6 kw Heat Pump
Custom Colors
The 6 kW heat pump is the step-up model in the Legom Monoblock DC Inverter range, suited to medium homes with moderate heat demand and to households where hot water production matters as much as space heating. It is an air source, air-to-water unit running on R32 refrigerant with a full DC inverter twin rotary Panasonic compressor, delivering heating, cooling, and domestic hot water from a single outdoor unit and operating down to -35°C ambient.
6 kW Heat Pump Specifications
Full published parameters for the 6 kW model, Legom Monoblock Series DC Inverter Heat Pump.
| Parameter | 6 kW — QB KFXFC-006SRI |
|---|---|
| Heating capacity range | 3.0 to 8.0 kW |
| Domestic hot water heating | |
| Heating capacity | 8 kW |
| Water yield | 172 L/h |
| Input power | 1.86 kW |
| COP | 4.3 |
| Operating current | 8.3 A |
| Heating A7/W35 | |
| Heating capacity | 6 kW |
| Input power | 1.36 kW |
| COP | 4.42 |
| Operating current | 6.1 A |
| Heating A7/W45 | |
| Heating capacity | 6 kW |
| Input power | 1.75 kW |
| COP | 3.43 |
| Operating current | 7.8 A |
| Cooling A35/W7 | |
| Cooling capacity | 5 kW |
| Input power | 1.75 kW |
| EER | 2.85 |
| Operating current | 7.9 A |
| ERP energy label | |
| ERP at 35°C | A+++ |
| ERP at 55°C | A++ |
| Compressor | |
| Type | DC inverter twin rotary |
| Brand | Panasonic |
| Capacity modulation | Stepless, 20% to 120% |
| Other components | |
| Expansion valve | Electronic expansion valve |
| Air side heat exchanger | Hydrophilic aluminium fin heat exchanger |
| Water side heat exchanger | Plate heat exchanger |
| Fan system | |
| Fan type | Low noise axial fan |
| Motor type | Brushless DC motor |
| Motor brand | NIDEC / SiGe |
| Fan quantity | 1 |
| Water side | |
| Water port size | G3/4 DN20 |
| Water yield | 1.38 m³/h |
| Water pressure loss | 25 kPa |
| Expansion tank | Not included |
| Noise, dimensions and weight | |
| Noise level | ≤54 dB(A) |
| Unit dimensions (W×D×H) | 1075 × 480 × 805 mm |
| Packing dimensions | 1165 × 530 × 925 mm |
| Net weight | 70 kg |
| General | |
| Refrigerant | R32 (GWP 675) |
| Minimum ambient operating temperature | Down to -35°C |
| Cabinet colours | 11 finishes available |
| Certification | CE, RoHS |
| OEM / ODM | Available |
Reading the COP figures. At 7°C outdoor air producing 35°C water the unit achieves a COP of 4.42, delivering 6 kW of heat from 1.36 kW of electrical input. Producing 45°C water from the same outdoor conditions, COP falls to 3.43. Both figures describe the same machine. This is why the emitter matters as much as the heat pump: an underfloor system running at 35°C extracts roughly 29% more heat per unit of electricity than radiators demanding 45°C.
Should You Choose the 5 kW or the 6 kW?
This is the most common question at this point in the range, and the answer is not simply that bigger is safer. The two models differ in three ways that matter, and each can point either direction.
Hot water capacity is the clearest difference
The 6 kW unit produces 8 kW of domestic hot water heating at 172 litres per hour, against 6 kW and 129 litres per hour on the 5 kW model. That is a 33% increase in hot water production. For a household with several bathrooms, or one where showers overlap in the morning, this difference is felt daily in a way that a small difference in space heating capacity is not.
Minimum output is the argument against oversizing
Here is the point that most buyers miss. The 6 kW unit modulates between 3.0 and 8.0 kW, while the 5 kW unit modulates between 2.0 and 6.0 kW. The upper figure gets the attention, but the lower figure is often more consequential.
