NOTE This Standard covers the design, materials, fabrication, and installation of condensate drainage piping that collects and conveys condensate generated by HVAC cooling and dehumidification equipment to an approved point of disposal. (1.1)

NOTE Condensate is the liquid water that forms when moist air contacts a cooling surface below its dew point. Every air-conditioning coil, evaporator, fan coil, chilled beam, and dehumidifier that operates below the entering-air dew point produces it continuously during the cooling season. The drainage system described here is the path that carries that water away under gravity, or by pump where gravity is not achievable, without overflow, nuisance discharge, or biological fouling. (1.2)

NOTE The work of this Standard includes primary drain piping, secondary (overflow) drain piping or equivalent overflow protection, drain pans and auxiliary pans, condensate traps, condensate lift pumps, overflow safety switches, pipe insulation where required, and the connection to the point of disposal. (1.3)

NOTE Condensate is classified as indirect waste under the plumbing code; the point of disposal and the receiving fixture are designed by the plumbing engineer. (1.4)

NOTE The boundary of this Standard is the connection to that receiving fixture — an indirect waste receptor, floor drain, hub drain, or other approved termination. The fixture itself, its trap, its vent, and the sanitary branch downstream belong to Sanitary Drainage Specialties. Coordination of the termination point is a shared obligation and is addressed in the Installation section. (1.5)

NOTE Refrigerant piping that may share a routing path or a support trapeze with condensate piping is specified in Refrigerant Piping and is not part of this Standard. (1.6)

NOTE Hydronic chilled water and condenser water distribution piping is specified in Hydronic Piping and Chilled And Condenser Water Piping; those systems are pressurized closed loops, not gravity drainage, and are governed by different material and pressure rules. (1.7)

NOTE Equipment that generates the condensate — fan coil units, VAV terminals with cooling, and makeup air units — is specified in Fan Coil Units, Variable Air Volume Terminals, and Makeup Air Units respectively; the internal drain pan furnished with that equipment is the equipment manufacturer's responsibility, and this Standard begins at the pan outlet connection. (1.8)

NOTE The locally adopted mechanical and plumbing codes govern; the International Mechanical Code is referenced here as the predominant model code, but the adopted edition and any state amendments (for example the California Mechanical Code) shall be verified for each project. (2.3)

NOTE Plenum-rated material is the single most common compliance failure on condensate work, so it is called out separately here and again under Materials. (4.3)

NOTE Standard Schedule 40 PVC is typically not listed under UL 2043 and is not permitted in a return-air plenum or other air-handling space. Inspectors routinely fail PVC found in plenums. Where any portion of a run passes through a plenum, that portion must be CPVC carrying the UL 2043 listing, or a listed metallic pipe. (4.4)

NOTE Condensate Temperature (5.1)

NOTE Condensate from standard comfort cooling leaves the coil at roughly 50 to 60°F, well within the service range of any candidate pipe material. The exception is equipment that can deliver warm or hot condensate to the drain — heat pumps in defrost, hot-gas defrost coils, and certain industrial dehumidifiers. PVC is limited to about 140°F continuous service; CPVC reaches about 200°F. Where elevated-temperature condensate is possible, CPVC or copper is required. (5.2)

NOTE Ambient and Condensation Control (5.4)

NOTE A cold condensate line in warm, humid, or unconditioned space will sweat exactly as the coil does, dripping secondary moisture onto ceilings, equipment, and finishes. This defeats the purpose of the drain. In high-humidity climates and in any unconditioned or below-dew-point space, the drain line is insulated to control surface condensation. (5.5)

NOTE Latent-Load Service (5.7)

NOTE Standard office and retail cooling produces roughly 0.5 GPH of condensate per ton at design conditions of 80°F dry bulb and 67°F wet bulb entering air. High-latent applications — natatoriums, commercial kitchens, laboratories, and dedicated dehumidification — can generate 1.0 to 1.5 GPH per ton or more. For these services, drain piping and pumps are sized from an explicit condensate flow calculation, not from the rule-of-thumb table. (5.8)

NOTE Material Selection (6.1)

NOTE Material is driven by three questions: does the run pass through a plenum, can the condensate be hot, and does the local code restrict plastics. Schedule 40 PVC is the default for non-plenum, standard-temperature runs — it is inexpensive, corrosion-proof, and universally available. CPVC is the default in plenums and wherever elevated temperature is possible. Type L copper and galvanized steel are used where metallic pipe is required by code or by an air-handling-space restriction that a plastic listing does not satisfy. (6.2)

NOTE Joints and Fittings (6.5)

NOTE PVC and CPVC are joined with solvent cement using the appropriate primer and cement for the material; PVC cement is not interchangeable with CPVC cement. Drainage fittings are used so the invert stays smooth and the slope is continuous through each fitting. Long-sweep fittings are preferred at direction changes to limit turbulence and solids deposit. (6.6)

