Whspr launches 4 kW propane heat pump for space-constrained homes

Dutch startup Whspr has unveiled a 4 kW residential heat pump system designed for terraced houses.

The heat pump has been developed primarily for the Dutch terraced-house market, where space constraints, existing hydronic heating systems, and limited electrical connection capacity can complicate the replacement of gas boilers with larger heat pumps.

“When it comes to bridges, elevator cables, or structural engineering, oversizing is usually a wise move: you want a generous safety margin. However, that intuition doesn’t apply to hybrid heat pumps. After all, the central heating boiler can still heat the house effectively when needed,” the manufacturer said in a statement. “That is why we at Whspr deliberately chose a 4 kW capacity. For most homes, that is enough to cover 75–80% of their space heating needs. If you were to opt for 6 kW, the heat pump would be 50% larger, heavier, and more expensive, yet it would meet only an additional 3–4% of the heating demand. In other words, spending more on extra capacity yields almost no additional benefit.”

According to the company, a key advantage of the 4 kW capacity is that the unit can operate steadily from early autumn through late spring without frequent on-off cycling. “This is excellent for both efficiency and longevity, resulting in a faster payback period and fewer problems over the unit’s lifetime,” it added. “We didn’t choose 4 kW because we foresaw the future, but because it represents a superior solution from both technical and economic standpoints. It is gratifying to see that grid congestion, technological developments, and government policy are steering the market precisely in the direction where Whspr is ready to meet the demand.”

The monobloc unit measures 600 mm × 600 mm × 900 mm and has a maximum electrical input of 1.7 kW. It can be connected to a standard 230 V electrical supply, which the manufacturer says can simplify installation in existing homes.

According to Whspr’s product specifications, the heat pump has a seasonal coefficient of performance (SCOP) of 4.51 and an A+++ energy efficiency rating. It has a stated sound power level of 50.8 dB(A), which Whspr says was verified by testing organization Kiwa. The manufacturer claims its acoustic design reduces noise by 80% compared with conventional heat pumps.

The system is configured as an outdoor monobloc, keeping the R290 refrigerant circuit outside the building.

Whspr said it opted for a 4 kW system after field-testing the technology in 18 homes with the support of Dutch utility Eneco. According to the company, the trials indicated that the heat pump could cover roughly 75% or more of annual space-heating demand in its target housing segment without requiring a larger electrical connection.

Whspr has begun commissioning the first series-production units, with manufacturing reportedly taking place in Belgium. Commercial deliveries are expected toward the end of 2026.