Split or Monobloc Heat Pump: How to Choose
Split and monobloc are the two layouts of an air to water heat pump, and the choice between them shapes the installation, the servicing and the building work around the system. This article explains the difference in plain terms and helps a buyer decide which layout suits their project.
What split and monobloc actually mean
A split air to water heat pump has two main parts connected by refrigerant lines: an outdoor unit that holds the compressor and the outdoor coil, and an indoor hydraulic unit that holds the heat exchanger, pump and controls. Refrigerant travels between them, so the connection work is refrigeration work, done by a qualified refrigeration installer, with leak testing and charging as part of the job. A monobloc heat pump puts the whole refrigerant circuit in one outdoor unit and sends only water indoors through pipes. The indoor work is then plumbing work — pipes, pump, controls and the connection to the heating distribution — and no refrigerant handling is needed inside the building. That single difference drives most of the selection logic that follows, because it decides which trade does which part of the installation.
The building also feels the difference. A split system's indoor unit needs wall or floor space near the distribution manifold, and the refrigerant lines need a route from outside to inside that respects length limits and insulation needs. A monobloc system's outdoor unit needs space, a firm base, drainage and frost protection for the water circuit outside, and the water pipes need a route indoors that is insulated and protected. Neither layout is universally easier; each moves the difficult part of the job to a different place, and the right choice depends on which difficult part the local installation team handles best.
The listed models in this range
The listed range contains both layouts. The Aeolus split model covers 6 kW to 20 kW and is described for heating, cooling and domestic hot water, for residential and small commercial buildings, in the European market, with stable output stated at minus 25 degrees Celsius. The Deluxe monobloc models cover 4 kW to 16 kW single-phase and 12 kW and 16 kW three-phase, using R290 refrigerant. The split model's description-level presentation is worth noting: its listing carries no specification table, so a buyer interested in it should request the specification sheet as the first step. The monobloc models carry listed model ranges and supply figures, which makes their first comparison easier, though neither monobloc listing states a coefficient of performance or water temperatures, so those figures must also be requested.
A buyer comparing the two layouts should therefore compare them on installation and function first, and on listed figures second. The split model offers heating, cooling and domestic hot water in its description; the monobloc descriptions focus on heating. That functional difference may matter more than any kilowatt figure, because a building that needs summer cooling from the same system has a different requirement from a building that only needs heating. State the functions needed in the first inquiry, alongside the layout preference, and the reply can confirm which layout and which model matches.
Climate and the outdoor water circuit
Climate affects the two layouts differently. A split system's refrigerant lines are less exposed to frost than a monobloc's outdoor water circuit, because refrigerant does not freeze the way water does. A monobloc system in a cold climate needs frost protection for the water outside — antifreeze, drain-back, or continuous circulation strategies that the installer must design for the local design temperature. The Aeolus split description's minus 25 degrees Celsius statement is relevant here, because it describes stable output in cold conditions, but it belongs to the split model and should not be transferred to a monobloc in the same conversation. A cold-climate buyer choosing a monobloc should ask explicitly how the outdoor water circuit is protected at the local design temperature, and should treat that answer as part of the specification, not as an installation afterthought.
In warm climates the difference shrinks, because frost protection stops being the deciding factor and the choice turns on installer skills and indoor space. A warm-climate buyer with a strong plumbing team and limited indoor space may prefer a monobloc, while a buyer with a strong refrigeration team and a convenient indoor location for a hydraulic unit may prefer a split. Climate does not pick the layout by itself; it changes the weight of each factor.
Servicing and long-term ownership
Servicing also differs by layout. A split system needs a refrigeration technician for the refrigerant circuit and a heating technician for the water side, which can mean two trades for one system. A monobloc system needs a heating technician for most work, with refrigeration work concentrated in the outdoor unit, which can simplify the service arrangement. Spare parts follow the same split: a split system's indoor hydraulic parts and outdoor refrigeration parts come from different parts of the system, while a monobloc's parts are concentrated outdoors. A distributor should think about which service arrangement their network can support over the system's life, because a heat pump is a fifteen-to-twenty-year asset and the installation choice is also a servicing choice.
The ownership question that matters most is not which layout is better in general, but which layout the local team can install well and service for years. A well-installed monobloc beats a poorly installed split, and a well-installed split beats a poorly installed monobloc, whatever the catalogue says. Choose the layout the team can deliver, confirm the functions and the capacity step, request the specification sheet where the listing is description-level, and the layout decision will hold up over the system's life.