On a mild spring day a well-insulated small home may only need 2 kW of heat. The 5 kW unit can throttle down to exactly that and run steadily. The 6 kW unit cannot go below 3 kW, so it must produce more heat than the building needs, reach the set point, shut off, and restart. That cycling reduces efficiency and increases compressor wear precisely during the mild months that make up most of the heating season.
This is why oversizing is a real error rather than a safe margin. A heat pump chosen one size too large spends most of the year unable to modulate low enough, cycling instead of running steadily. The 6 kW model is the right choice when the calculated heat load genuinely sits in its range, not as insurance against an uncertain calculation.
Efficiency, size and noise
The 5 kW unit is marginally more efficient at A7/W35, at COP 4.5 against 4.42, and quieter at ≤52 dB(A) against ≤54 dB(A). It is also smaller and lighter, at 60 kg against 70 kg, which can matter for installation access and mounting. None of these differences is decisive on its own, but together they mean there is no advantage in choosing the larger unit unless the load or the hot water demand calls for it.
| Consideration | 5 kW | 6 kW |
|---|---|---|
| Heating output range | 2.0–6.0 kW | 3.0–8.0 kW |
| Minimum modulated output | 2.0 kW | 3.0 kW |
| Hot water capacity | 6 kW, 129 L/h | 8 kW, 172 L/h |
| COP at A7/W35 | 4.5 | 4.42 |
| Cooling capacity | 4 kW | 5 kW |
| Noise | ≤52 dB(A) | ≤54 dB(A) |
| Net weight | 60 kg | 70 kg |
| Choose it when | Small home, low mild-weather load | Medium home, higher hot water demand |
When the 6 kW is the right choice
- The calculated heat load sits between roughly 4 and 7 kW
- Domestic hot water demand is significant, with more than one bathroom in regular use
- The property is a medium home rather than a compact two-bedroom
- Cooling demand is moderate and 5 kW of cooling capacity is useful in summer
- The system feeds emitters requiring slightly higher flow temperatures, where extra headroom helps
If your calculated load is closer to 3 or 4 kW, the 5 kW model will modulate better through the mild months. If it exceeds 7 kW, look at the 9 kW model instead.
Inside the Unit
A heat pump does not generate heat, it moves it. Refrigerant evaporates at low temperature while absorbing heat from outdoor air, the compressor raises its pressure and temperature, and that heat transfers into the water circuit through the plate heat exchanger before the electronic expansion valve drops the pressure and the cycle repeats. Because the unit transports existing energy rather than creating it, it delivers several units of heat per unit of electricity, which is what produces a COP above 1.
Key Technologies
High Efficiency Full DC Inverter Compressor
Integrating cutting-edge technology, our HVAC systems feature a high-performing DC inverter compressor and DC brushless fan motor. This innovative configuration enables seamless 20% to 120% stepless capacity adjustment. By intelligently adapting to the real-time load requirements, the compressor and fan automatically modulate their speeds during operation. This dynamic adjustment minimises energy consumption, allowing the unit to operate at an optimised level, precisely meeting the desired output while significantly reducing energy costs.
The 6 kW model uses a Panasonic twin rotary compressor paired with a NIDEC or SiGe brushless DC fan motor. In practice, modulation across the 3.0 to 8.0 kW range means the unit spends most of the heating season running steadily at partial output rather than cycling, which both improves seasonal efficiency and reduces mechanical wear on the compressor.
Verified Efficiency: ERP A+++ and COP 4.42
The 6 kW unit carries an ERP rating of A+++ at 35°C and A++ at 55°C, the European energy label classification for space heaters. At A7/W35 test conditions it achieves a COP of 4.42, delivering 6 kW of heat output from 1.36 kW of electrical input. For domestic hot water the COP is 4.3.
Three factors determine what efficiency you achieve in service. The flow temperature required has the largest influence, demonstrated by this unit's own figures: 4.42 at 35°C water against 3.43 at 45°C. Outdoor temperature is the second, since colder air holds less extractable heat. Building insulation is the third, because a leaky building forces higher flow temperatures and pushes the unit into its less efficient range.
