+---
+title: Refrigerant Piping
+category: Mechanical / Piping & Pumps
+toc_depth: 3
+description: >
+ When to use: Field-installed refrigerant piping (interconnecting tubing, or "line sets") serving split-system air conditioners and heat pumps, variable refrigerant flow (VRF) systems, and direct-expansion (DX) coils in commercial, institutional, and light-industrial buildings. Covers air-conditioning and refrigeration (ACR) copper tube selection by temper and type, brazed and refrigerant-rated mechanical joints, line sizing and routing within manufacturer length and lift limits, oil-return provisions and traps, closed-cell elastomeric insulation, A2L mildly-flammable refrigerant safety provisions under ASHRAE 15 and 15.2 (refrigerant detection, ventilation interlock, charge and concentration limits), penetration sleeving and firestopping, and the complete pressure-test, evacuation, and charging sequence. Applicable to systems using R-410A and the lower-GWP A2L refrigerants (R-32, R-454B) now mandated under the EPA AIM Act Technology Transition Rule.
+ Not intended for: Hydronic heating and cooling water piping (see [[sync/hydronic-piping]]); the air-conditioning and heat-pump equipment itself (see [[sync/variable-refrigerant-flow-systems]] and [[sync/split-system-air-conditioners]]); condensate drain piping; ammonia (R-717) industrial refrigeration and other systems governed by IIAR standards; supermarket CO2 (R-744) transcritical racks; or any refrigeration system with design temperatures below the ASME B31.5 scope. Factory-charged, factory-piped packaged equipment with no field refrigerant joints is excluded.
+---
+
+# Scope
+
+This specification covers the materials, fabrication, installation, examination, testing, evacuation, and charging of field-installed refrigerant piping that interconnects the components of split-system, variable refrigerant flow (VRF), and direct-expansion (DX) air-conditioning and heat-pump systems. The work includes the liquid, suction (vapor), and where applicable discharge and hot-gas lines; refrigerant specialties installed in the field piping; line insulation; pipe supports; sleeves and firestopping at penetrations; and the refrigerant safety provisions required for mildly flammable (A2L) refrigerants. All work shall comply with ASME B31.5, Refrigeration Piping and Heat Transfer Components, ASHRAE 15 and ASHRAE 15.2 for refrigeration system safety, the adopted edition of the International Mechanical Code (IMC), and the requirements of the equipment manufacturer whose system the piping serves.
+
+Refrigerant piping is unlike any other piping in a building. It is a sealed, high-pressure system that carries a two-phase fluid and a small but critical quantity of compressor lubricating oil that must circulate with the refrigerant and return to the compressor. The interior of the tube is a working surface: any moisture, oxide scale, particulate, or non-condensable gas left inside becomes a permanent contaminant that degrades capacity, attacks the compressor, and shortens equipment life. For this reason, the way the piping is brazed, pressure-tested, evacuated, and charged is as much a part of this standard as the materials themselves. A mechanically perfect installation that was brazed without a nitrogen purge, or charged without a proper evacuation, is a defective installation.
+
+The boundary of work under this standard is the refrigerant tubing and field-installed specialties from the service-valve or stub connection at the outdoor (condensing or heat-recovery) unit, through all interconnecting piping, branch joints, and headers, to the service-valve or stub connection at each indoor unit, fan-coil, or DX coil. The air-conditioning and heat-pump equipment itself, its factory charge, and its internal piping are covered by the equipment standards [[sync/variable-refrigerant-flow-systems]] and [[sync/split-system-air-conditioners]]. Electrical power and control wiring between units is covered by the electrical standards. Condensate drainage from indoor units and coils is not part of this standard.
+
+# Referenced Standards
+
+Materials, fabrication, and installation shall comply with the latest adopted editions of the following standards and codes. Where the contract documents, the adopted building or mechanical code, the equipment manufacturer's installation instructions, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing. The equipment manufacturer's published line-size, length, and elevation (lift) limits are mandatory and shall not be exceeded even where this standard or the drawings would otherwise permit it.
