flats.
Key questions for tenants and landlords
Anyone considering a window heat pump should address several practical points before committing:
- Can the window frame safely support a device weighing over 50 kg?
- Does installation affect fire escape routes or building regulations?
- How much daylight and ventilation will be lost?
- Is there a suitable electrical outlet with sufficient capacity?
- Who pays for electricity, and who owns the unit in rental properties?
Clarifying these issues early can prevent disputes, especially in protected buildings or complexes with shared electrical infrastructure.
Heat-pump efficiency on the coldest nights
Heat-pump specifications are filled with acronyms, but one of the most important in winter is SCOP, or seasonal coefficient of performance. While COP measures efficiency at a single temperature, SCOP reflects performance across an entire heating season.
For a unit claiming operation down to –22°C, low-temperature efficiency is critical. A system that performs well at 10°C but struggles at –15°C may disappoint in cities like Montreal or Boston. This is why manufacturers are investing in advanced refrigerants and compressor designs that maintain output in extreme cold.
In practice, a New York tenant in an unrenovated pre-war building could combine basic draught-proofing, a window heat pump and smart controls. By lowering night-time temperatures and letting the variable-speed compressor handle gradual warm-up, they can avoid noisy backup heaters. The result is improved comfort, lower bills and reduced emissions, all without drilling into brick walls.
Scaled across thousands of apartments, these incremental upgrades can significantly cut demand on urban gas networks and ease pressure on ageing power grids during cold spells. This window-mounted heat pump is only one example, but it illustrates how targeted technology, adapted to existing buildings, can reshape how cities stay warm when temperatures plunge to –22°C.