R32 Refrigerant: Energy Saving and Environmental Protection
R32 contributes greatly to environmental protection, with a low Global Warming Potential of 675, just 32% of R410A's 2088. In the same heat pump system, its lower liquid density means the charge amount of R32 is less than that of R410A, which brings higher economic efficiency.
The heat needed to evaporate R32 is greater than that of R410A, so the required mass flow rate per unit is smaller and the COP is higher. We not only take care of your family but also contribute to protecting the earth.
There is a commercial dimension worth noting for distributors. Under the European F-Gas Regulation and equivalent rules elsewhere, high-GWP refrigerants face progressive restriction, which makes equipment charged with them harder and more expensive to service over time. Sourcing R32 today avoids selling customers into a future servicing problem.
Stable Running at -35°C
The 6 kW unit is engineered to keep operating in ambient temperatures as low as -35°C, well beyond the range in which many standard air source units lose usable output. This is what allows the model to serve as a primary heat source in cold-climate markets rather than a supplementary one.
Two elements make this possible. The full DC inverter compressor can raise its speed to compensate as the heat available in outdoor air falls, sustaining output where a fixed-speed unit simply cannot. The intelligent defrost system then clears frost from the air-side heat exchanger without the frequent, disruptive cycles that undermine cold-weather comfort in simpler designs.
Output does decline as ambient temperature drops, which is unavoidable physics for any air source heat pump rather than a limitation of this model. Cold-climate projects should therefore be sized against the local design temperature rather than the nominal rating.
Automatic Intelligent Defrosting
In cold, humid conditions frost forms on the outdoor coil and must be cleared, but how a heat pump manages that process has a large effect on comfort. Demand-based defrosting initiates a cycle only when frost is actually detected, rather than running on a fixed timer.
The result is concentrated, efficient defrosting completed in around three minutes, followed by extended heating periods of up to 90 minutes. An ordinary defrost curve, by contrast, shows frequent and incompletely effective cycles with short heating periods between them, which prevents the indoor temperature from stabilising and produces the sudden drops in warmth occupants notice and complain about.
An anti-freezing sensor at the base of the unit detects ice accumulation and manages protection automatically at low ambient temperatures.
Applications for the 6 kW Heat Pump
Domestic hot water with higher demand
This is where the 6 kW model earns its position in the range. At 8 kW of hot water heating capacity and 172 litres per hour with a COP of 4.3, it suits households where hot water is drawn heavily rather than occasionally. Two bathrooms in simultaneous morning use, or a family with a bath routine, are the cases where the extra capacity over the 5 kW unit is genuinely noticed.
Underfloor heating
The most efficient application, and the unit's figures show why. Underfloor heating performs at 30 to 45°C flow temperature, and at 35°C this model reaches a COP of 4.42 against 3.43 at 45°C. The 6 kW unit supplies low-temperature water to a manifold that splits flow between individual floor heating pipe loops, each controlled by a thermal actuator responding to its own room thermostat.
Radiator central heating
The unit can replace a gas or oil boiler feeding radiators. One caveat applies clearly from the specification: radiators sized for 70 to 80°C boiler water will demand high flow temperatures, and COP falls from 4.42 to 3.43 between 35°C and 45°C alone. Oversizing the radiators so they perform at lower temperatures preserves the efficiency benefit, and this should be assessed before conversion rather than discovered afterwards.
Summer cooling
The unit is reversible, delivering 5 kW of cooling capacity at A35/W7 with an EER of 2.85, a full kilowatt more than the 5 kW model. In markets with a genuinely hot summer, this additional cooling headroom is often the deciding factor between the two capacities.
Installation clearances affect performance, not just access. The outdoor unit needs unobstructed airflow on all sides to absorb and reject heat effectively, and restricting it reduces both output and efficiency. At 1075 × 480 × 805 mm and 70 kg, plan the mounting position and access route before delivery, and site the unit away from bedroom windows given its ≤54 dB(A) rating.