+
+| Standard | Title |
+|----------|-------|
+| ASME B31.5 | Refrigeration Piping and Heat Transfer Components |
+| ASME Sec. IX | Boiler and Pressure Vessel Code — Welding, Brazing, and Fusing Qualifications |
+| ASME B16.22 | Wrought Copper and Copper Alloy Solder-Joint Pressure Fittings |
+| ASME B16.50 | Wrought Copper and Copper Alloy Braze-Joint Pressure Fittings |
+| ASHRAE 15 | Safety Standard for Refrigeration Systems |
+| ASHRAE 15.2 | Safety Standard for Refrigeration Systems in Residential and Light-Commercial Applications |
+| ASHRAE 34 | Designation and Safety Classification of Refrigerants |
+| ASTM B280 | Seamless Copper Tube for Air Conditioning and Refrigeration Field Service (ACR) |
+| ASTM B88 | Seamless Copper Water Tube |
+| ASTM B819 | Seamless Copper Tube for Medical Gas Systems (where oxygen-clean tube is referenced) |
+| ASTM C534 | Preformed Flexible Elastomeric Cellular Thermal Insulation in Sheet and Tubular Form |
+| ASTM E84 | Surface Burning Characteristics of Building Materials (flame spread / smoke developed) |
+| AWS A5.8 | Specification for Filler Metals for Brazing and Braze Welding |
+| UL 60335-2-40 | Household and Similar Electrical Appliances — Particular Requirements for Electrical Heat Pumps, Air-Conditioners, and Dehumidifiers |
+| NFPA 70 | National Electrical Code (for refrigerant detection system and interlock wiring) |
+| IMC | International Mechanical Code (Refrigeration) |
+| MSS SP-58 | Pipe Hangers and Supports — Materials, Design, Manufacture, Selection, Application, and Installation |
+| EPA 40 CFR Part 84 | Technology Transition rule under the AIM Act (refrigerant GWP limits) |
+
+# Submittals
+
+## Action Submittals
+
+The Contractor shall submit the following for the Engineer's review and return before procurement and installation. Submittals shall be complete and internally coordinated with the equipment manufacturer's installation requirements before any item is submitted.
+
+- Product data for ACR copper tube, showing the ASTM B280 designation, temper (hard-drawn or annealed), type, outside diameter and wall thickness by line, and confirmation that the tube is supplied cleaned, dehydrated, nitrogen-charged, and capped
+- Product data for all fittings and joints, including wrought copper braze-joint fittings (ASME B16.50) and any refrigerant-rated mechanical or press fittings proposed, with the manufacturer's pressure rating and refrigerant compatibility (including A2L listing where applicable)
+- Product data for brazing filler metal, showing the AWS A5.8 classification (BCuP or BAg series), composition, and flux requirement
+- Product data for refrigerant-line insulation, showing the ASTM C534 type/grade, wall thickness, thermal conductivity, water-vapor permeability, maximum service temperature, and ASTM E84 flame-spread and smoke-developed indices
+- Product data for field-installed refrigerant specialties (filter-driers, sight glasses, service valves, ball valves, line-set isolation or shutoff valves) where part of the field piping scope
+- Product data for the refrigerant detection system (RDS) sensors and the ventilation/shutoff interlock components where A2L mitigation is required, with the alarm set point relative to the lower flammability limit (LFL) and UL 60335-2-40 listing
+- A refrigerant piping coordination drawing set showing routing, line sizes, equivalent lengths, vertical separations (lifts and drops), oil-trap locations, branch/header locations, support locations, and penetration and firestop locations, coordinated against the manufacturer's maximum allowable pipe lengths and elevation differences
+- The equipment manufacturer's refrigerant piping design tables or selection software output documenting that the proposed line sizes and lengths are within the allowable limits for the specific equipment and refrigerant
+- Brazing procedure specifications (BPS) and procedure qualification records (PQR) per ASME Section IX, and brazer performance qualification records for all personnel who will braze on this project
+- A written pressure-test, evacuation, and charging plan describing the test medium, hold pressures, hold durations, vacuum target, decay-test criteria, charging method, and the sequence relative to insulation and closing of penetrations
+- An A2L refrigerant safety plan (where the system uses an A2L refrigerant) documenting the system refrigerant charge, the smallest occupied space served, the calculated refrigerant concentration limit (RCL) compliance, and the mitigation provisions
+
+```datasheet
+label: Action Submittals Required
+type: checkbox
+options:
+ - "ACR copper tube product data (ASTM B280, temper, type, sizes)"
+ - "Fitting and joint product data (braze and mechanical)"
+ - "Brazing filler metal product data (AWS A5.8)"
+ - "Refrigerant line insulation product data (ASTM C534)"
+ - "Field refrigerant specialty product data (driers, valves, sight glass)"
+ - "Refrigerant detection system / interlock product data (A2L)"
+ - "Refrigerant piping coordination drawings"
+ - "Manufacturer line-sizing and length/lift verification"
+ - "Brazing procedure and brazer qualification records"
+ - "Pressure-test, evacuation, and charging plan"
+ - "A2L refrigerant safety / RCL compliance plan"
+default: "ACR copper tube product data (ASTM B280, temper, type, sizes)"
+```
+
+## Closeout Submittals
+
+At substantial completion, the Contractor shall provide the following before the refrigerant systems are accepted.
