How large is a heat pump and where does it need to be placed in terms of planning, connections and aesthetics?

The outdoor unit of an air-to-water heat pump is around 1m x 1m by 330mm deep. Ideally, it should be placed close to the house with the required clearances to allow good airflow. A spot with few plants nearby is best, as these could block the airflow around the unit and reduce its performance.
The installation of a single air source heat pump on domestic premises is a ‘permitted development’, so it does not normally require planning permission, if the installation complies with the Microgeneration Certification Scheme Planning Standards (MCS 020). Also, the heat pump must also be used only for heating purposes.
The permitted development rule applies to the installation of a new or replacement air-source heat pump for a house or block of flats (where the block consists solely of flats and does not include commercial premises).
It is a good idea to check with your local planning authority to ensure that all these limits and requirements will be met