6 kW Compared with the Wider Range
| Parameter | 5 kW | 6 kW | 9 kW | 16 kW |
|---|---|---|---|---|
| Model | QB KFXFC-005SRI | QB KFXFC-006SRI | QB KFXFC-009SRI | QB KFXFC-016SRI |
| Heating range (kW) | 2.0–6.0 | 3.0–8.0 | 3.5–10.0 | 6.5–18.0 |
| COP at A7/W35 | 4.5 | 4.42 | 4.46 | 4.53 |
| Hot water capacity (kW) | 6 | 8 | 10 | 18 |
| Water yield (L/h) | 129 | 172 | 215 | 387 |
| Cooling capacity (kW) | 4 | 5 | 6.5 | 14 |
| Noise dB(A) | ≤52 | ≤54 | ≤55 | ≤56 |
| Water port | G3/4 DN20 | G3/4 DN20 | G1.0 DN25 | G1.0 DN25 |
| Net weight (kg) | 60 | 70 | 80 | 120 |
| Best suited to | 2–3 bedroom homes | Medium homes | Medium to large homes | Large homes, light commercial |
All four capacities share the same platform: R32 refrigerant, DC inverter twin rotary compressor, reversible heating and cooling, ERP A+++ at 35°C, operation to -35°C, and CE and RoHS certification. The 6 kW unit shares the G3/4 DN20 water connection and single-fan configuration with the 5 kW model, while the 9 kW and 16 kW step up to G1.0 DN25.
OEM and ODM Customization
Our team offers expert guidance and customization to suit your product needs. Prior to commitment, provide written confirmation of the key parameters: required heating and cooling capacity, cabinet colour, controller and connectivity requirements, and branding specification. We employ advanced modelling to ensure project confidence, and product development maintains strict confidentiality, safeguarding your project throughout.
Available customization covers cabinet colour across the eleven finishes shown above, logo and nameplate, packaging, and controller and operating parameter configuration for private-label supply. Samples are produced and performance tested against your specification before production commitment, and performance and leak test records are available for production batches. See the full OEM and ODM service for details, or read about our heat pump OEM factory and how the process works.
Frequently Asked Questions
What size house does a 6 kW heat pump heat?
A 6 kW unit generally suits a medium home with moderate heat demand, where the calculated heat load falls roughly between 4 and 7 kW. Floor area alone is not a reliable guide, because insulation quality, glazing, ceiling height, local climate, and hot water demand all affect the load. Its 3.0 to 8.0 kW modulation range means it covers a useful span, but note the 3 kW minimum: in a small, well-insulated property whose mild-weather demand sits near 2 kW, the unit would cycle rather than modulate, and the 5 kW model would perform better.
Should I choose the 5 kW or the 6 kW?
Choose the 6 kW if your calculated heat load sits between roughly 4 and 7 kW, or if domestic hot water demand is significant, since it produces 8 kW of hot water at 172 litres per hour against 6 kW and 129 litres per hour on the 5 kW. Choose the 5 kW if your load is nearer 3 to 4 kW, because its 2 kW minimum output modulates better through mild weather, and because it is marginally more efficient, quieter, and lighter. Oversizing is not a safe margin: a unit that cannot modulate low enough cycles instead of running steadily, which reduces efficiency and increases wear.
How efficient is the 6 kW heat pump?
It achieves a COP of 4.42 at A7/W35 test conditions, delivering 6 kW of heat from 1.36 kW of electrical input, and carries an ERP rating of A+++ at 35°C and A++ at 55°C. For domestic hot water the COP is 4.3. The efficiency you achieve in service depends most on flow temperature, and this unit's own data shows the effect clearly: COP falls from 4.42 at 35°C water to 3.43 at 45°C. Outdoor temperature and building insulation are the other two determining factors.
How much hot water does it produce?