+
+- Signed and dated pressure-test reports for each circuit, recording the test medium (dry nitrogen, or nitrogen with trace refrigerant for leak location), the hold pressure on the high and low sides, the hold duration, the temperature-corrected pressure observations, and the pass/fail determination
+- Signed and dated evacuation reports recording the final vacuum achieved (in microns), the micron-rise (decay) test result after isolation from the vacuum pump, and the time held
+- Charging records documenting the refrigerant type, the total charge weighed into the system (factory charge plus field-added charge for line length), and the basis for the line-length charge adjustment per the manufacturer's instructions
+- As-built piping drawings reflecting actual routing, line sizes, equivalent lengths, oil-trap locations, and the location of each field-installed specialty
+- Operation and maintenance data for field-installed specialties and for the refrigerant detection system, including sensor calibration interval and end-of-life replacement date
+- A completed A2L mitigation commissioning record (where applicable) demonstrating that detection, alarm, and ventilation/shutoff interlock function as designed
+
+# Quality Assurance
+
+## Code Compliance
+
+All refrigerant piping shall comply with ASME B31.5 for design pressure, materials, joints, fabrication, examination, and testing, and with ASHRAE 15 (or ASHRAE 15.2 for residential and light-commercial applications) for system safety, refrigerant quantity limits, and piping in or through occupied spaces. The Contractor shall maintain a copy of ASME B31.5 and the applicable ASHRAE safety standard at the project site throughout installation.
+
+## Brazer Qualifications
+
+Personnel performing brazed refrigerant joints shall be qualified under ASME Section IX for the brazing procedure, position, and tube configuration being brazed. Qualification records shall be available at the site. The Contractor shall not allow unqualified personnel to make production joints; rework of joints made by unqualified personnel is at the Contractor's expense. Where a brazer has not performed qualified brazing within six months, requalification shall be required before production work.
+
+## Examination of Brazed Joints
+
+Each completed brazed joint shall be visually examined before it is insulated or otherwise made inaccessible. A satisfactory joint shows a continuous, uniform fillet of filler metal completely around the circumference of the socket, with the filler metal visibly wetted to both members. Joints showing incomplete fill, voids, blowholes, or evidence of overheating (firescale, eroded base metal) shall be cut out and re-made. Visual examination does not replace the pressure test; both are required.
+
+## Installer Qualifications
+
+The Contractor performing refrigerant piping work shall hold a current EPA Section 608 certification for refrigerant handling and shall have documented experience installing field-piped refrigerant systems of comparable type and scope. Personnel handling A2L refrigerants shall additionally have completed training on the safe handling, leak mitigation, and tool requirements specific to mildly flammable refrigerants.
+
+# Environmental and Service Conditions
+
+## Refrigerant and Safety Classification
+
+The refrigerant type is determined by the equipment selected and shall be as scheduled. The refrigerant safety classification (ASHRAE 34) governs the safety provisions required under ASHRAE 15 and 15.2 — most significantly whether the refrigerant is A1 (lower toxicity, nonflammable, e.g., R-410A) or A2L (lower toxicity, mildly flammable, e.g., R-32, R-454B). Under the EPA AIM Act Technology Transition Rule, most new comfort-cooling equipment manufactured in or after 2025 uses an A2L refrigerant with a global-warming potential below the regulated limit, so A2L provisions apply to the majority of new systems.
+
+```datasheet
+label: Refrigerant
+type: select
+options:
+ - "R-454B (A2L) — low-GWP, common in new split and packaged equipment"
+ - "R-32 (A2L) — low-GWP, common in VRF and ductless equipment"
+ - "R-410A (A1) — legacy nonflammable, existing-system service and replacement only"
+default: "R-454B (A2L) — low-GWP, common in new split and packaged equipment"
+```
+
+```datasheet
+label: Refrigerant Safety Classification (ASHRAE 34)
+type: radio
+options:
+ - "A2L — mildly flammable (R-32, R-454B); ASHRAE 15/15.2 A2L provisions apply"
+ - "A1 — nonflammable (R-410A); standard provisions apply"
+default: "A2L — mildly flammable (R-32, R-454B); ASHRAE 15/15.2 A2L provisions apply"
+```
+
+## Design Pressures
+
+Refrigerant piping shall be designed for the system design pressures established by ASME B31.5 for the refrigerant and the highest temperature the piping will experience on each side. The high-side and low-side design pressures shall be not less than the equipment manufacturer's stamped maximum allowable pressures. ACR copper tube of the selected type and wall is rated well above these pressures; the design-pressure requirement governs the selection of fittings, valves, and any field-installed specialties, which shall each be rated for the high-side design pressure unless they are isolated to the low side.
