1 Scope
NOTE This standard governs field-installed, replacement, and independently procured forced-circulation air-cooling and air-heating coils for HVAC systems in commercial, institutional, and industrial buildings. (1.1)
NOTE A forced-circulation coil is a finned-tube heat exchanger across which a fan moves air to add or remove sensible heat, and on cooling coils latent heat, by exchanging energy with a fluid circulating through the tubes — chilled water, hot water, steam, refrigerant, or glycol. (1.2)
NOTE The coil types covered are hydronic chilled water (CHW) cooling coils, hydronic hot water (HHW) heating coils, standard and distributing (non-freeze) steam heating coils, direct-expansion (DX) refrigerant coils, and glycol runaround heat-recovery coils. (1.3)
NOTE Both original-equipment coils ordered with an air handler and replacement or retrofit coils fabricated to fit an existing casing or field-built coil section are within scope. (1.4)
NOTE This standard covers coil construction, factory performance rating and certification, factory pressure testing, drain pan sizing and material, face velocity limits, installation clearances for coil removal, piping connection orientation, and commissioning verification. (1.5)
NOTE The following scopes are excluded from this standard: (1.6)
- Factory-assembled air handler integral coils where coil selection is delegated to the unit manufacturer — see Air Handling Units.
- Hydronic supply and return piping from the coil headers to the central plant (isolation valves, control valves, balancing valves, fittings, pipe insulation) — see Hydronic Piping, Control Valves And Actuators, and Mechanical Insulation.
- Steam supply and condensate return piping downstream of the coil steam trap — see Steam And Condensate Piping.
- Refrigerant piping connecting DX coils to condensing units (line sizing, leak testing, evacuation, brazing qualifications) — see Refrigerant Piping.
- Hydronic system flushing and chemical cleaning of connected piping and coils after installation — see Hydronic Cleaning And Flushing and Hvac Water Treatment.
- VRF indoor units with integral DX coils (factory-matched proprietary assemblies specified under the VRF system standard).
- Fin-tube radiation, baseboard convectors, and panel radiators (terminal heating devices without forced airflow; not forced-circulation coils under AHRI 410).
- Heat-exchanger coils in domestic hot water systems (plumbing heat exchangers, not HVAC air-side coils).
2 Referenced Standards
2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard |
Title |
| AHRI 410-2023 |
Performance Rating of Forced-Circulation Air-Cooling and Air-Heating Coils |
| ANSI/ASHRAE/IES 90.1-2022 |
Energy Standard for Buildings Except Low-Rise Residential Buildings |
| ASTM B75/B75M |
Seamless Copper Tube |
| ASTM B251 |
General Requirements for Wrought Seamless Copper and Copper-Alloy Tube |
| ASTM B359/B359M |
Copper and Copper-Alloy Seamless Condenser and Heat Exchanger Tubes With Integral Fins |
| ASTM A653/A653M |
Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process |
| ASME B31.9 |
Building Services Piping |
| NFPA 90A |
Standard for the Installation of Air-Conditioning and Ventilating Systems |
| IMC |
International Mechanical Code (current adopted edition) |
| ASHRAE Handbook |
HVAC Systems and Equipment (Air-Cooling and Dehumidifying Coils chapter) |
3 Submittals
3.1 Action Submittals
3.1.1The Contractor shall submit the following action submittals for review before fabrication or procurement:
- Product data for each coil type, including tube and fin material, tube OD and wall, fin density, number of rows, circuiting, casing material, and connection sizes and locations.
- AHRI 410 certified performance ratings for each coil, listing capacity, entering and leaving air and fluid conditions, airside and waterside pressure drop, and face velocity at design airflow.
- Coil selection calculations or manufacturer selection output showing capacity at the scheduled design conditions, including fouled-coil airside pressure drop allowance.
- Shop drawings showing coil face dimensions, tube depth, header and connection orientation, drain pan extent, and required pull-out clearance.
- Drain pan details for cooling coils, including material, slope, downstream extension, and trap seal depth.
- For DX coils, distributor type, number of refrigerant circuits, expansion device, and the matched condensing unit reference.
☑ Product data (materials, rows, fins, circuiting, connections)
☑ AHRI 410 certified performance ratings
☑ Coil selection calculations at design conditions
☑ Shop drawings (face dims, tube depth, connections, pull-out clearance)
☑ Drain pan details (material, slope, extension, trap seal)
☐ DX distributor, circuiting, and matched condensing unit data
3.2.1The Contractor shall submit the following informational submittals:
- Factory pressure test certificate for each coil, stating the test medium, test pressure, and duration.
