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MEP Quick Calcs

Same formulas as MEP Design Platform – standalone, no project link. Type figures in for a quick on-site check.

All calculations follow relevant CIBSE / IHVE / Building Regulations methodology, but are provided for indicative purposes only. Always have a qualified engineer verify figures before use on a live project — this tool is not a substitute for a full design check.

Cold Water Storage

CIBSE/IHVE Plumbing Engineering Services Design Guide method: Storage Required = Daily Demand × Storage % (not peak-flow × hours – UK cisterns are primarily sized to cover a mains interruption, not smooth peak demand). Legionella check is a turnover calc: Selected Tank ÷ Average Hourly Demand, flagged if it exceeds 24 hours.

App default is 45 L/person (office figure). BS 6700 Table 1 (withdrawn, still widely cited – confirm against BS 8558/manufacturer data) gives higher institutional figures below.

Result

Daily Demand
Average Hourly Demand
Storage Required
Selected Tank (auto, standard sizes)
Turnover
Legionella turnover check (≤24hr)

Hot Water Storage

CIBSE Guide G Section 2 / CIBSE Journal CPD Module 74 method: Daily Demand → Peak Period Demand (editable fraction – not a published standard figure) → Storage Required (grossed up by the 80% usable-storage/stratification factor) → Required Reheat kW to recover the selected volume within the peak period.

App default: 40 L/person (office, no canteen). No CIBSE Guide G-attributed care home figure exists – enter a project-specific rate.
HSE ACOP L8/HSG274 minimum: 60°C

Result

Daily Demand
Peak Period Demand
Storage Required
Selected Storage
ΔT
Required Reheat
Storage ≥60°C (Legionella)
Covers peak demand

Pipe Sizing

CIBSE Guide C Haaland equation (Ch.4, Eq 4.5) for the Darcy friction factor – smallest standard size whose friction pressure drop is at or below your target rate.

Result

Selected Nominal Size
Velocity
Reynolds Number
Friction Factor (λ)
Pressure Drop

Pipe Insulation Condensation Risk

Checks an insulated pipe's outer surface temperature against the dew point of the surrounding air (BS 5422-style, radial/cylindrical resistance network) – CIBSE Guide C Table 3.25 film coefficients.

Surface Temperature
Dew Point
Margin
Min. thickness to clear dew point

Summer Overheating Quick Check

Indicative screening only, in the spirit of CIBSE TM59 / Part O – a weighted risk score from glazing exposure, fabric, ventilation and gains, calibrated against representative UK regional summer conditions. This does not model hourly weather, thermal mass or transient effects – it is not a dynamic simulation and not a substitute for a full TM59 assessment.

Sets a typical regional summer solar exposure factor, relative to the sunniest UK region. Indicative – use project-specific data if available.
Heavier, uninsulated fabric buffers peaks and loses heat faster overnight; well-insulated, low-mass construction tends to retain gains – a recognised TM59 risk factor, not an oversight.

Result

Glazing & solar exposure
Fabric & roof
Ventilation (mitigating)
Internal gains
Total indicative risk score
Risk band

TM52 Overheating Assessment (Commercial – Advanced)

Uses the real CIBSE TM52 adaptive-comfort formulas (running mean outdoor temperature, the three exceedance criteria) applied to actual hourly weather data via a simplified single-zone thermal model. This is a screening-grade engineering tool, not a validated dynamic simulation – it does not replace IES-VE / DesignBuilder / TAS for a real Part O or planning submission, and unless you upload a licensed CIBSE DSY file, the weather data is an illustrative representative profile, not official DSY data.

Generates an illustrative representative summer profile scaled for the region – for a real compliance submission, upload a licensed CIBSE DSY EPW file instead.

Room / space

Windows

Sets a typical g-value (solar heat gain) and U-value (conduction) together. g-value drives overheating risk far more than U-value – use Custom if you have exact manufacturer figures.

Result

Upload an EPW file or select a region profile to see results.
Criterion 1 – Hours of Exceedance (≤3%)
Criterion 2 – Daily Weighted Exceedance (≤6)
Criterion 3 – Upper Limit (never exceeded)
Peak operative temperature (assessment period)
Overall