+
+```datasheet
+label: High-Side Design Pressure
+type: range
+unit: psig
+drawing_ref: true
+options:
+ min: 400
+ max: 700
+ setpoints: [400, 450, 500, 550, 600, 650, 700]
+default: 550
+```
+
+# Materials
+
+## ACR Copper Tube
+
+Refrigerant piping shall be seamless copper tube manufactured for air-conditioning and refrigeration field service in accordance with ASTM B280. ACR tube is supplied internally cleaned, dehydrated, charged with a holding pressure of dry nitrogen, and capped at both ends to keep the bore clean and dry until the moment of installation. The Contractor shall keep tube capped and pressurized until immediately before brazing and shall cut, ream, and braze each length without leaving the bore open to ambient air any longer than necessary. Plumbing-grade Type L tube to ASTM B88 is not interchangeable with ACR tube for this work because it is sized by nominal pipe size rather than actual outside diameter and is not supplied clean, dry, and capped; ACR tube to ASTM B280 (sized by actual OD) shall be used.
+
+```datasheet
+label: Copper Tube Standard
+type: radio
+options:
+ - "ASTM B280 ACR copper tube — cleaned, dehydrated, nitrogen-charged, capped (standard)"
+ - "ASTM B280 ACR copper tube, oxygen/medical-clean (where specified for critical systems)"
+default: "ASTM B280 ACR copper tube — cleaned, dehydrated, nitrogen-charged, capped (standard)"
+```
+
+```datasheet
+label: Copper Tube Temper and Form
+type: radio
+options:
+ - "Hard-drawn straight lengths for runs larger than 7/8 in. OD and all exposed/rigid routing; annealed (soft) coil line set for sizes through 7/8 in. OD where bending is required"
+ - "Hard-drawn straight lengths throughout (all sizes), with elbows and offsets made from fittings"
+ - "Annealed (soft) coil line set throughout (small split systems, short runs)"
+default: "Hard-drawn straight lengths for runs larger than 7/8 in. OD and all exposed/rigid routing; annealed (soft) coil line set for sizes through 7/8 in. OD where bending is required"
+```
+
+Hard-drawn (drawn-temper) tube is stiffer and stronger and holds a straight line with fewer supports, making it the standard for larger sizes, long mains, risers, and exposed routing. Annealed (soft-temper) tube is supplied in coils ("line set") and can be bent by hand or with a bender, which suits the short, flexible runs typical of small split systems and the final connections to indoor units. Annealed tube shall be bent with a forming tool or spring to avoid kinking; a kinked or flattened tube restricts flow and oil return and shall be cut out and replaced. Soft tube shall not be used for long unsupported runs where it would sag and trap oil.
+
+## Joints and Fittings
+
+Brazed joints shall use wrought copper braze-joint fittings conforming to ASME B16.50 (or solder-joint fittings to ASME B16.22 used in the braze configuration). Where the system design and the refrigerant manufacturer's listing permit, refrigerant-rated mechanical or press fittings that are listed for the refrigerant (including A2L where applicable) and rated for the high-side design pressure may be used in lieu of brazing at locations where open-flame work is restricted. Flare joints may be used only at equipment service connections that are designed for flare fittings and shall be made with a refrigeration flaring tool to the correct flare angle and torque.
+
+```datasheet
+label: Primary Joining Method
+type: radio
+options:
+ - "Brazed throughout, with dry-nitrogen purge (standard)"
+ - "Brazed mains; refrigerant-rated press/mechanical fittings where open flame is prohibited"
+ - "Flare connections at equipment, brazed elsewhere"
+default: "Brazed throughout, with dry-nitrogen purge (standard)"
+```
+
+## Brazing Filler Metal
+
+Brazing filler metal shall conform to AWS A5.8. For copper-to-copper joints, a phosphorus-bearing copper alloy of the BCuP series (typically BCuP-2 through BCuP-6, with a silver content as required for the joint clearance) shall be used; BCuP filler is self-fluxing on copper-to-copper joints and requires no flux. For copper-to-brass or copper-to-bronze joints (such as at service valves), a silver alloy of the BAg series shall be used with the appropriate brazing flux. Cadmium-bearing filler metals shall not be used. Where flux is used, all flux residue shall be removed after brazing because it is corrosive.
+
+```datasheet
+label: Brazing Filler Metal
+type: radio
+options:
+ - "BCuP series (phosphorus-copper) for copper-to-copper joints, no flux (standard)"
+ - "BAg series (silver alloy) with flux for copper-to-brass/bronze joints (service valves)"
+default: "BCuP series (phosphorus-copper) for copper-to-copper joints, no flux (standard)"
+```
+
+## Refrigerant Line Insulation
+
+Suction (and where present, any cold) refrigerant lines shall be insulated with preformed flexible elastomeric cellular (closed-cell) insulation conforming to ASTM C534. Closed-cell elastomeric insulation is used because it is itself a continuous vapor retarder: a refrigerant suction line runs well below the ambient dew point, and an open-cell or breached insulation will sweat, drip, and corrode. The insulation shall have a flame-spread index of 25 or less and a smoke-developed index of 50 or less per ASTM E84 for installation in plenums and concealed spaces, or shall be otherwise listed for the location.