- Manufacturer's AHRI ACHC certification confirming participation in the certification program for the rated coil line.
- Coating system data sheet and warranty for coated-fin coils, where coated fins are specified.
☑ Factory pressure test certificate
☑ AHRI ACHC certification confirmation
☐ Coating system data sheet and warranty (coated-fin coils)
3.3 Closeout Submittals
3.3.1The Contractor shall submit the following closeout submittals:
- Operation and maintenance data, including cleaning procedures, recommended face velocity for cleaning access, and coil-pull instructions.
- Record drawings showing as-installed coil locations, connection orientation, and condensate routing.
- Commissioning verification records, including measured airside and waterside pressure drop and leaving-air conditions.
☑ Operation and maintenance data
☑ Record drawings (locations, connections, condensate)
☑ Commissioning verification records
4 Quality Assurance
NOTE Each coil shall be rated and certified in accordance with AHRI 410. (4.1)
NOTE AHRI 410 is the primary performance rating standard for forced-circulation air-cooling and air-heating coils; it governs published capacity, airside and waterside pressure drop, and the AHRI ACHC (Air-Cooling and Air-Heating Coils) certification program under which an independent third-party laboratory verifies the manufacturer's rated capacities. (4.1.1)
4.1.2Coils shall carry AHRI 410 certified ratings for the scheduled capacity, pressure drop, and face velocity.
4.1.3The manufacturer shall participate in the AHRI ACHC certification program for the coil line supplied.
NOTE Certified ratings are mandatory for the energy code compliance documentation required under ASHRAE 90.1. (4.1.4)
NOTE A "minimum 200 psig" working-pressure callout without a certified rating leaves the engineer with no third-party verified capacity data and no basis for energy code compliance; certification is not optional. (4.2)
4.3Coil construction pressure ratings shall be consistent with the maximum allowable working pressure permitted by ASME B31.9 for the connected hydronic piping system.
4.4The manufacturer shall be regularly engaged in the production of forced-circulation HVAC coils and shall fabricate replacement coils to match the existing casing face dimensions, tube depth, and connection arrangement where retrofit coils are specified.
5 Environmental and Service Conditions
NOTE Coil material selection is driven by the corrosivity of the airstream and the fluid; standard copper-tube aluminum-fin construction is suitable for clean conditioned indoor air, while coastal, marine, and chemically aggressive airstreams require coated fins, all-copper, or stainless-tube construction. (5.1)
NOTE Standard aluminum fins corrode within roughly three to five years in salt-air or industrial airstreams, raising airside pressure drop and reducing capacity; the near-ocean threshold for upgraded fin protection is approximately three miles from saltwater. (5.2)
5.3Coated fins, all-copper construction, or stainless-steel tubes shall be specified where the coil serves a coastal, marine, or chemically corrosive airstream.
NOTE Galvanized-steel drain pans shall not be used below cooling coils; condensate at a typical pH of 5 to 7 attacks the zinc coating within a few years of service. (5.4)
5.5Drain pans below cooling coils shall be Type 304 stainless steel as a minimum, and Type 316 stainless steel in coastal or chemically aggressive environments.
● Clean conditioned indoor air (standard)
○ Coastal / marine (within ~3 miles of saltwater)
○ Industrial / chemically aggressive (chlorine, acidic gases)
● Bare aluminum fin (standard)
○ Phenolic or epoxy dip coating
○ Electrostatic-applied (e-coat) corrosion coating
○ All-copper fin
NOTE The coil type shall be selected to match the system fluid and service: chilled water, hot water, standard or distributing steam, direct expansion, or glycol runaround. (6.1)
● Chilled water (hydronic CHW cooling)
○ Hot water (hydronic HHW heating)
○ Steam, distributing / non-freeze
○ Steam, standard (non-distributing)
○ Direct expansion (DX refrigerant)
○ Glycol runaround (heat recovery)
6.2 Face Velocity
NOTE Face velocity is the air volume divided by the coil's net face area; it sets the airside pressure drop, the heat-transfer coefficient, and — on a wet cooling coil — whether condensate is blown off the fins and carried downstream. (6.2.1)
NOTE Cooling-coil face velocity above approximately 500 FPM begins to entrain condensate; 550 FPM is the absolute engineering maximum before moisture carryover off the fin surface becomes unavoidable. (6.2.2)
NOTE A specification that sets 500 FPM as the "maximum" and then permits a 10 percent selection margin unknowingly allows carryover; the carryover limit is a hard ceiling, not a target with headroom. (6.2.3)
6.2.4Cooling-coil face velocity shall not exceed 550 FPM at design airflow.