NOTE Plenum Routing (6.9)

NOTE Where any portion of a drain run passes through a return-air plenum or other air-handling space, that portion is held to the air-handling-space material rule regardless of what the rest of the run uses. The transition from PVC to CPVC, where used, is made outside the plenum boundary. (6.10)

NOTE Minimum Size (7.1)

NOTE The drain connection from an equipment pan is never smaller than the pan outlet, and in no case smaller than 3/4 in. inside diameter. The line is then sized up for tonnage and for the number of units feeding a shared main. A frequent error is leaving a common main at 3/4 in. while several branches feed it — each added unit adds flow, and the main must grow accordingly. (7.2)

NOTE Sizing by Tonnage (7.5)

NOTE For a single unit on a gravity drain, the following sizes are a practical starting point at standard latent load: 3/4 in. serves up to about 20 tons, 1 in. serves about 21 to 40 tons, and 1-1/4 in. serves about 41 to 90 tons. These are confirmed against the sizing table in the adopted code edition and against the calculated flow for high-latent service. (7.6)

NOTE Slope (7.8)

NOTE Condensate moves by gravity, so the horizontal drain must fall continuously toward the disposal point. The code minimum is 1/8 in. per foot, a 1% grade. A steeper 1/4 in. per foot is preferred wherever ceiling space allows: it clears solids better, drains faster after a cycle, and needs cleaning less often. Slope is held through fittings, not just along straight pipe. (7.9)

NOTE Why a Trap, and Why Unit-Type Matters (8.1)

NOTE A draw-through air handler holds its drain pan under negative pressure — the fan pulls air across the coil and the pan sits on the suction side. Without a trap, that negative pressure holds the condensate in the pan and air is drawn up the open drain; the pan floods even though the line is clear. A liquid-seal trap deep enough to overcome the unit's static pressure lets the pan drain while blocking air infiltration. A blow-through unit, where the pan is on the discharge (positive-pressure) side, does not need a trap; adding one there only creates a stagnant pocket that breeds growth. The trap requirement is therefore unit-type specific. (8.2)

NOTE Trap Seal Depth (8.5)

NOTE The trap seal must be deeper than the unit's external static pressure expressed in inches of water column, or the negative pressure simply pulls the seal through. A unit at 1.0 in. WG external static needs at least a 2 in. seal; 3 in. is recommended to keep a margin and to survive evaporation between cycles. The trap is fitted with a cleanout so the seal can be cleared and re-primed. (8.6)

NOTE Why Secondary Protection Is Required (9.1)

NOTE A primary drain can and does block — algae, scale, a kinked pump line, a lost trap seal. When it does, the pan overflows. If that overflow reaches occupied space below, the result is ceiling and finish damage and a mold complaint. The code therefore requires a second line of defense on equipment where overflow could cause damage. Three methods are permitted, and the designer must choose and document one of them. (9.2)

NOTE The Three Permitted Methods (9.4)

NOTE The permitted methods are: a separate secondary (overflow) drain piped from a second pan outlet to a conspicuous point of disposal, where a visible discharge warns occupants of a primary blockage; a condensate overflow safety switch, a float device that detects rising water and shuts the associated HVAC unit down before the pan overflows; or an auxiliary drain pan installed beneath the equipment with its own independent drain to a conspicuous location. The switch is the most common choice on modern equipment because it stops the source rather than merely relocating the spill, but it requires a control connection that the electrical and controls scope must carry. (9.5)

NOTE Coordination of the overflow safety switch shutdown wiring between the mechanical and electrical drawings is a recurring miss; the switch is only protective if the control connection is actually made. (9.8)

NOTE Auxiliary Drain Pan (9.9)

NOTE Where an auxiliary pan is used, it is sized to catch the full footprint of the equipment plus a margin so that an offset leak is still caught. A pan that extends at least 3 in. beyond the equipment on all sides is the common rule. The pan is galvanized steel or molded polymer and drains independently of the primary line. (9.10)

NOTE When a Pump Is Required (10.1)

NOTE Gravity drainage is always the preferred and primary path; a pump is used only where the disposal point is above the equipment drain or too far away for the available slope — a basement air handler, a unit below the nearest hub drain, a long interior run with no fall. The pump is not a substitute for an undersized or under-sloped gravity line where gravity would have worked. Where a pump is required, the gravity portion upstream still complies with the size and slope rules. (10.2)

NOTE Pump Selection (10.5)

NOTE The pump is chosen from its curve at the actual static lift plus friction, with the design point taken at 2 to 3 times the equipment condensate generation rate to absorb peaks. The shut-off lift must exceed the required lift with a margin of about 20%. Single-unit light-commercial pumps typically deliver 80 to 120 GPH against 15 to 22 ft of lift on 120V; commercial collection stations reach 200 to 480 GPH against 30 to 65 ft on 120V, 230V, or 460V. The reservoir carries a float switch wired both to run the pump and to alarm and shut the unit down on high level. (10.6)