+
+```datasheet
+label: Insulation Material
+type: radio
+options:
+ - "Closed-cell flexible elastomeric, ASTM C534 (standard)"
+ - "Closed-cell elastomeric with factory-applied protective jacket (exposed/exterior)"
+default: "Closed-cell flexible elastomeric, ASTM C534 (standard)"
+```
+
+```datasheet
+label: Suction Line Insulation Wall Thickness
+type: select
+unit: in.
+options:
+ - "1/2 in. — conditioned interior, short runs"
+ - "3/4 in. — standard interior, most commercial applications"
+ - "1 in. — long runs, high-humidity spaces, or where required by energy code"
+default: "3/4 in. — standard interior, most commercial applications"
+```
+
+```datasheet
+label: Liquid Line Insulation
+type: radio
+options:
+ - "Insulate suction line only; liquid line uninsulated (standard)"
+ - "Insulate both suction and liquid lines (heat-pump, long runs, or exposed liquid line)"
+default: "Insulate suction line only; liquid line uninsulated (standard)"
+```
+
+The suction line is always insulated to prevent condensation and to limit the heat gain that reduces capacity. The liquid line is normally left uninsulated because subcooling loss is small, but on heat-pump systems the "liquid" line carries warm vapor in heating mode and is insulated, and any liquid line exposed to high ambient or routed where its surface could sweat (or where it is subject to mechanical damage) shall be insulated. Insulation seams and butt joints shall be adhered with the manufacturer's contact adhesive to maintain the vapor seal; insulation shall not be stretched at fittings, as stretched elastomeric insulation thins and eventually pulls apart, breaking the vapor seal.
+
+# Pipe Sizing and Routing
+
+## Line Sizing
+
+Refrigerant line sizes shall be [[drawing: as indicated on the refrigerant piping drawings]] and shall conform to the equipment manufacturer's published line-size tables for the actual equivalent length and the lift between units. The Contractor shall not substitute line sizes. Both undersizing and oversizing cause problems: an undersized line raises pressure drop, lowers capacity, and increases compressor work; an oversized suction or discharge line reduces vapor velocity below what is needed to carry oil up vertical risers, so oil collects in the system and starves the compressor. Suction and discharge risers in particular shall be sized to maintain the minimum oil-entrainment velocity at the system's minimum-capacity (part-load) operating condition.
+
+```datasheet
+label: Line Sizing Basis
+type: radio
+options:
+ - "Per equipment manufacturer's line-size tables for actual equivalent length and lift (standard)"
+ - "Per Engineer's refrigerant piping design indicated on the drawings"
+default: "Per equipment manufacturer's line-size tables for actual equivalent length and lift (standard)"
+```
+
+## Maximum Length and Lift
+
+Total piping length, equivalent length, and the maximum vertical separation (lift) between the outdoor unit and the farthest or highest indoor unit, and between indoor units, shall not exceed the equipment manufacturer's published limits for the system and refrigerant. These limits are absolute; exceeding them voids the equipment warranty and causes loss of capacity, poor oil return, and migration problems. Where the layout cannot meet the limits, the Contractor shall notify the Engineer before installation rather than installing piping that exceeds them.
+
+```datasheet
+label: Maximum Total Refrigerant Pipe Length
+type: range
+unit: ft
+drawing_ref: true
+options:
+ min: 50
+ max: 3300
+ setpoints: [50, 100, 165, 300, 500, 1000, 1640, 3300]
+default: 165
+```
+
+```datasheet
+label: Maximum Vertical Separation (Lift) Between Outdoor and Indoor Units
+type: range
+unit: ft
+drawing_ref: true
+options:
+ min: 25
+ max: 360
+ setpoints: [25, 50, 90, 130, 165, 230, 360]
+default: 90
+```
+
+## Oil Return and Traps
+
+The piping shall be routed and trapped so that compressor lubricating oil returns reliably to the compressor under all operating conditions. On suction and discharge risers, oil P-traps (inverted traps at the top and a trap at the base of long risers) shall be provided where required by the equipment manufacturer's piping guidelines, typically at the base of each riser and at intervals up tall risers, to collect and lift oil in slugs at low load. Horizontal suction lines shall be pitched downward in the direction of flow toward the compressor to assist oil return. Double risers shall be provided where the manufacturer requires them to maintain oil-carrying velocity across a wide capacity-modulation range.