6.2.5Heating-only coils, which carry no condensate, may be selected at face velocities up to 700 FPM.
6.3 Rows and Fin Density
NOTE The number of tube rows and the fin density together set the coil's heat-transfer surface area; more rows and higher fin density raise capacity but also raise airside pressure drop and, on cooling coils, the risk of condensate bridging between fins. (6.3.1)
6.3.2Cooling coils shall be selected with the number of rows required to meet the scheduled capacity, typically four to eight rows.
6.3.3Heating coils shall be selected with the number of rows required to meet the scheduled capacity, typically one to four rows.
6.3.4Fin density shall be selected so the airside pressure drop, accounting for the fouled condition, remains within the design fan capability.
6.4 Circuiting
NOTE Circuiting is the routing of the fluid through the tube bundle — full-circuit, half-circuit, double-circuit, or face-split — and it sets the waterside velocity, waterside pressure drop, and part-load behavior. (6.4.1)
NOTE Half-circuit configurations raise tube velocity and waterside pressure drop but improve heat transfer and stability at low loads, which is why high-turndown chilled water coils are often half-circuited. (6.4.2)
6.4.3Coil circuiting shall be selected to keep waterside velocity within the tube manufacturer's erosion limit while meeting the scheduled waterside pressure drop.
○ Full circuit
● Half circuit
○ Double circuit
○ Face split
6.5 Fluid Conditions
6.5.1Chilled water coils shall be selected for the scheduled entering and leaving water temperatures, with a default design of 44 °F entering and 56 °F leaving.
6.5.2The chilled water temperature differential shall be not less than 15 °F where required by ASHRAE 90.1 Section 6.5.4 for the system capacity in question.
NOTE ASHRAE 90.1 Section 6.5.4.5 requires a minimum 15 °F chilled water temperature differential across cooling coils above a threshold system capacity; coordinate the design delta-T with the mechanical engineer of record. (6.5.3)
6.5.4Hot water coils shall be selected for the scheduled entering and leaving water temperatures, with a default design of 180 °F entering and 160 °F leaving.
6.5.5Entering and leaving air conditions, expressed as dry-bulb and wet-bulb for cooling coils and dry-bulb only for heating coils, shall be scheduled and shall match the coil selection basis.
6.6 Counterflow Arrangement
NOTE In a counterflow arrangement the water supply enters at the leaving-air end of the coil and exits at the entering-air end, which maximizes the log-mean temperature difference across the bundle. (6.6.1)
NOTE A parallel-flow circuit — water supply entering the same end as the entering air — reduces the effective LMTD by 15 to 25 percent relative to counterflow, yet coil submittals often default to whichever connection is mechanically convenient unless counterflow is explicitly required. (6.6.2)
6.6.3Chilled water and hot water coils shall be piped for counterflow, with the water supply connected at the leaving-air end of the coil.
● Counterflow (supply at leaving-air end)
○ Parallel flow (supply at entering-air end)
7 Coil Construction
7.1 Tubes
7.1.1Coil tubes shall be seamless copper conforming to ASTM B75/B75M and the general requirements of ASTM B251, unless stainless steel tubes are specified for a chemically aggressive airstream.
NOTE Integral-fin (enhanced surface) copper tubes, where used, shall conform to ASTM B359/B359M. (7.1.2)
7.1.3The standard commercial coil tube shall be 5/8 in. OD copper with a 0.020 in. nominal wall; 1/2 in. and 1 in. OD tubes are available where the selection requires them.
● Copper (seamless, ASTM B75)
○ Stainless steel (chemically aggressive airstream)
7.2 Fins
7.2.1Fins shall be continuous plate fins mechanically bonded to the tubes by mechanical expansion of the tube into the fin collar.
7.2.2Fin material shall be aluminum for standard service, copper for coastal service, or factory-coated aluminum for marine and chemically aggressive service, consistent with the airstream corrosivity classification.