The 6 kW unit delivers 8 kW of domestic hot water heating capacity at 172 litres per hour, with a COP of 4.3 and an input power of 1.86 kW. That is roughly 33% more hot water production than the 5 kW model, which is why the 6 kW is often specified for households with more than one bathroom in regular use. Actual delivery depends on the cylinder size, the incoming cold water temperature, and the target storage temperature, so confirm the full hot water arrangement with your installer.
Can it provide cooling as well as heating?
Yes. The unit is reversible and delivers 5 kW of cooling capacity at A35/W7 conditions with an EER of 2.85, running the same refrigeration cycle in the opposite direction. That is a full kilowatt more cooling than the 5 kW model. If the system feeds underfloor heating, note that radiant cooling requires attention to condensation risk, since surfaces cooled below the dew point attract moisture. This is manageable with correct control but belongs in the system design rather than added afterwards.
How noisy is the 6 kW heat pump?
The 6 kW unit is rated at ≤54 dB(A), two decibels above the 5 kW model, using a single low-noise axial fan with a brushless DC motor. Placement matters more than the rating alone: position the unit away from bedroom windows and avoid siting it in a corner where sound reflects off two surfaces. The DC inverter compressor helps here, since modulating output produces steadier sound than a fixed-speed unit repeatedly starting and stopping.
Will it work in a cold climate?
The unit is engineered to keep operating down to -35°C ambient, which covers the great majority of populated cold-climate regions. Output does decrease as temperature falls, which applies to every air source heat pump, so cold-climate projects should be sized against the local design temperature rather than the nominal rating. The intelligent demand-based defrost system matters here too, since frequent ineffective defrost cycles are what typically undermines cold-weather comfort in simpler units.
Why R32 rather than R410A?
R32 has a Global Warming Potential of 675 against R410A's 2088, just 32% of it. Its lower liquid density means a smaller refrigerant charge is needed for the same system, and the greater heat required to evaporate R32 means a smaller mass flow rate per unit and a higher COP. There is also a commercial consequence: high-GWP refrigerants face progressive restriction under the European F-Gas Regulation and equivalent rules elsewhere, which makes equipment charged with them harder and more costly to service over time.
What are the unit dimensions and weight?
The 6 kW unit measures 1075 × 480 × 805 mm (W × D × H) and weighs 70 kg net. Packing dimensions are 1165 × 530 × 925 mm. Water connections are G3/4 DN20, the same as the 5 kW model, with a water yield of 1.38 m³/h and a pressure loss of 25 kPa. Note that no expansion tank is included, unlike the 16 kW unit which includes a 5 litre tank, so allow for one in the system design. Plan the access route before delivery, since the unit is both taller and heavier than the 5 kW model.
What colours is the 6 kW heat pump available in?
Eleven cabinet finishes are available: white, white grey, grey, black, blue, green, red, yellow, gold, brown, and mocca. This range exists for two reasons. For OEM and private-label partners, cabinet colour is part of brand identity. For residential projects, the outdoor unit is often visible from a garden or terrace, and matching it to the building rather than accepting a default white is a meaningful specification option. Colour is one of the customization parameters available on OEM orders alongside logo, nameplate, and packaging.
Is the 6 kW model available for OEM supply?
Yes. OEM and ODM customization covers cabinet colour across eleven available finishes, logo and nameplate, packaging, and controller and operating parameter configuration for private-label supply. Samples are produced and performance tested against your specification before production commitment, and performance and leak test records are available for production batches. All projects are handled under confidentiality agreement. Contact the technical team with your target market and volumes to discuss terms.
What certification does it carry?
The unit is CE and RoHS certified and carries an ERP energy label rating of A+++ at 35°C and A++ at 55°C. CE confirms compliance with applicable European safety, electromagnetic compatibility, and low voltage requirements, and RoHS confirms restriction of hazardous substances in electronic components. Certification documentation is available on request for regulatory submission and procurement compliance. Confirm any additional market-specific requirements for your destination, since certification obligations depend on where the product is sold rather than where it is manufactured.