+
+```datasheet
+label: Oil-Return Provisions
+type: checkbox
+options:
+ - "Trap at base of each suction/discharge riser"
+ - "Intermediate traps on tall risers per manufacturer interval"
+ - "Inverted trap at top of riser to prevent drain-back"
+ - "Horizontal suction lines pitched toward compressor"
+ - "Double riser where required for part-load oil entrainment"
+default: "Trap at base of each suction/discharge riser"
+```
+
+## Routing and Branch Connections
+
+Branch connections, headers, and refnet/joint fittings on VRF systems shall be the equipment manufacturer's specified branch components and shall be installed in the orientation the manufacturer requires (typically horizontal or with the branches in the same horizontal plane) so that refrigerant and oil distribute correctly. Branch fittings shall not be installed in a vertical orientation unless the manufacturer expressly permits it. A minimum straight-pipe length shall be maintained before and after each branch as the manufacturer requires.
+
+# Refrigerant Safety (A2L, RCL, ASHRAE 15)
+
+## Refrigerant Quantity and Concentration Limits
+
+Where refrigerant piping passes through or serves an occupied space, the system refrigerant charge shall be limited so that, in the event of a full release into the smallest occupied space served by the system, the resulting concentration does not exceed the refrigerant concentration limit (RCL) for an A1 refrigerant, and for an A2L refrigerant does not exceed 25% of the lower flammability limit (LFL), in accordance with ASHRAE 15 and ASHRAE 15.2. The Contractor shall confirm that the as-installed charge (factory charge plus the line-length charge addition for the field piping) is within these limits for the smallest space served. Where the charge would exceed the limit, mitigation (a refrigerant detection system with ventilation or circulation) is required, or the system shall be reconfigured.
+
+```datasheet
+label: Refrigerant Concentration Compliance Basis
+type: radio
+options:
+ - "Charge limited so full release stays below RCL / 25% LFL in smallest occupied space (no mitigation)"
+ - "Charge exceeds limit — refrigerant detection system with mitigation provided per ASHRAE 15.2"
+default: "Charge limited so full release stays below RCL / 25% LFL in smallest occupied space (no mitigation)"
+```
+
+## Refrigerant Detection and Mitigation (A2L)
+
+For A2L systems where the charge or the served space requires it, a refrigerant detection system (RDS) listed to UL 60335-2-40 shall be provided. The detection sensor shall be located low in the space (A2L refrigerants are heavier than air and collect near the floor) at the location the equipment manufacturer specifies, and shall be set to alarm at a concentration below 25% of the LFL. On alarm, the system shall initiate the mitigation action specified by the manufacturer — typically energizing the indoor unit fan or a dedicated ventilation fan to disperse the refrigerant, and/or closing line-set isolation valves to limit the released quantity. Detection, alarm, and interlock wiring shall comply with NFPA 70. Sensors have a finite service life and shall be installed with the manufacturer's end-of-life replacement date recorded in the closeout documents.
+
+```datasheet
+label: A2L Mitigation Provisions (where required)
+type: checkbox
+options:
+ - "Refrigerant detection sensor(s) listed to UL 60335-2-40, located low in space"
+ - "Alarm interlock to indoor unit / circulation fan"
+ - "Dedicated mechanical ventilation interlock"
+ - "Automatic line-set isolation (shutoff) valves to limit released charge"
+ - "Audible/visual occupant alarm"
+default: "Refrigerant detection sensor(s) listed to UL 60335-2-40, located low in space"
+```
+
+## Piping in Occupied and Concealed Spaces
+
+Refrigerant piping installed in or through occupied spaces, plenums, shafts, and concealed locations shall be installed and protected so that a release is detected and mitigated as required above, and so that the piping is protected from mechanical damage. Joints in concealed and inaccessible spaces shall be minimized; where unavoidable, they shall be brazed (not mechanical or flare joints) to the maximum extent practicable, since brazed joints are the most leak-resistant. Tools used on A2L systems (recovery machines, vacuum pumps, gauges) shall be rated for the flammable refrigerant.
+
+# Joining and Brazing
+
+## Dry-Nitrogen Purge During Brazing
+
+While any joint is being brazed, the interior of the tube shall be continuously purged with a low, positive flow of oil-free dry nitrogen, and the purge shall be maintained until the joint has cooled. This is the single most important requirement of refrigerant brazing. Without an inert purge, the copper interior oxidizes in the brazing heat and forms a black, flaky cupric/cuprous oxide scale (firescale) inside the tube. That scale later breaks loose in the refrigerant and oil stream and travels to the metering device and compressor, plugging the expansion valve or capillary, scoring the compressor, and contaminating the oil. A clean nitrogen-purged braze leaves the bore bright; an unpurged braze permanently contaminates the system. Dry nitrogen is used as the purge gas — never oxygen, CO2, or shop air.
