MEP · 8 checks

Mechanical & HVAC
QA inspection checklist

HVAC and mechanical services quality audit.

Every check below carries what good looks like, when it passes, the standard it comes from and the defects that usually fail it. That guidance is what turns a tick-box into an inspection.

Ductwork

  1. 1.
    Duct sizes and routes match design
    What to look forDuct dimensions verified against M&E layouts and section drawings. Routes coordinated with structure and other services — no last-minute squeezes or kinks. Reducers gradual (≤ 22.5° angle of contraction). Branches at correct angles per design (typically 45°).
    Acceptable whenPer DW/144 (Specification for Sheet Metal Ductwork): pressure class A/B/C/D matched to design; sizes ±5 mm in any dimension; route within ±25 mm of design. CIBSE Guide B for design intent.
    StandardBESA DW/144:2016 — Specification for sheet metal ductwork. CIBSE Guide B2 — Ventilation and ductwork. CIBSE Commissioning Code A — Air distribution.
    Common defectsDuct downsized on site to fit ceiling void — flow restrictedSharp 90° bends instead of swept — high pressure lossBranches on wrong side of duct — turbulence, noiseReducers too steep — turbulenceDuct route changed without revised CFD — system imbalance
  2. 2.
    Joints sealed — no visible leaks
    What to look forFlanged or slip-and-drive joints sealed with mastic or duct sealant. Spiral duct joints sealed at couplers. No daylight visible at joints. Pressure test result available for the system class. Sealant continuous around full perimeter.
    Acceptable whenPer DW/143 (Ductwork Leakage Testing) and DW/144 pressure class: Class A leakage ≤ 0.027 L/s/m² @ 100 Pa; Class B ≤ 0.009; Class C ≤ 0.003; Class D ≤ 0.001. Pressure test results signed off before insulation.
    StandardBESA DW/143:2013 — Ductwork leakage testing. BESA DW/144:2016. CIBSE TM23 — air leakage.
    Common defectsLeakage test failed — sealant not applied to all jointsSealant smeared, not in joint groove — no sealTest taken with downstream end open — false passNo test certificate — Class assumed, not provenInsulation applied before test — defects hidden
  3. 3.
    Insulation complete and continuous
    What to look forThermal/acoustic insulation continuous along duct length, including bends, branches, and dampers. Joints butt-tight, seams taped or wired. Vapour barrier (foil facing) on outside, sealed at all joints. No exposed ductwork in unconditioned space. Class 0 / non-combustible material per spec.
    Acceptable whenInsulation thickness per BS 5422 / Approved Document L2A — typically 25-50 mm phenolic or mineral wool wrapped or rigid sectional. Reaction to fire Class 0 / A1/A2 in escape routes. Sealed vapour barrier (foil-faced glass tissue, taped joints).
    StandardBS 5422:2009 — Methods for specifying thermal insulation. Approved Document L (England/Wales). BESA TR/19 (cleanliness). DW/144 Section 30.
    Common defectsInsulation broken at hangers — thermal/acoustic bridgeVapour barrier torn around bends — condensationDamper bodies not insulated — frost / sweatingCombustible insulation in fire-rated routeJoints not taped — air bypass under insulation
  4. 4.
    Fire dampers at compartment boundaries
    What to look forFire damper at every duct penetration of fire-rated wall, floor, or ceiling. Damper body cast/built into the structure with manufacturer's installation kit (frame, refractory packing, retaining angle). Access panels in ductwork adjacent for testing. Drop-test mechanism / fusible link or motorised actuator linked to fire alarm.
    Acceptable whenPer BS EN 15650 / BS 9999 / Approved Document B: fire damper rated to match wall (E60, EI60, EI120 etc.). Installation per BS EN 1366-2 tested configuration. ASFP "Blue Book" guidance on installation. Drop-test access within 300 mm of damper.
    StandardBS EN 15650:2010 — Fire dampers. BS EN 1366-2:2015 — Fire resistance of dampers. BS 9999:2017. ASFP Blue Book — Fire-resistant ductwork. Approved Document B.
    Common defectsDamper installed in wrong wall (no fire rating) — no fire compartmentationRefractory packing missing — gap around damper body, fire bypassNo access panel — damper cannot be testedDrop test fails on completion — link tied or actuator deadDamper installed > 200 mm from wall face — outside tested config

Commissioning

  1. 5.
    Air flow rates balanced to design
    Record: Flow (l/s)
    What to look forFlow measured at every grille, diffuser, and main duct using calibrated anemometer or pitot/manometer. Balance dampers locked off after adjustment. Flow rates within tolerance of design at each terminal. Total system flow matches AHU duty.
    Acceptable whenPer CIBSE Commissioning Code A: ±10% on individual terminals; ±5% on main branches; total within ±5%. Velocity at supply diffusers within design (typically 2-4 m/s). Tolerance per BSRIA BG 49 — Domestic Ventilation Compliance Guide / BG 2 (commercial).
    StandardCIBSE Commissioning Code A:2020 — Air distribution. BSRIA BG 2/2010 — Commissioning air systems. NEBB / AABC procedures.
    Common defectsTotal flow short of AHU duty — leakage or fan curve issueFurthest terminals starved while near terminals over-supplied — no balance doneBalance dampers not locked off — drift after handoverNo commissioning record — cannot verifyWrong test method (handheld at face) gives unreliable readings
  2. 6.
    Room temperatures achieving set points
    Record: Temp (°C)
    What to look forEach room maintains design temperature (±1.5°C) under design load conditions. Test at peak summer/winter where possible, or under simulated load. No "hot/cold" complaints during witness test. Sensors calibrated and at correct height (typically 1.5 m AFFL).
    Acceptable whenPer CIBSE Guide A: occupied space ±1.5°C of set point under design conditions. CIBSE TM52 / TM59 for overheating. Soft-landings BSRIA BG 6/2014 — confirm performance over seasonal cycle.
    StandardCIBSE Guide A:2015 — Environmental design. CIBSE TM52:2013 — Limits of thermal comfort. BSRIA BG 6/2018 — Soft Landings.
    Common defectsSet point achieved but at full load — no marginSensor in direct sun or cold draft — false readingHot/cold spots in same room — air mixing inadequateSensor mounted too high (above 1.7 m) — stratified readingTest run during shoulder season — extremes not verified
  3. 7.
    BMS points connected and reading
    What to look forEvery plant item (AHU, FCU, valve, damper, sensor) connected to BMS with point list verified. Point names match design schedule. Live values reading correctly — temperatures, pressures, valve positions, status, alarms. Trend logging enabled.
    Acceptable whenPer BSRIA BG 4 (Specification for BMS): point-to-point test of all I/O. Sensor calibration verified within ±0.5°C / 5% RH. All alarms tested. Operator interface graphics complete. M&V dashboards ready.
    StandardBSRIA BG 4/2018 — BMS testing and commissioning. CIBSE Guide H — Building control systems. Approved Document L (M&V).
    Common defectsPoints connected but reading frozen — wiring intact but cabled to wrong I/OSensor not calibrated — reading off by 2-3°CAlarms set up but never testedGraphics show points that do not exist — virtual / dummyTrend logging disabled — no data for performance review
  4. 8.
    Commissioning report issued
    What to look forCommissioning report covering all systems with as-tested flow rates, temperatures, pressures, BMS point list, control narrative validation, witness signatures, and outstanding items. Issued via Building Manual / O&Ms. Soft Landings Aftercare period scheduled.
    Acceptable whenPer CIBSE Commissioning Code M and BSRIA BG 8 (Design Framework): full commissioning record per system. Final certificate signed by competent person. Aftercare obligations 1-3 years per Soft Landings.
    StandardCIBSE Commissioning Code M:2020 — Management. BSRIA BG 8/2009 — Commissioning Management. BSRIA Soft Landings Framework BG 54/2018.
    Common defectsReport missing entire systemsWitness signatures from contractor only — no client/CA witnessOutstanding items list still long at handover — defects rolled into AftercareNo control narrative validation — strategies not provenNo Soft Landings appointed — no seasonal recommissioning

Questions people ask

What is a mechanical & hvac QA inspection for?

To record that the work was checked against the specification before it was covered up or handed over: a pass or fail against each item, a measurement where one matters, and a photo where it failed. It is the evidence a client's quantity surveyor or clerk of works asks for, and the thing that settles the argument at final account.

What standards does this checklist check against?

Each item names its reference. On this checklist that includes BESA DW/144:2016, BESA DW/143:2013, BS 5422:2009, BS EN 15650:2010, CIBSE Commissioning Code A:2020, CIBSE Guide A:2015. The contract specification and the approved drawings always take precedence over a general standard; where they say something stricter, inspect to that.

Who signs a QA inspection off?

The person who carried out the check, named and dated, and where the contract calls for it the client's representative as a witness. The signature records that the check was done and what was found. It is not a warranty of the work.

How many items are on it, and do I have to use them all?

8 checks across 2 sections. Delete what does not apply to the job and add anything the specification asks for that is not here. A checklist that has plainly been thought about carries more weight than a long one nobody read.

Is this useful for a subcontractor as well as a main contractor?

More so. The subcontractor is the one who gets asked to come back and open something up. A signed inspection sheet with photos at the time is the cheapest insurance on a construction site.

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