NOTE This standard governs the construction-phase cleaning, high-velocity flushing, and chemical passivation of closed hydronic distribution systems, performed by the installing mechanical contractor after the piping passes its hydrostatic pressure test and before the system is balanced or placed in chemical service. (1.1)

NOTE Closed hydronic systems within scope include heating hot water (HHW), chilled water (CHW), dual-temperature, condenser water, and inhibited-glycol loops, in carbon steel, copper, or grooved-mechanical piping, at any system size. (1.2)

NOTE The work of this standard ends at acceptance of passivation and delivery of the signed cleaning, flushing, and passivation report; the ongoing chemical treatment program described in Hvac Water Treatment takes over from that point. (1.3)

NOTE This standard owns the construction-phase execution sequence the piping contractor works to. The pre-operational cleaning rationale and the long-term chemistry are owned by Hvac Water Treatment; the two are complementary and shall be read together. (1.4)

NOTE BSRIA BG 29 is cited as an industry reference guide for velocity selection, method-statement content, and acceptance criteria; it is not a mandatory compliance document on US projects. (2.3)

NOTE Action Submittals (3.1)

NOTE Action submittals establish the planned method before any chemical is brought to site, so the Owner and Engineer can confirm velocity feasibility, chemical compatibility, bypass arrangement, and discharge route in advance of the work. (3.1.1)

NOTE Specifying the cleaning scope only as a line item inside the piping section, with no method statement or acceptance criteria, lets subcontractors price the work without planning it. This standard requires a dedicated, reviewed method statement. (3.1.2)

NOTE Closeout Submittals (3.2)

NOTE The closeout submittals are the documentation baseline the Owner relies on for the water treatment program and for any future coil warranty claim; without them there is no evidence that cleaning was performed. (3.2.1)

NOTE Informational Submittals (3.3)

NOTE Responsibility Assignment (4.1)

NOTE Ambiguity over who performs the cleaning - the piping contractor, an Owner-furnished water treatment provider, or a specialty cleaning subcontractor - creates responsibility gaps and schedule conflicts with TAB and commissioning. The responsible party shall be named before the work begins. (4.1.1)

NOTE Coordination (4.2)

NOTE The flushing operation sits between three other trades, and the most common project failure is starting TAB or commissioning before flushing is accepted, which fouls coils that then must be back-flushed after balancing. (4.2.1)

NOTE Chemical Handling (4.3)

NOTE Pre-Cleaning System Condition (5.1)

NOTE Construction debris in a new hydronic system includes mill scale, weld spatter, cutting oils, thread-cutting lubricant, jointing compound, and general trash; the purpose of cleaning and flushing is to remove this material before it lodges in coils, exchangers, and valve seats. (5.1.1)

NOTE Copper oxide scale formed inside brazed joints made without a nitrogen purge flakes off during high-velocity flushing and recirculates into finned coil tubes, where it cannot be flushed out and causes sustained heat-transfer loss. (5.1.2)

NOTE System Type (5.2)

NOTE The cleaning chemistry, flush velocity target, and passivation temperature all depend on the system type and dominant metallurgy, which shall be identified before selecting the method. (5.2.1)

NOTE Filling (6.1)

NOTE The system is filled with clean make-up water and brought to fill pressure so that the pre-cleaning condition - leak-free and at a known baseline chemistry - is confirmed before any chemical is added. (6.1.1)

NOTE Sensitive Equipment Isolation (7.1)

NOTE Debris mobilized at flushing velocity damages coil tubes, scores control valve seats, and clogs plate heat exchanger channels. Routing flush flow through this equipment is the second most common cleaning failure, after premature TAB. (7.1.1)

NOTE Dead Legs and Branch Ends (7.2)

NOTE Debris accumulates in uncirculated sections and migrates back into the cleaned system once interconnecting valves are opened for service. Every dead leg and branch-end service needs a temporary jumper or end-of-line flush connection. (7.2.1)

NOTE Cleaning Method Selection (8.1)

NOTE The cleaning method is selected from the dominant contamination: an alkaline degreaser handles cutting oils and general construction soil on most new systems; trisodium phosphate (TSP) is a commodity alternative; an acid clean is reserved for heavy mill scale or weld discoloration; and a mechanical-only flush is acceptable for small all-copper systems. (8.1.1)

NOTE Alkaline Degreaser Parameters (8.2)

