Residential Heat Pump Sizing Guide: Selecting 3P, 4P, 5P, 6P, or 8P for Northern China Homes

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Short answer: Selecting the right residential heating heat pump size (3P, 4P, 5P, 6P, or 8P) depends on three building-specific numbers: the heat load in kW at the local design outdoor temperature, the heating distribution type (underfloor, fan coil, or radiator), and the available electrical service (single-phase 220V or three-phase 380V). For most well-insulated northern Chinese homes of 80 to 200 square meters, a 5P or 6P heat pump is the most common specification, with 8P reserved for larger homes, top-floor apartments, or buildings with underfloor distribution at design outdoor temperatures below -15 degrees Celsius.

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What does “3P / 4P / 5P / 6P / 8P” mean in residential heat pump sizing

In the Chinese residential heating market, heat pumps and air conditioners are commonly rated in “P” units (匹), which is shorthand for the cooling or heating capacity expressed in units of 735 W. A 3P unit is therefore rated at approximately 2.2 kW, a 5P unit at 3.7 kW, and an 8P unit at 5.9 kW. The same “P” rating used for cooling capacity translates to a similar order-of-magnitude heating capacity, though the actual heating output at the local design outdoor temperature depends on the unit’s heating-mode coefficient of performance and the outdoor temperature itself.

For residential heating applications, the right size depends less on the rated “P” number than on three factors that vary by building: the heat load in kW, the heat distribution system, and the electrical supply. Selecting the wrong size creates either comfort problems (undersized) or efficiency problems (oversized). The remainder of this article walks through the selection logic and provides a sizing table that Snowfairy’s application engineering team uses for residential project quotation.

Step 1 – Calculate the building heat load in kW

The first number to establish is the building heat load at the local design outdoor temperature. For most of northern China (Beijing, Tianjin, Hebei, Shanxi, Shandong, Henan), the design outdoor temperature is -7 to -12 degrees Celsius. For northeast China (Heilongjiang, Jilin, Liaoning, Inner Mongolia), the design outdoor temperature is -18 to -25 degrees Celsius.

A simplified rule for well-insulated modern residential buildings (post-2010 construction, double-glazed windows, external wall insulation, roof insulation):

Building type	Heat load estimate	Notes
Apartment, 80 to 100 m2, well insulated	4 to 6 kW	Two-bedroom urban apartment in post-2010 building
Apartment, 120 to 150 m2, well insulated	6 to 9 kW	Three-bedroom apartment or corner unit
Townhouse or small villa, 150 to 200 m2	9 to 13 kW	Two-story unit with floor-to-floor stairwell losses
Villa, 200 to 300 m2	13 to 20 kW	Larger villa with significant glazing
Villa or commercial space, 300+ m2	20+ kW	Consider commercial heat pump sizing, not residential
Older or poorly insulated building (pre-2000)	Multiply above by 1.3 to 1.6	Single-pane windows or uninsulated walls

For a detailed heat-load calculation, Snowfairy’s application team uses the heat-transfer coefficient method (K-value method) per GB 50176. A typical residential heat-load calculation sheet covers external walls, roof, floor, windows, doors, and infiltration losses. The simplified estimates above are sufficient for budgetary quotation; a detailed calculation should be completed before final equipment selection.

Step 2 – Select the right heating distribution type

The distribution system sets the maximum heating water temperature the heat pump must deliver, which in turn determines whether a residential heat pump or a higher-temperature cold-climate unit is required. The three common residential distribution types and their design water temperatures are:

Underfloor heating. Design water temperature 35 to 45 degrees Celsius. The most common choice for new northern China construction. Compatible with all Snowfairy residential heat pump models (3P through 8P) and with the cold-climate XHRFGW-H401AFN2D split system.
Fan coil units (FCUs). Design water temperature 45 to 55 degrees Celsius. Standard for retrofit of older buildings without underfloor piping. Requires a heat pump that delivers higher water temperature; the residential Snowfairy series supports this range.
Radiators or steel panel heaters. Design water temperature 55 to 65 degrees Celsius. Less common in new construction because of the higher water temperature requirement, but sometimes used in retrofits of older buildings that previously had coal-boiler radiator systems. For radiator applications, the cold-climate XHRFGW-H401AFN2D split system is the appropriate Snowfairy selection.

Step 3 – Confirm the available electrical supply

Snowfairy residential heating heat pumps are available in single-phase (220V / 50 Hz) and three-phase (380V / 50 Hz) versions. The choice depends on the building’s existing electrical service:

Single-phase (220V): Available in 3P, 4P, and 5P models. Suitable for apartments with single-phase service. Maximum current draw at full heating output is approximately 20 A, which requires a dedicated 25 A breaker and 4 mm2 copper wiring.
Three-phase (380V): Available in 5P, 6P, 8P, and the cold-climate XHRFGW-H401AFN2D. Suitable for villas, townhouses, and buildings with three-phase service. Lower current draw per phase; standard distribution for buildings above 200 m2.

If the building has only single-phase service and the calculated heat load is above 5 kW, the installation will require a service upgrade from the local utility, which adds cost and lead time. Snowfairy’s quotation team can flag this requirement during the project review stage.

