What Changed
On 29 May 2025, MCS 020(a) became mandatory for all air source heat pump installations under Permitted Development Rights in England. This update makes it easier to install heat pumps under PDR (1m boundary rule removed, larger units allowed), but stricter sound limits (37 dB vs 42 dB) mean installers who don't capture measurements correctly will face planning delays.
Why this matters: If MCS 020(a) sound calculations fail, installations require full planning permission (typically 8+ weeks). Accurate site measurements are essential to determine whether an installation can proceed under permitted development rights or requires planning permission.
- 1m boundary rule removed: heat pumps can now be installed within 1m of property boundaries (previously required 1m minimum distance)
- Sound limit lowered to 37 dB: calculated noise at each assessment position must be below 37 dB (previously 42 dB)
- Size limit increased to 1.5m³: heat pumps up to 1.5m³ now permitted under PDR (previously 0.6m³)
- Two heat pumps allowed: detached dwellings can install two units under PDR (previously one)
- Multiple assessment positions required: sound calculations must include all relevant neighbour positions, not just one
- Reflective surfaces counted: any surface (including ground, but not vegetation) within 1m of the heat pump affects sound calculations
The standard applies to England only. Scotland, Wales, and Northern Ireland remain under existing MCS-020 rules until further notice.
Why Installers Care
MCS 020(a) compliance is mandatory for Permitted Development installations. If the sound calculation fails (above 37 dB at any assessment position), the installation requires full planning permission, which delays the project and adds cost.
Callback risk: if site measurements aren't captured during the survey, installers may need to revisit the property to gather missing data for sound calculations.
Planning permission fallback: if the calculated sound level exceeds 37 dB, the installation cannot proceed under PDR. The homeowner must apply for full planning permission, which typically takes 8+ weeks.
Reflective surfaces impact: surfaces within 1m of the proposed heat pump location (walls, fences, paving, etc.) amplify sound. If these aren't identified during the survey, the calculation may fail later.
What's needed for MCS 020(a) compliance:
- Proposed heat pump location: exact position, distance from boundaries
- Neighbour assessment positions: windows, doors, habitable rooms facing the heat pump
- Reflective surfaces within 1m: walls, fences, paving, ground surfaces (not vegetation)
- Heat pump specifications: model, sound power level (LWA), operating modes
- Site measurements: distances to all assessment positions, boundary distances, reflective surface locations
If these measurements are captured during the survey, the sound calculation can be completed without revisits. If they're missing, the installer has to go back and measure again.
What to Capture on Site
For MCS 020(a) sound calculations, surveyors need to capture specific site measurements and document reflective surfaces during the heat pump survey:
- Proposed heat pump location: exact position, marked on floor plan and site photos
- Distance to property boundary: measured from proposed location
- Neighbour assessment positions: windows, doors, habitable rooms within audible range (marked on floor plan)
- Distance to each assessment position: measured from proposed heat pump location
- Reflective surfaces within 1m: walls, fences, paving, concrete, brick (excluding vegetation)
- Ground surface type: concrete, paving, gravel, grass (affects sound reflection)
- Proposed heat pump model: if known, for LWA reference
- Site photos: proposed location, neighbour positions, reflective surfaces
If the proposed heat pump location is confirmed on the day, surveyors should measure and document everything needed for MCS 020(a) compliance. If the location isn't finalised, potential positions should be noted and what measurements will be needed later should be flagged.
Industry Impact
MCS 020(a) represents a significant update to the standards for heat pump installations under permitted development rights. The changes make it easier to install heat pumps in many properties (removed boundary rule, larger units allowed), while ensuring noise levels remain acceptable to neighbours through stricter sound limits.
Typical survey turnaround for MCS 020(a) compliance includes:
- Survey pack + organised photos: available in portal immediately upon visit is completed
- Site measurements: proposed location, boundary distances, assessment positions, reflective surfaces
- Floor plan: marked with proposed heat pump location, neighbour assessment positions, reflective surfaces
- EPC: delivered by next morning
- Heat loss calculation: delivered the next day if required
We confirm whether MCS 020(a) sound calculations are required before booking, so installers know what to expect. If the proposed heat pump location isn't finalised before the survey, we note potential positions and provide guidance on what to measure later.
Common MCS 020(a) Failures
Based on installers we've worked with, here are the most common reasons MCS 020(a) sound calculations fail:
- Reflective surfaces not identified: walls, fences, or paving within 1m of the proposed location amplify sound, pushing the calculation over 37 dB
- Multiple assessment positions not checked: the calculation passes at one neighbour position but fails at another (all positions must be below 37 dB)
- Heat pump too close to neighbour windows: assessment positions with direct line of sight to the heat pump often exceed 37 dB
- Proposed location on hard surface: concrete or paving within 1m amplifies sound more than grass or gravel
- Heat pump model changed after survey: different models have different LWA ratings, which can push the calculation over 37 dB
By documenting reflective surfaces and measuring all assessment positions during the survey, we help installers spot potential failures before the calculation is submitted.
Related Resources
For more on MCS 020(a) compliance and heat pump survey requirements: