BG29 in one line
BG29 is the BSRIA guide to pre-commission cleaning of pipework systems — the current edition is BG29:2021. It sets out how a new closed water system, typically the low-temperature hot water (LTHW) heating and chilled water (CHW) circuits in a building, should be cleaned and chemically treated before it is commissioned and handed over.
If a building has new wet heating or cooling, BG29 is almost certainly the standard the cleaning will be specified and judged against.
Why new pipework has to be cleaned
Installation leaves things behind inside the pipe — jointing compound, flux, cutting oils, swarf, dust and construction debris, plus whatever was in the fill water. Left in place, that debris drives corrosion, blocks valves, fouls heat exchangers and FCUs, jams control valves and gives microbiology somewhere to grow.
Pre-commission cleaning removes it, and then proves it has gone. That protects the plant, the warranty and the energy performance of the system for years.
What the process involves
In broad strokes: the system is filled, vented and pressure-tested, then dynamically flushed at velocity to carry debris out. That is followed by a chemical clean to lift oils and flux, a biocide wash to knock back microbiology, and finally dosing with a corrosion inhibitor to passivate the metalwork.
Samples are taken at each stage so the chemistry can be tracked — including the “iron plateau” test that confirms the chemical clean has done its job before the system is re-dosed and closed up.
How you prove it worked
BG29 sets acceptance targets — turbidity and suspended solids, dissolved iron and copper, microbiology such as TVC and sulphate-reducing bacteria, and inhibitor residual. Final acceptance samples are analysed by an independent, ideally UKAS-accredited, laboratory and checked against those targets.
The sampling itself is carried out to BS8552, and the ongoing chemistry once the system is in service is maintained to BSRIA BG50. BG29, BS8552 and BG50 are designed to be read together.
Who needs it, and when
Any new — or significantly altered — closed heating or chilled system should be cleaned to BG29 before it goes into use. It is routinely a main-contractor requirement, and it underpins manufacturer warranties and BREEAM credits.
The key is programme: cleaning sits right before commissioning, so it needs the system complete, filled and tested, and it needs an effluent discharge consent in place first — which can take weeks to obtain.
Where it tends to go wrong
The usual culprits are programme and readiness: leaving cleaning too late, systems that aren’t fully vented or pressure-tested on the day, missing flushing bypasses across the FCUs, sensitive plant left unprotected, and discharge consent not applied for in time.
Get those lined up early and pre-commission cleaning is straightforward. Leave them and it becomes the thing holding up handover.
How BWS helps
We deliver BG29 pre-commission cleaning on closed systems of every size, from single plant rooms to multi-floor towers, with UKAS-accredited acceptance sampling and a full evidence pack for handover.
If you have a system coming up to commissioning, send us the schematic and your programme dates and we’ll come back with scope and price.