What is a monobloc air source heat pump

Green homes with monobloc heat pumps

A monobloc air source heat pump is a single, self-contained unit, installed on the outside of a residential property. Monobloc heat pumps comprise components required to draw thermal energy from the air and transfer that energy to the heating system and hot water cylinder within the dwelling.


The monobloc heat pump uses a refrigerant, a chemical capable of changing state between liquid and vapour, The heat pump unit contains:

  •  Evaporator
  •  Compressor
  •  Condenser
  •  Expansion valve


The evaporator is the heat exchanger that absorbs low-grade thermal energy and changes the state of the refrigerant from liquid to vapour. The compressor then uses electricity to increase the working pressure of the refrigerant. The condenser is a heat exchanger that rejects the heat into the wet system and changes the state of the refrigerant back to liquid. The expansion valve reduces the pressure of the refrigerant to start the cycle again.

Cross section of Dimplex monobloc heat pump System H


It is worth highlighting that there are several refrigerants that can be used, including fluorinated hydrocarbons such as HFCs and PFCs, or natural refrigerants such as propane. Each of these varies in toxicity and global warming potential (GWP). Advice on health and safety requirements and the environmental impact of refrigerants used should always be sought from individual heat pump manufacturers.

What are the key characteristics to consider when selecting a monobloc air source heat pump?

The key characteristics to consider when considering selecting a monobloc heat pump revolve around the physical size of the unit itself, its position, level of noise generation, kW output and ease of installation.


A monobloc air source heat pump ideally needs to be placed where it can easily connect to the proposed heating and hot water systems. However, it must also be in a position that provides sufficient airflow to the evaporator and, at the same time, does not compromise external access. If dwellings are close together, the acoustic performance of monobloc air source heat pumps should also be factored into specification decisions. Whilst the monobloc unit can be positioned up to 6m away from the dwelling, the extra pipe work increases cost and requires pipe insulation to limit heat loss from the hot water being supplied to the house by the heat pump.


As with all heat pumps, correct sizing of a monobloc heat pump and its hydronic design by a heating engineer should be carried out to best match the size, type and level of thermal performance of the dwelling with the output of the heat pump. Monobloc air source heat pumps are available in a range of kW outputs to match specification requirements, property size and heating demand.


As monobloc air source heat pumps are self-contained units with the refrigerant already in a closed loop system, installation can be done without the need to have an installer who has F-Gas qualifications. This broadens the choice of installers and makes the units easier to maintain and service once the project is finished and the dwellings are occupied.


If you would like to learn how the Dimplex range of monobloc air source heat pumps can meet your project requirements including hydraulic schematic advice and guidance on buffer vessels and water cylinders, as well as SAP10.2 modelling, please contact one of our presales team specialists.