Designing for Acoustics and Sound Limits

Heat pump acoustics deserve a place in the first design discussion. The position of an outdoor unit affects the building layout, neighbouring homes and the way residents use their gardens. Leaving that decision until installation can restrict the available options.

For architects and specifiers, a successful design brings together product selection, siting, installation details and a clear assessment method. Each needs to be considered alongside the heating requirements.

Understand which sound figure you are reading

Two figures appear regularly in heat pump literature:

• Sound power level describes the sound emitted by the source. It is independent of the distance from the unit.

• Sound pressure level describes sound at a particular position. Distance and the surrounding environment affect it.

Both may be expressed in dB(A), so check the description and test conditions before comparing products. A figure measured or calculated five metres away cannot be substituted for a sound power figure.

The Kronoterm ADAPT 2 technical data sheet illustrates the distinction. For the ADAPT 2 M, it lists a declared sound power of 41 dB(A) and a maximum sound power of 55 dB(A), both at A7W35. That condition means an outdoor air temperature of 7°C and a leaving water temperature of 35°C.

The design team should confirm the correct input for its assessment with the manufacturer and assessor. Brochure figures need their operating conditions attached.

Establish the applicable sound limit

For domestic air source heat pumps using the permitted development route in England, MCS 020 a), Issue 1.1 sets out a calculation against 37 dB LAeq,5mins at the defined assessment positions, excluding the façade reflection effect.

These positions are one metre outside the centre of relevant doors or windows to neighbouring habitable rooms. The calculation must cover every potentially affected assessment position. A property boundary alone is insufficient.

The method accounts for sound power, distance, reflecting surfaces and qualifying barriers. It also addresses the combined contribution of two units. Low-noise-mode sound power must not be used for this calculation.

This is a specific assessment route. It is not a universal limit for every heat pump installation across the UK. Check the applicable national requirements and project planning conditions.

Passing the sound calculation is also only one part of establishing permitted development eligibility. The planning guidance published by Richmond Council demonstrates the wider checks involved, including unit size, the number of units, heritage constraints and installation position.

For projects requiring planning permission, agree the acoustic assessment scope with the local planning authority early.

Assess the location while the layout is flexible

Start with a plan showing candidate locations, neighbouring windows and the homeowner’s own bedrooms and outdoor seating areas. Include elevations where neighbouring windows are above ground level.

Compare the options before fixing service routes or landscaping. A location that appears discreet in an architectural elevation may be less suitable once its relationship with surrounding homes is understood.

The MCS guidance on mitigating heat pump noise recommends avoiding corners and enclosed spaces where sound can be amplified. It also highlights the importance of positioning units to minimise sound outside bedrooms and other habitable rooms.

Screening needs acoustic and mechanical review. A hedge or slatted fence should not be assumed to provide a calculable sound reduction. Any proposed barrier or enclosure must preserve the manufacturer’s airflow, safety and maintenance requirements.

Reserve enough space to resolve these details before the location becomes part of the tender package.

Coordinate acoustics with heating performance

Ask how the selected unit will operate at the project’s design conditions. Discuss space heating, hot water production and any proposed operating restrictions with the services designer.

A quiet mode may change the heating capacity available. If it forms part of the operating strategy, confirm that the building’s heating and hot water needs can still be met. Record the assumptions so later changes to controls can be reviewed.

For compact sites, several units or particularly sensitive surroundings, involve an acoustic consultant while alternative layouts remain available. Give them the proposed equipment, operating strategy and surrounding geometry, rather than a single headline noise figure.

Specify the installation details

Vibration can travel through supports and pipework into the building. The MCS mitigation guidance recommends appropriate anti-vibration mounts and consideration of structures that could transmit vibration.

Coordinate the base, supports and connections with the manufacturer. Include these details in the specification and drawings so the installer has a defined arrangement to follow.

For the Kronoterm ADAPT 2 range, request the current acoustic information for the selected model alongside its installation requirements. Review any proposed substitution against the same project criteria.

A useful acoustic specification should identify:

• The selected equipment and the source of its acoustic data.

• The approved location, orientation and supporting drawings.

• The assessment method, relevant positions and acceptance criteria.

• Any required barriers, mounting details or operating restrictions.

• Responsibility for checking changes and providing completion records.

Write measurable requirements. A description such as “quiet operation” leaves too much open to interpretation.

Check the completed installation

Before handover, confirm that the installed model, location, supports and screening match the assessed design. Review changes with the responsible designer and update the assessment where necessary.

Agree the verification process before installation, including whether site measurements are required and who will undertake them. Keep the acoustic assessment and any verification records with the handover information.

The government’s independent review of air source heat pump noise found a low incidence of complaints in the available evidence, with installation quality, location and proximity emerging as important factors. That supports a practical design approach: resolve the location and installation details early, then check that they have been delivered.

Bring acoustic design into the specification process

Acoustic performance is a project outcome. Product data provides the starting point; the layout, operating strategy and installation determine how that equipment fits its surroundings.

For your next project, contact KronoHP to discuss the selected Kronoterm model, its acoustic data and the information needed for specification.