NOTE The alkaline degreaser is dosed into the filled system and circulated warm to lift cutting oils and construction soil into suspension before the mechanical flush carries them out. (8.2.1)

NOTE TSP Alternative Parameters (8.3)

NOTE Trisodium phosphate is restricted for sanitary discharge in some jurisdictions; where TSP is used, the discharge plan shall confirm acceptance before the clean begins. (8.3.1)

NOTE Flush Velocity (9.1)

NOTE The minimum flush velocity is the industry-consensus 5 ft/s for carbon steel; 6 to 8 ft/s is preferred and usually achievable in mains. The contractor demonstrates by calculation that every pipe section reaches the minimum, adding targeted jumpers at dead legs that the main flush cannot reach. (9.1.1)

NOTE Flush Pump Source (9.2)

NOTE System pumps are selected for design flow at design head, not for high-velocity low-head flushing, so on larger systems they cannot reach 5 ft/s with all valves open. An external high-volume flush pump is then required for the cleaning operation. (9.2.1)

NOTE Flush Color Monitoring (9.3)

NOTE Flush water is sampled at intervals at the flush drains and its color and clarity logged photographically; the trend from turbid to clear is the visible evidence that debris is being removed. (9.3.1)

NOTE Discharge Coordination (10.1)

NOTE Alkaline cleaner discharges can violate local sewer pretreatment limits, and acid-cleaner discharges almost always require neutralization or off-site disposal. The discharge route must be coordinated with the local authority before the clean begins, not after. (10.1.1)

NOTE Acceptance Criteria (11.1)

NOTE Flush acceptance moves from a visual clarity check, through field turbidity measurement, to laboratory analysis for total iron and total suspended solids, depending on the rigor the owner requires. Iron and TSS confirm debris removal; pH and conductivity returning near the make-up baseline confirm the cleaner itself has been rinsed out. (11.1.1)

NOTE Persistent total iron above 2 mg/L after multiple passes indicates an active corrosion source rather than construction debris, and shall be investigated before acceptance rather than flushed indefinitely. (11.1.2)

NOTE Passivation Timing (12.1)

NOTE Freshly cleaned carbon steel flash-rusts within hours in oxygen-bearing water, so passivation cannot wait. The inhibitor must be charged and circulation started the same day flush acceptance is achieved. (12.1.1)

NOTE Adding the long-term water treatment program at its normal operating concentration before passivation is complete will not build a dense passive film, because the operating concentration is too low; passivation deliberately runs at an elevated multiple of operating concentration. (12.1.2)

NOTE Passivation Chemistry (12.2)

NOTE Passivation chemistry must match the long-term water treatment program: molybdate, nitrite, or a molybdate-nitrite blend for carbon steel and mixed metallurgy, and a phosphonate-azole-polymer approach where aluminum is present. Choosing a passivation chemistry incompatible with the program forces a chemistry change at start-up. (12.2.1)

NOTE Passivation Circulation (12.3)

NOTE Carbon steel mains need a longer passivation circulation than copper-dominant systems to build the film; HHW systems are circulated warm toward operating temperature, while CHW and condenser water systems can only run at ambient with the pumps on. (12.3.1)

NOTE Coupon Installation (13.1)

NOTE Corrosion coupons are the physical evidence trail that passivation worked; without them there is no objective data to distinguish a well-passivated system from one whose chemical program is merely holding corrosion in check at higher ongoing cost. (13.1.1)

NOTE Glycol Charge Sequence (14.1)

NOTE On glycol loops the sequencing is explicit: clean and flush with water only, accept the flush, drain 100 percent of the flush water, then charge inhibited glycol at design concentration. Charging glycol into a dirty system embeds construction debris in the glycol where it cannot be flushed out without a full dump and re-clean, and cleaning with glycol in the system wastes expensive fluid and can degrade its inhibitor package. (14.1.1)

NOTE Automotive antifreeze shall not be used; its inhibitor package is not optimized for long-term hydronic service and its dyes and bittering agents interfere with field chemistry tests. (14.1.2)

NOTE System Reinstatement (15.1)

NOTE After flushing and passivation, the temporary bypasses come out and the protected equipment is returned to service; any temporary strainers must be removed or cleaned so they do not become a permanent restriction. (15.1.1)

NOTE Acceptance and Hand-Off (15.2)

NOTE The signed cleaning, flushing, and passivation report is the trigger that hands the system off to the water treatment provider and clears the TAB contractor to begin. (15.2.1)