Heat pump noise is appearing more frequently as a project constraint. Planning conditions are becoming more specific, and noise assessments are being requested earlier in the design process. This article outlines why some common responses to noise constraints make things worse, and covers top-level approaches to managing noise without compromising performance.
Noise constraints take several forms. Planning conditions are the most common, restricting when plant can operate or setting noise limits at a defined receptor such as a neighbouring property boundary. Permitted development rules introduce their own thresholds. In some cases, constraints arise from negotiated agreements rather than formal conditions. The specifics vary, but the result is the same: the heat pump cannot always run when and how the building needs it to.
A common response is to derate heat pumps: reducing output to bring noise levels down. A derated unit produces less heat, so more units are added to compensate. More units running simultaneously produces more aggregate noise, often exceeding what a smaller number of full-output units would have generated.
Managing Noise: The Options
Product selection is the more straightforward starting point. Some heat pumps are significantly quieter than others at equivalent output. The DELTA range, for example, produces the following sound pressure levels (SPL) at maximum output:
Model | Capacity at -5°C (kW) | SPL @ 1m (dB(A)) | SPL @ 10 m (dB(A)) |
| DELTA-HP1 | 90 | 62 | 42 |
| DELTA-HP2 | 177 | 64 | 45 |
| DELTA-HP3 | 265 | 65 | 47 |
| DELTA-HP4 | 351 | 66 | 48 |
All figures at 60/30°C, -5°C ambient. SPL figures are average values around the heat pump with noise reduction fitted. Indicative values with no reflections.
Selecting a quieter unit reduces the burden on other acoustic measures, but is rarely sufficient on its own.
The more flexible approaches treat noise as a time-domain problem. Most constraints apply during specific periods, such as a planning condition restricting operation after certain hours. Outside those windows, the plant can run without restriction.
Significant thermal storage volumes are typically specified for other reasons: plant flexibility, peak management, grid tariff optimisation. They also make noise management straightforward. Run the heat pumps during unrestricted hours, charge the store, and draw from it when limits apply. Demand is decoupled from production, and the building is served continuously without the heat pumps running continuously.
Acoustic enclosures can reduce noise at source without affecting output. However, they introduce a trade-off: enclosures restrict airflow, and one that allows sufficient airflow for the heat pump to operate effectively may not reduce noise enough to meet the constraint. They are a useful tool, but not always a complete solution.
Hybrid energy centres, combining heat pumps with electric boilers, address the problem differently. Electric boilers are quiet and, being housed entirely within a plant room, their noise output is not a design consideration. During noise-restricted periods, the heat pump can step back while the electric boiler covers the load.
Where constraints are particularly severe, a heat network is worth considering. The energy centre can be sited away from dwellings or at a less sensitive point on site, delivering heat to consumers via the distribution network. The equipment still generates noise, but at a location where constraints are less onerous or absent altogether.
Noise management is a question of system design: product selection, storage strategy, plant configuration, and equipment location. Treating it as a specification problem (find the quietest unit, derate if necessary) addresses only part of the picture.
Future guidance will cover the technical side: sound power levels, receptor-based assessment, and where the rules are most commonly misapplied.