Step 4 – Apply the sizing table

The Snowfairy sizing table combines heat load, distribution type, and electrical supply into a recommended model and configuration. For typical northern China residential projects (design outdoor temperature -7 to -12 degrees Celsius):

Heat load	Building size	Recommended model (underfloor)	Recommended model (fan coil)	Recommended model (radiator)
4 to 5 kW	80 m2 apartment	3P single-phase	3P single-phase	5P single-phase
5 to 7 kW	100 m2 apartment	4P single-phase	4P single-phase	6P three-phase
7 to 9 kW	130 m2 apartment	5P three-phase	5P three-phase	6P three-phase
9 to 12 kW	180 m2 townhouse	6P three-phase	6P three-phase	8P three-phase
12 to 18 kW	250 m2 villa	8P three-phase	8P three-phase	Cold-climate split (XHRFGW-H401AFN2D)
18 to 40 kW	400+ m2 villa	Cold-climate split (XHRFGW-H401AFN2D)	Cold-climate split	Cold-climate split

What changes for cold-climate regions (Heilongjiang, Jilin, Inner Mongolia)

In cold-climate regions where the design outdoor temperature is below -15 degrees Celsius, residential heat pumps face two additional constraints:

Reduced heating output at low temperatures. All air source heat pumps lose heating capacity as outdoor temperature falls. A standard 8P unit that delivers 8 kW of heating at +7 degrees Celsius may deliver only 5 kW at -15 degrees Celsius. For reliable heating in a 200 m2 well-insulated villa in Harbin, the XHRFGW-H401AFN2D cold-climate split system is the appropriate choice.
Lower heating COP at low temperatures. The coefficient of performance falls as outdoor temperature drops. A standard residential heat pump with COP 3.5 at +7 degrees Celsius may operate at COP 2.0 at -15 degrees Celsius. The cold-climate XHRFGW-H401AFN2D maintains COP above 2.0 down to -12 degrees Celsius per the China energy conservation standard.

Common sizing mistakes to avoid

Three mistakes appear repeatedly in residential heat pump quotations:

Sizing by “P” only, not by heat load. A 5P unit is not the right choice for every 100 m2 home. The 5P rating refers to cooling output under standard conditions; the actual heating output varies with outdoor temperature and the unit’s low-temperature heating curve. Always size by calculated heat load at design outdoor temperature.
Ignoring electrical service capacity. Selecting a 6P three-phase unit for an apartment with only single-phase 220 V service creates an installation that cannot be commissioned without a utility service upgrade. Confirm the available service before specifying the model.
Forgetting about domestic hot water. Some residential heat pump installations also produce domestic hot water (DHW) in summer or year-round. A unit sized only for space heating may be undersized when DHW demand is added. Snowfairy’s residential heat pumps include a DHW mode that can be activated by a three-way valve; the heating capacity must cover both space heating and DHW heating peak.

What Snowfairy provides for residential project quotation

Snowfairy’s application engineering team supports residential installers and homeowners with the following quotation process:

Heat-load calculation worksheet (Excel template) for distributor and installer use
Model-selection worksheet that maps heat load, distribution type, and electrical service to recommended Snowfairy model
Installation drawing templates for typical apartment and villa configurations
Type-test report and CCC certification for regulated Chinese domestic market
Pre-shipment factory testing and quality control records

For qualified inquiries, Snowfairy’s residential sales team can provide the model-selection worksheet, the heat-load template, and a sample quotation for a specific building. Distributor pricing is available on request.

Frequently asked questions

What is the difference between a 5P heat pump and a 5 kW heat pump?

A 5P unit is rated at approximately 5 times 735 W = 3.7 kW of cooling or heating capacity under standard rating conditions (outdoor +7 degrees Celsius for heating). A “5 kW heat pump” specification usually refers to the heating capacity at the local design outdoor temperature, which is often lower than the standard rating. Always compare specifications on the same rating basis.

Can a residential heat pump also provide cooling in summer?

Yes. The standard Snowfairy residential heat pump is reversible and provides both heating and cooling. In summer, the unit extracts heat from indoor air and rejects it outdoors, providing air conditioning. For buildings with both underfloor heating and fan coil units, the same heat pump serves both distribution systems year-round.

How long does it take to install a residential heat pump?

A typical installation takes 2 to 4 days, including: mounting the outdoor unit, mounting the indoor hydrobox, connecting refrigerant piping, connecting hydronic piping to the underfloor loops or fan coil units, connecting electrical service, and commissioning the system. A simple retrofit of an existing underfloor heating system is faster than a new-construction installation.

What government subsidies apply to residential heat pumps in 2024 and 2025?

Several Chinese provincial and municipal programs offer subsidies for residential heat pump retrofits that replace coal-fired boilers. The subsidy level varies by region, typically CNY 1,000 to 3,000 per household for residential sizes, and CNY 2,000 to 5,000 for cold-climate installations. Snowfairy’s sales team can provide the current subsidy list for a specific city or province on request.

What maintenance does a residential heat pump require?

Annual maintenance includes: outdoor coil cleaning, indoor filter cleaning or replacement, refrigerant leak check, electrical connection torque check, and hydronic water quality test. Snowfairy recommends a service contract with a local certified installer for residential customers; the typical annual service visit takes 1 to 2 hours.

Next steps for residential installer and homeowner evaluation

Installers and homeowners evaluating residential heat pump sizing for a specific building can request the model-selection worksheet, the heat-load template, and a sample quotation from Snowfairy’s residential sales team. The quotation request should include the building’s floor area, the year of construction, the type of distribution system, the electrical service specification, and the city or region. Snowfairy’s application engineering team returns a recommended model, a quotation, and an installation drawing within standard response windows.