● Aluminum (standard)
○ Copper (coastal / corrosive)
○ Coated aluminum (marine / chemical)
7.3 Casing and Frame
7.3.1The coil casing and frame shall be galvanized steel conforming to ASTM A653/A653M, stainless steel, or aluminum as scheduled.
NOTE Casing materials, coatings, and drain pans located in the airstream shall meet the flame-spread and smoke-developed limits of NFPA 90A. (7.3.2)
● Galvanized steel (ASTM A653)
○ Stainless steel
○ Aluminum
7.4 Headers and Connections
7.4.1Headers and connections shall be sized for the scheduled flow and shall be located on the side and end shown so the coil mates to the connected piping without field rework.
NOTE Connection orientation — same-end versus opposite-end, and connection side — shall be coordinated with the piping layout and, for replacement coils, shall match the existing piping. (7.4.2)
7.4.3Coil design working pressure shall be not less than 200 psig at 325 °F for standard commercial hydronic coils.
● Same end (supply and return)
○ Opposite ends
8 Steam Coils
NOTE A standard (non-distributing) steam coil is single-tube construction in which condensate drains along the bottom of each tube; a distributing (non-freeze) coil places an inner perforated tube within the outer tube so live steam reaches the full length of every tube regardless of the condensate level. (8.1)
8.2Standard (non-distributing) steam coils shall be used only in indoor steam applications where the entering air is always above freezing and condensate cannot accumulate against sub-freezing air.
NOTE Specifying a standard steam coil where outdoor air below 32 °F can reach the coil face is a freeze failure: condensate pools in the bottom tubes, freezes, and bursts the tubes. (8.3)
8.4Distributing (non-freeze) steam coils shall be specified for every mixed-air, outdoor-air, or preheat application where air below 32 °F can reach the coil face.
NOTE Each distributing-coil circuit shall discharge through a float-and-thermostatic steam trap sized for the supply pressure plus a safety factor. (8.5)
8.6Steam supply pressure for distributing heating coils shall be as scheduled, typically in the range of 2 to 15 psig.
● Distributing / non-freeze (inner-tube)
○ Standard / non-distributing (indoor, non-freezing only)
9 Direct-Expansion Coils
NOTE A DX coil is a refrigerant evaporator: liquid refrigerant is metered through a distributor and expansion device into multiple parallel circuits, evaporates as it absorbs heat from the air, and leaves through a suction header to the matched condensing unit. (9.1)
9.2DX coil distributor type, number of refrigerant circuits, and expansion device shall be matched to the specific condensing unit refrigerant, capacity, and expansion control.
NOTE A DX coil whose circuiting does not match the condensing unit causes oil logging, flash gas in the distributor, and capacity loss; the coil and condensing unit are a matched pair, not independently selected components. (9.3)
NOTE Refrigerant piping between the DX coil and the condensing unit, including line sizing, leak testing, evacuation, and brazing qualifications, is specified under
Refrigerant Piping.
(9.4) ● Thermostatic expansion valve (TXV)
○ Electronic expansion valve (EXV)
10 Glycol Runaround Coils
NOTE A glycol runaround loop pairs a coil in the supply airstream with a coil in the exhaust airstream, connected by a pumped glycol circuit, to recover energy between physically separated supply and exhaust air handlers. (10.1)
NOTE Glycol runaround coils shall be constructed as hot water coils but selected and rated for the design glycol concentration and the resulting fluid properties. (10.2)
NOTE The pumped glycol piping loop connecting the paired coils is specified under
Hydronic Piping, while this standard governs the runaround coil construction and rating.
(10.3) 11 Drain Pans
NOTE A drain pan under a cooling coil must capture all condensate that drips from the fin surface and all condensate that is blown off the leaving face and entrained downstream; an undersized pan lets condensate reach the fan section and downstream duct, where it promotes biological growth and corrosion. (11.1)
11.2Drain pans shall be provided below all cooling coils and below any coil where condensation can occur.
11.3The drain pan shall slope toward the drain connection at not less than 1/8 in. per ft, with 1/4 in. per ft preferred.
11.4The drain pan shall extend downstream of the coil leaving face by not less than 2 in. per foot of coil height, and in no case less than 6 in.
