Best practices for installing air source heat pumps

While every installation will have its own specific needs, there are considerations that apply to all air source heat pump (ASHP) installations, explains Steve Ellison, Assistant Training Manager at Grant UK:

As with any heating system, an air source heat pump installation follows a set of procedures which are detailed in the supporting Installation and Servicing Manual which engineers must follow. With a heat pump installation, the beginning of the process starts with the planning and thorough site surveys and assessments of the property and its heating and hot water requirements. Every home will have different requirements and it is important that installers work closely with their customers to ensure they specify and install a heat pump system which will fulfil their requirements. In this feature, we are going to explore some of the universal steps that apply to all ASHP installations.

Pre-installation Planning

Conducting detailed site surveys and room-by-room heat loss calculations are crucial. Discussing the customer’s requirements allows for the specification of the appropriate products needed for the system’s design.


Installation must adhere to the manufacturer’s instructions. ASHP installations often take longer than boiler replacements due to additional installation steps and system checks. It is essential to size and install new or replacement heat emitters correctly and ensure all system pipework is sized, fitted, and lagged properly. Comprehensive setup and commissioning of the heat pump and heating system are paramount.


The customer handover is critical. After successful installation and commissioning, installers should conduct a thorough handover with the customer, ensuring they understand and are confident in operating their new heating system.


When it comes to installing an air source heat pump, alongside the heat pump, accessories and core components needed for the system itself, engineers also need to remember the following:

Pipework insulation – insulating all internal and external system pipework with a suitable grade of insulation is vitally important. Grant UK supply a through wall insulation kit which includes heavy duty insulation to fit through the wall of the property and around the flexi hoses connected to Aerona³ heat pumps. If all system pipework is not suitably insulated, this will negatively impact the performance of the heating system.

Electrical wiring – the installation of a heat pump does involve the installation of electrical wiring so the installing engineer needs to be suitably trained and competent to complete these elements of the installation work or a qualified electrician may be required at various stages of the installation process.

Specialist access equipment – if a heat pump is being wall mounted, additional equipment may be required depending on the maximum installation height of the heat pump specified by the manufacturer. To facilitate safe working, equipment such as scaffolding and suitable ladders may be required. All Grant Aerona³ R32 heat pumps can be wall mounted at a safe height, with the top of the unit no more than two metres above ground level.


Prior to commencing an installation, installers should thoroughly assess the following:

Heat pump location – all heat pumps will make a noise and create a cold air discharge. It is important to discuss this potential nuisance factor with the end user when considering the final position of the heat pump. Take the proximity of neighbouring properties into account as well as the heat pump position when opening doors and windows on the customer’s own property.

Where possible, choose a position which is protected from the wind and where the unit will not obstruct access to doors or paths. The orientation of the heat pump should also be considered – to ensure maximum efficiency, ideally a heat pump should be positioned on a warmer side of the property, preferably on a south facing side.

Suitable installation base – an air source heat pump must also be installed on a firm, flat, level surface. The surface on which a heat pump is fitted must be able to support the weight of the heat pump unit and minimise the transmission of noise and vibration. If a suitable surface is not already in place, installers will need to prepare a suitable base for the heat pump prior to installation by either laying a flat trowelled concrete base 150mm thick or by positioning paving slabs on compacted hard core of sufficient depth.

Clearances around the heat pump – suitable clearances must also be in place around the heat pump. For Grant heat pumps, the recommended clearances are detailed in the Installation and Servicing Manual. These clearances are important because they allow for adequate air flow in and out of the heat pump while also making the heat pump easy to access for commissioning, servicing and maintenance.

Assessing the electrical system – when planning a heat pump installation, an assessment of the existing electrical system at the property should be undertaken to confirm its suitability. Furthermore, with every heat pump installation on a premises, there is a requirement to inform the relevant Distribution Network Operator (DNO). This can either be done via a DNO application (Apply to Connect) or a DNO notification (Connect and Notify). Grant’s Aerona³ 6kW, 10kW and 13kW heat pump models are DNO approved which means that installers can, in most instances, notify the DNO retrospectively within 28 days of installation. With heat pump units which are not DNO approved, an application must be made to the DNO before connecting the heat pump to the mains electrical supply.

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