NOTE Pan Slope and Drainage (11.1)

NOTE A pan that holds standing water grows biofilm and degrades indoor air quality, which is why the ventilation standard requires the pan to slope to its outlet. The equipment-furnished pan must drain completely; field-set pans and auxiliary pans are pitched to their outlet at not less than 1/8 in. per foot. (11.2)

NOTE Support Spacing (12.1)

NOTE Plastic drain pipe sags between supports, and a sag becomes a low spot that holds water and collects solids — the same failure the slope is meant to prevent. Horizontal PVC and CPVC are supported at not more than 4 ft on center; vertical runs at not more than 10 ft. Metallic pipe follows the support table of the applicable plumbing code. Hangers do not crimp or restrict the pipe. (12.2)

NOTE Cleanouts (13.1)

NOTE Algae and mineral scale accumulate inside condensate lines and are the leading cause of blockage in humid climates. A drain that cannot be rodded or flushed will eventually fail. Cleanout access tees are provided on horizontal runs and at direction changes so the line can be cleared without cutting pipe. (13.2)

NOTE Drain-Line Treatment (13.4)

NOTE Slow-release algaecide tablets or pan strips suppress the biological growth that blocks drains. They are specified together with accessible maintenance points so the building operator can replace them. Treatment selection and placement are coordinated with the equipment and the maintenance plan. (13.5)

NOTE Point of Disposal (14.1)

NOTE Condensate is an indirect waste; it discharges to an approved receptor through an air gap, never with a direct connection to the sanitary system. The receiving fixture — an indirect waste receptor, floor drain, or hub drain — is provided under Sanitary Drainage Specialties and its location is coordinated with the plumbing engineer. The condensate line terminates above that receptor with the required air gap. (14.2)

NOTE Nuisance Discharge (14.5)

NOTE The code prohibits condensate discharge that creates a nuisance. Discharge onto a roof membrane, a walkway, a paved entry, or anywhere it can stain, ice, or pool is not acceptable and is a common rejection at inspection. Where an exterior termination is contemplated, it is confirmed as permitted locally and coordinated with the civil and architectural scope. (14.6)

NOTE Flow Test (15.1)

NOTE Each completed drain run is proven before concealment by pouring water into the pan or test point and confirming it flows to the disposal point without leaking, backing up, or pooling at any low spot. The trap is confirmed to hold its seal and to pass water. This catches reverse slope, missing primer, and crimped pipe while they can still be fixed. (15.2)

NOTE Overflow Device Test (15.5)

NOTE Every overflow safety switch is function-tested by raising the float and confirming that the associated HVAC unit shuts down. A switch that is wired but never proven is not protection. Secondary drains and auxiliary pan drains are confirmed clear to their conspicuous termination. (15.6)

NOTE General (16.1)

NOTE Installation follows the routing, slope, and support rules established above, with the run kept as short and direct as the architecture allows. The drain is installed so that it can be maintained — traps, cleanouts, and pumps reachable without cutting finishes. Coordination with adjacent trades is continuous, because the condensate line shares ceilings and chases with refrigerant, hydronic, and electrical work. (16.2)

NOTE Coordination with Other Trades (16.4)

NOTE Where condensate piping shares a routing path with refrigerant piping under Refrigerant Piping, the condensate line is positioned so that its support and any drip cannot penetrate or saturate the refrigerant line insulation. Shared trapeze supports are coordinated so neither system is crimped. The electrical and controls scope carries the overflow-switch and pump-alarm connections established in the Overflow Protection and Condensate Pumps sections. (16.5)

NOTE Connections to Equipment (16.8)

NOTE The drain connects to the equipment pan outlet with a union or other removable joint so the equipment can be serviced without destroying the drain. (16.9)

NOTE All condensate drainage materials shall be received, stored, and protected as follows: pipe, fittings, pumps, switches, and pans are delivered in the manufacturer's original packaging and stored under cover away from dirt, sunlight, and physical damage; solvent cement and primer are kept within the temperature range and shelf life printed on the container; PVC and CPVC pipe is shielded from prolonged direct sunlight to prevent ultraviolet degradation before installation. (17.1)

NOTE Condensate pumps and manufacturer-furnished pans carry the manufacturer's standard warranty; the installation is warranted against defects in materials and workmanship for one year from substantial completion. The warranty period and any extended-warranty option are as established in the project general conditions. (18.1)

NOTE Where condensate pumps are installed, spare float switches and a spare pump head or complete spare pump should be furnished for critical-service equipment so that a failed pump can be replaced without an extended outage. (19.1)