NOTE Omitting the downstream drain pan extension dimension from the drawings allows blown-off condensate to bypass the pan; the extension is a dimensioned requirement, not a default. (11.5)
● Type 304 stainless steel
○ Type 316 stainless steel (coastal / chemical)
0.1250.25
Default: 0.25 in/ft
11.6 Condensate Trap
11.6.1The condensate drain shall be trapped, and the trap seal depth shall equal the negative static pressure at the drain pan in inches w.g. plus a 2 in. minimum.
NOTE A trap sized for less than the actual negative static pressure at the drain section air-locks on a draw-through unit or blows through on a blow-through unit, causing pan overflow and sewer-gas ingestion; the seal depth is governed by the actual pan static pressure, not a fixed dimension. (11.6.2)
● Draw-through (negative pressure at pan)
○ Blow-through (positive pressure at pan)
12 Testing
12.1Standard hydronic coils shall be factory hydrostatically tested at 300 psig, which is not less than 1.5 times the maximum allowable working pressure, with the test pressure applied to the waterside and the airside vented.
12.2DX coils shall be factory leak-tested by pneumatic or helium leak test appropriate to the refrigerant service.
12.3A factory pressure-test certificate stating the test medium, test pressure, and duration shall be furnished for each coil.
12.4 Field Verification
12.4.1Installed coils shall be commissioned in coordination with Testing Adjusting And Balancing to confirm design airflow, airside and waterside pressure drop, and leaving-air conditions. NOTE Measured airside pressure drop shall be compared against the clean-coil rating, and the fan selection shall be confirmed to accommodate the fouled-coil allowance. (12.4.2)
☑ Design airflow at coil face confirmed
☑ Airside pressure drop measured vs. rating
☑ Waterside pressure drop / flow confirmed
☑ Leaving-air conditions verified at design load
☐ Control valve / BAS integration verified
13 Installation
13.1Coils shall be installed level and square in the casing or duct, with the fin face perpendicular to airflow and the tube headers oriented as scheduled.
NOTE A replacement coil must be removable from its casing without cutting the coil frame or disassembling adjacent ductwork; pull-out clearance that is not confirmed at design produces RFIs and change orders at the retrofit. (13.2)
13.3Pull-out clearance equal to the full coil width plus access shall be provided so the coil can be removed without cutting tube or disassembling adjacent sections.
13.4Pull-out clearance and access location shall be confirmed and shown on the drawings coil pull space. 13.5Replacement coils shall match the existing coil face height and width, tube depth (rows times row spacing), connection size, and connection location, verified by field measurement before fabrication.
NOTE A replacement coil selected to the existing face dimensions alone, without verifying tube depth and connection location, will not connect to the existing piping without rework. (13.6)
13.7Hydronic coils shall be piped with the supply and return connected for the scheduled counterflow arrangement.
13.8High-point vents and low-point drains shall be provided at each hydronic coil.
13.9Steam coil condensate connections shall be piped to the trap with the pitch and drip-leg arrangement required for the coil construction type, with connection to the condensate system per Steam And Condensate Piping. NOTE Coil headers and connection stubs shall be insulated under
Mechanical Insulation after pressure testing and acceptance.
(13.10) 13.11Coil installation shall comply with the drain pan, trap, and clearance provisions of the International Mechanical Code and the airstream material provisions of NFPA 90A.
NOTE General mechanical coordination, access, identification, and equipment support requirements common to this work are addressed under
Common Work Results Mechanical.
(13.12) NOTE Coils serving dedicated outdoor air units shall be coordinated with the deep-cooling and dehumidification provisions of
Dedicated Outdoor Air Systems.
(13.13) 14 Delivery, Storage, and Handling
14.1Coils shall be delivered with header connections capped and the tube bundle protected against handling damage to the fins.
14.2Coils shall be stored indoors or under cover, protected from weather, dust, and physical damage, and kept dry until installation.
14.3Coils shall be handled by the casing or designated lifting points, never by the headers or connections, to avoid distorting the tube bundle.
15 Warranty
15.1The manufacturer shall warrant each coil against defects in materials and workmanship for not less than 12 months from substantial completion or 18 months from shipment, whichever occurs first.
15.2Coated-fin coils shall carry the coating manufacturer's corrosion warranty for the scheduled coating system in addition to the coil warranty.
16 Spare Parts
16.1The Contractor shall furnish the spare parts and consumables required to maintain coil service, as scheduled.
☑ Spare condensate trap assembly (one per coil type)
☐ Spare distributing-steam-coil F&T trap (steam coils)
☐ Spare fin comb for fin straightening