Predicts the combined dB(A) sound pressure level a cluster of plant items produces at a
site boundary or neighbour's façade, and checks it against an entered background/planning limit.
Tender-stage only. Verify final design against an acoustic consultant's assessment.
For design guidance only. Always verify with a qualified acoustic consultant.
About this plant noise boundary check calculator
This free plant noise boundary check calculator predicts the combined A-weighted sound pressure level a cluster of plant items, air-source heat pumps, chillers, AHUs or condensers, produces at a stated distance, such as a site boundary or a neighbour’s façade, and checks it against the background or planning limit you enter. It is aimed at M&E designers, contractors and acoustic assessors making a tender-stage or planning feasibility check before a full acoustic assessment is commissioned. Everything runs in your browser. Nothing is uploaded.
How plant noise at distance is calculated
Each source’s sound power level (Lw) is propagated to the receiver by the ISO 9613-2-lineage point-source formula Lp = Lw − 20·log₁₀(d) − 11 dB for free-field (spherical) spreading, or −8 dB for a source on a hard surface (hemispherical). A level quoted at 1 m is first converted back to Lw by reversing the same formula, and multiple identical units add 10·log₁₀(n). Every source’s level at the receiver is then combined logarithmically, L = 10·log₁₀(Σ10^(Lᵢ/10)), before an advisory barrier attenuation is subtracted and a +3 dB façade reflection (BS 4142 / ISO 1996-2) is added. The predicted level is compared with your own limit; the MCS-020(a) domestic ASHP figure of 37 dB LAeq,5min (mandatory from 20 September 2025) is shown as context only, never applied automatically.
Frequently asked questions
Should I use spherical or hemispherical propagation?
Hemispherical (−8 dB) is the default and suits plant standing on or near a hard reflecting surface, the ground, a plinth or a roof. Which is the usual installation. Spherical (−11 dB) applies to a source radiating into free space with no nearby reflecting plane. The 3 dB difference is the energy reflected back from that surface.
Does it apply the MCS 020 limit for me?
No. MCS-020(a) is mandatory for domestic air-source heat pumps installed under Permitted Development from 20 September 2025 and sets a 37 dB LAeq,5min limit; the historical MCS 020 figure was 42 dB(A) at 1 m from a window. The calculator always compares against the boundary or background limit you enter, showing the MCS figures only as reference.
What barrier and façade corrections should I enter?
The advisory presets are 5 dB for a timber fence and 10 dB for a close solid barrier (subtracted as attenuation), and +3 dB for a receiver at a reflecting façade (added, per BS 4142 / ISO 1996-2). Both default to 0 so you only apply what the site justifies. Treat every result as tender-stage and confirm it with a qualified acoustic consultant.