+
+```datasheet
+label: Dry-Nitrogen Purge During Brazing
+type: radio
+options:
+ - "Required on all brazed refrigerant joints, maintained until joint cools (standard)"
+default: "Required on all brazed refrigerant joints, maintained until joint cools (standard)"
+```
+
+## Brazing Procedure
+
+Tube ends shall be cut square with a tube cutter, reamed to remove the inside burr, and cleaned. The fitting and tube shall be assembled to the correct insertion depth. The joint shall be heated uniformly to brazing temperature and the filler metal applied so that capillary action draws filler completely into and around the socket, producing a continuous fillet. The tube shall not be overheated; localized overheating erodes the base metal and burns the surrounding insulation. Burrs, filings, and cut chips shall be kept out of the bore. A flow of nitrogen shall be passing through the tube during the entire heating and cooling of each joint.
+
+# Insulation
+
+## Application
+
+Insulation shall be applied after the piping has passed the pressure test and the leak test, but the Contractor shall plan the work so that joints to be insulated remain accessible for the test. Wherever practicable, elastomeric tube insulation shall be slipped over the tube before brazing the last joint (slid back during brazing, then returned and the seam sealed), rather than slit and re-sealed, because an unslit sleeve has no longitudinal seam to fail. Where insulation must be slit to install it, the seam and all butt joints shall be adhered continuously with the manufacturer's adhesive to restore the vapor seal.
+
+## Penetrations and Terminations
+
+Insulation shall be continuous through sleeves and penetrations and shall be protected where it passes through walls and floors. At terminations and at exposed exterior locations, the insulation shall be protected with a UV-resistant jacket or coating, because elastomeric insulation degrades under sunlight. Insulation shall not be compressed at pipe supports; insulation protection shields or inserts shall be used so the support load does not crush the insulation and create a condensation point.
+
+# Penetrations, Firestopping, and Support
+
+## Sleeves
+
+Refrigerant piping passing through walls, floors, and roofs shall be installed in sleeves sized to pass the insulated tube without compressing the insulation. Sleeves through fire-rated and floor assemblies shall extend as required by code, and the annular space shall be sealed.
+
+## Firestopping
+
+Penetrations of fire-rated walls, floors, and ceilings by refrigerant piping shall be sealed with a firestop system tested and listed for the penetrant (insulated copper tube) and the rating of the assembly, in accordance with [[sync/firestopping]]. The firestop system shall accommodate the combustible elastomeric insulation, which typically requires an intumescent device or wrap sized for the insulated tube.
+
+## Supports
+
+Piping shall be supported in accordance with MSS SP-58 at intervals appropriate to the tube size and temper, with closer spacing for soft-temper tube, and at every change of direction and at each piece of in-line specialty. Supports on insulated lines shall bear on a protection shield or insert so the insulation and its vapor seal are not crushed. Tube shall be isolated from dissimilar metal supports to prevent galvanic action and from sources of vibration; the connection to vibrating equipment shall include the manufacturer's vibration provisions so that vibration is not transmitted into brazed joints.
+
+```datasheet
+label: Maximum Support Spacing — Hard-Drawn Copper Tube
+type: select
+unit: ft (by tube OD)
+drawing_ref: true
+options:
+ - "Up to 5/8 in. OD — 6 ft; 3/4 in. to 1-1/8 in. OD — 8 ft; 1-3/8 in. OD and larger — 10 ft"
+ - "Per MSS SP-58 with closer spacing where indicated on drawings"
+default: "Up to 5/8 in. OD — 6 ft; 3/4 in. to 1-1/8 in. OD — 8 ft; 1-3/8 in. OD and larger — 10 ft"
+```
+
+# Pressure Testing, Evacuation, and Charging
+
+## Pressure and Leak Test
+
+After brazing is complete and before evacuation, the system field piping shall be pressure-tested with oil-free dry nitrogen (a small trace of refrigerant may be added to permit electronic leak detection, but the test medium shall be predominantly nitrogen — the system shall never be pressure-tested or "blown out" with oxygen or air). The high side and low side shall be tested to the test pressure required by ASME B31.5 and the equipment manufacturer, but not exceeding the lowest-rated component in the circuit. The pressure shall be held for the specified duration; the observed pressure shall be corrected for ambient temperature change before judging the result, because a 1°F change in nitrogen temperature shifts the gauge reading independently of any leak. A pressure drop not attributable to temperature indicates a leak, which shall be located and repaired and the joint re-tested.
+
+```datasheet
+label: Pressure Test Medium
+type: radio
+options:
+ - "Oil-free dry nitrogen (standard)"
+ - "Dry nitrogen with trace refrigerant for electronic leak detection"
+default: "Oil-free dry nitrogen (standard)"
+```
+
+```datasheet
+label: Pressure Test Hold Duration
+type: range
+unit: hours
+options:
+ min: 1
+ max: 24
+ setpoints: [1, 2, 4, 8, 12, 24]
+default: 4
+```
+
+## Evacuation
+
+After the system passes the pressure test, the nitrogen shall be recovered and the system evacuated with a vacuum pump to remove all air, non-condensable gas, and moisture. Evacuation shall be performed through both the high-side and low-side service ports using large-bore hoses or a core-removal tool so the pump can pull the system down efficiently. The system shall be evacuated to a final absolute pressure of 500 microns or lower. A triple (deep) evacuation shall be performed: evacuate, break the vacuum with dry nitrogen, evacuate again, break again, and evacuate a third time to the final 500-micron target. Breaking the vacuum with dry nitrogen between pulldowns dilutes and sweeps out residual moisture far more effectively than a single long pulldown, because water vaporizes slowly at low absolute pressure.
