The Challenges of Installing Air Source Heat Pumps in Older Properties

Air Source Heat Pumps (ASHPs) are an increasingly popular choice for heating homes due to their ability to harness renewable energy from the outside air, making them more sustainable than traditional fossil fuel-based heating systems.

However, when retrofitted to older properties with outdated insulation, glazing, and pipework, Air Source Heat Pumps (ASHPs) can become inefficient, reducing their overall performance and effectiveness.

Several factors contribute to this inefficiency when the heat pump is not integrated into a well-maintained, modernised home.

Insufficient Insulation

Proper insulation is essential for the optimal operation of an air source heat pump. ASHPs work by extracting heat from the air and transferring it into a property. However, in older properties with poor or outdated insulation, much of the heat generated can quickly escape through walls, roofs, and floors. This means that the heat pump has to work harder and consume more energy to maintain a comfortable temperature inside. The increased energy demand reduces the system's efficiency and raises running costs.

Old or Ineffective Glazing

Windows and glazing play a significant role in the thermal performance of a home. Older properties often have single-glazed windows or poorly insulated double glazing that cannot retain heat effectively. In such properties, much of the heat produced by the ASHP can escape through the windows, forcing the system to run more frequently and for longer periods to compensate. This reduces the overall efficiency of the heat pump and further contributes to higher energy consumption.

Outdated Pipework and Distribution Systems

In many older homes, the central heating pipework and radiator systems are designed to operate with high-temperature water, typical of older boilers. Air source heat pumps, however, are most efficient when operating with lower-temperature water (typically around 35–45°C), as they extract heat from the air at lower temperatures. Retrofitting a heat pump to an old radiator system that was built for high-temperature water means the radiators may not deliver enough heat at lower temperatures, leading to insufficient heating. As a result, the system may need to run longer to achieve the desired temperature, further increasing energy consumption and reducing efficiency.

Incompatibility with Existing Heating System

When retrofitting an ASHP into an older property, the integration with existing heating systems can be problematic. For example, if the property has an old, inefficient boiler system or an out-of-date hot water tank, these components might not be compatible with the low-temperature output of the heat pump. Without significant upgrades or modifications, the heat pump may struggle to meet heating demands, leading to higher running costs and lower system efficiency.

Thermal Mass and Building Fabric

Older properties tend to have a higher thermal mass, meaning they can absorb and store heat more effectively, but they also lose heat more slowly. In contrast, modern homes are often built with materials designed to limit heat loss. The combination of outdated materials and construction techniques in older properties can result in a mismatch with the way ASHPs operate, leading to inefficiencies in heat transfer and distribution.

Conclusion

While air source heat pumps can offer a sustainable and cost-effective heating solution, their efficiency is significantly impacted when retrofitted to properties with outdated insulation, glazing, and pipework. These factors can lead to increased energy consumption, higher operating costs, and an overall less effective heating solution. For air source heat pumps to perform optimally, older properties typically require comprehensive upgrades to their insulation, windows, and heating systems, ensuring compatibility with the heat pump's low-temperature requirements and reducing heat loss. Without these improvements, the overall efficiency of an ASHP system in an older home can be significantly compromised.