A split heat pump divides the system into an outdoor unit holding the evaporator, fan and compressor, and an indoor hydrobox holding the condenser and hydraulics, connected by refrigerant lines. The water circuit stays entirely indoors, so it cannot freeze. Because refrigerant joints are made on site, an F-gas certified installer is required, and new air-to-water splits up to 12 kW must use sub-150-GWP refrigerants from 1 January 2027.
How does a split heat pump work?
A split heat pump separates the refrigerant circuit into two halves. The outdoor unit contains the fan, evaporator and compressor; insulated refrigerant lines carry hot compressed gas through the wall to an indoor hydrobox, where the condenser transfers heat to the heating water. The hydrobox typically also houses the circulation pump, expansion vessel, backup heater and controls — some models integrate a domestic hot water cylinder in the same cabinet.
Because only refrigerant crosses the building envelope, no water is ever exposed to outdoor temperatures. The two halves are joined on site by brazed or flared connections, then evacuated and charged — skilled work that determines the system's long-term reliability.
What is the difference between a split and a monoblock heat pump?
| Criterion | Split | Monoblock |
|---|---|---|
| What crosses the wall | Refrigerant lines | Heating water pipes |
| Frost risk | None — water stays indoors | Outdoor pipes need glycol or antifreeze valves |
| Installer qualification | F-gas certification required | Standard plumbing and electrical trades |
| Distance unit-to-plant room | Long refrigerant runs possible within manufacturer limits | Water runs kept short |
| Indoor space needed | Hydrobox on the wall or floor | Minimal |
A monoblock heat pump reverses the trade-off: factory-sealed refrigerant circuit, but water outdoors. The practical decision usually turns on climate, installer availability and plant room layout — see Monoblock vs split: which should you choose?.
Do split heat pumps need an F-gas certified installer?
Yes. Field-made refrigerant connections place split installation squarely inside the EU F-Gas Regulation's certification regime: only certified personnel may install, leak-check, service or decommission the circuit. The 2024 regulation tightens this further — EU-wide minimum training requirements, now covering natural refrigerants as well as F-gases, apply from 12 March 2026, and existing national certificates must be updated by 12 March 2027.
For building owners this is a checklist item, not a formality: an incorrectly evacuated or leaking line set silently costs efficiency for years, and leak-check obligations scale with the charge's CO2-equivalent.
Which refrigerants may split heat pumps use after 2027?
The EU F-Gas Regulation 2024/573 phases refrigerant options down in steps. From 1 January 2027, new air-to-water split systems up to 12 kW may not use refrigerants with GWP ≥150 — ruling out R32 (GWP 675) and R410A (GWP 2,088) in that class. Splits above 12 kW face a GWP 750 limit from 2029 and GWP 150 from 2033; a full F-gas ban for splits up to 12 kW follows in 2035. The backdrop is the HFC quota, cut to 42.9 Mt CO2e for 2025–2026 — roughly 48% below the 2023 level — which raises HFC prices well before the bans bite.
Manufacturers are responding with refrigerants under GWP 150, and with R290 designs where the A3 flammability rules can be met — easier in outdoor monoblocks than in indoor-connected splits.
When is a split heat pump the right choice?
Choose a split when hard frost and power cuts coincide (no water outdoors to freeze), when the outdoor unit must sit far from the plant room, or when an integrated indoor tower with DHW cylinder suits the layout. European buyers have plenty of company either way: heat pump sales reached 2.88 million units in 2025, up 13% year-on-year (EHPA).
Frequently asked questions
Can I install a split heat pump myself?
No. Making and charging the refrigerant connections legally requires F-gas certification in the EU, and manufacturer warranties assume certified commissioning. Hydraulic preparation can be done by any competent plumber; the refrigerant work cannot.
How far can the outdoor unit be from the indoor unit?
Manufacturer limits commonly allow line sets of 10–30 m with defined height differences. Longer runs need additional refrigerant charge and affect performance, so the limits in the installation manual are hard limits, not suggestions.
Is a split or a monoblock better for cold climates?
Splits hold one structural advantage: no water outdoors, so a power cut in a -20 °C week cannot burst pipes. Monoblocks manage the same risk with glycol or antifreeze valves. Both constructions heat equally well; cold-climate capacity depends on the compressor, not the split/monoblock choice.
Which refrigerant will replace R32 in small splits?
For new units up to 12 kW, the 2027 GWP 150 limit forces alternatives such as low-GWP HFO blends or R290 where the design meets flammability rules. Existing R32 systems remain legal to operate and service.