+
+```datasheet
+label: Evacuation Target (Final Absolute Pressure)
+type: range
+unit: microns
+options:
+ min: 250
+ max: 1000
+ setpoints: [250, 300, 500, 750, 1000]
+default: 500
+```
+
+```datasheet
+label: Evacuation Method
+type: radio
+options:
+ - "Triple evacuation with dry-nitrogen sweep between pulldowns (standard)"
+ - "Single deep evacuation to target with extended hold"
+default: "Triple evacuation with dry-nitrogen sweep between pulldowns (standard)"
+```
+
+## Decay (Standing Vacuum) Test
+
+After reaching the 500-micron target, the system shall be isolated from the vacuum pump (valve off the pump, leaving the micron gauge reading the system) and held. A system that is dry and leak-free will hold a steady vacuum or rise only slightly and stabilize. A rise that continues without stabilizing indicates a leak; a rise that stabilizes at a higher value indicates remaining moisture (off-gassing). The system shall pass a decay test before refrigerant is charged.
+
+```datasheet
+label: Standing-Vacuum Decay Acceptance
+type: radio
+options:
+ - "Hold isolated for 15 minutes; rise to no more than 500 microns and stabilizing (standard)"
+ - "Hold isolated for 30 minutes; rise to no more than 500 microns and stabilizing"
+default: "Hold isolated for 15 minutes; rise to no more than 500 microns and stabilizing"
+```
+
+## Charging
+
+Only the refrigerant specified for the equipment shall be charged; refrigerants shall not be mixed or topped off with a different refrigerant. Blended (zeotropic) refrigerants such as R-454B shall be charged from the cylinder as liquid (cylinder inverted or with a dip tube) to preserve the blend composition, then metered into the system per the equipment instructions. The total charge shall equal the factory charge plus the line-length charge addition calculated from the liquid-line size and length per the manufacturer's table, weighed in with a charging scale and recorded. The Contractor shall not charge by pressure or by sight glass alone where the manufacturer specifies a weighed charge.
+
+```datasheet
+label: Charging Method
+type: radio
+options:
+ - "Weighed charge: factory charge plus calculated line-length addition (standard)"
+ - "Weighed-in base charge, final trim per manufacturer subcooling/superheat target"
+default: "Weighed charge: factory charge plus calculated line-length addition (standard)"
+```
+
+# Installation
+
+## General
+
+The Contractor shall install all refrigerant piping in accordance with this standard, the contract drawings, ASME B31.5, the applicable ASHRAE safety standard, and the equipment manufacturer's installation instructions. Where these conflict, the more stringent governs. Tube shall be kept capped and under positive nitrogen pressure until the moment of brazing, and open tube ends shall be re-capped whenever work stops.
+
+## Cleanliness
+
+The interior of the piping shall be kept clean, dry, and free of oxide, moisture, flux, and debris throughout installation. The combination of capped ACR tube, the dry-nitrogen braze purge, the pressure test, and the triple evacuation is the means by which interior cleanliness is achieved and verified; none of these steps may be skipped. A filter-drier shall be installed in the liquid line where the equipment manufacturer requires one, and its location shall remain accessible for future replacement.
+
+## Coordination
+
+Routing, sizes, lengths, lifts, oil-trap and branch locations, and penetration locations shall be coordinated with the structural, architectural, and other trades on the coordination drawings before rough-in, and with the equipment standards [[sync/variable-refrigerant-flow-systems]] and [[sync/split-system-air-conditioners]]. Insulation thicknesses and the firestop systems shall be coordinated with [[sync/building-thermal-insulation]] and [[sync/firestopping]]. Routing shall be coordinated against [[drawing: the reflected ceiling plan and mechanical coordination drawings]].
+
+# Warranty
+
+The Contractor shall warrant the refrigerant piping installation against leaks and defects in materials and workmanship for a period of not less than one year from substantial completion, or for the period stated in the contract documents if longer. Any leak attributable to a field joint, and any compressor or metering-device failure attributable to interior contamination, inadequate evacuation, or moisture in the field piping, shall be corrected at the Contractor's expense, including the cost of recovering and recharging refrigerant and of replacing any contaminated refrigerant or oil. The installation shall not void the equipment manufacturer's warranty; the Contractor shall observe all manufacturer requirements (line sizing, length and lift limits, evacuation, and charge) on which that warranty depends.