Frequently asked questions
Custom coil and heat exchanger questions, answered.
79 questions collected from the product, application and technical guide pages. Each group links to the page where the topic is covered in full.
Product questions
Stainless helical coils
What is a stainless steel heat exchanger coil?
A stainless steel heat exchanger coil is most often a helical coil: a tube formed into a continuous spiral so that a heating or cooling medium can flow through it while the coil sits inside a tank, vessel or compact piece of equipment. The helical shape fits a long tube length into a small envelope and gives the surrounding medium a large contact surface. Uniinox supplies these coils to the customer's drawing. The supplied 2026 custom-coil catalog documents nine 304 stainless steel reference configurations, P01 to P09, with tube outside diameters of 9.52 mm, 12 mm and 22 mm, wall thicknesses of 0.7 mm to 1.0 mm and overall heights from 160 mm to 880 mm. Single-circuit, dual-circuit, top-connection, compact and tapered layouts are shown. These references are starting points for a drawing review: the final grade, dimensions, connection ends, tolerances and inspection scope are set by the approved project drawing.
Can a stainless steel helical coil be quoted from a drawing?
Submit the drawing with tube outside diameter, wall thickness, coil diameter, height and connection details. Identify the required material grade and quantity. Catalog configurations are references; the quotation must identify the agreed drawing and material.
Does the coil photograph establish its pressure rating?
No. A photograph shows the arrangement, not a pressure or temperature rating. Include the operating conditions and required inspection documents in the inquiry so the proposed construction can be reviewed.
Finned heat exchanger cores
What is a finned tube heat exchanger core?
A finned tube heat exchanger core is a bundle of tubes passed through a stack of thin metal fins, so that air flowing across the fins exchanges heat with the fluid or refrigerant inside the tubes. The fins multiply the air-side surface area, which is why finned cores are the basis of most HVAC coils: condensers, evaporators, air coolers and heating or cooling coils. Uniinox produces compact and large-format custom copper-tube finned cores, including coated coil assemblies. The published capability references are a fin thickness of 0.10 mm to 0.25 mm and a tube outside diameter of 6 mm to 32 mm. Fin material, fin spacing, coating, circuiting and performance are not assigned from a photograph. Each core is confirmed against the project drawing, the required duty and the operating data before production, so that the supplied core matches the equipment it is built for.
What should an inquiry for a finned heat exchanger include?
State whether you need a replacement core or a new design. Provide the available dimensions, tube and fin requirements, fluid, airflow, inlet and outlet conditions, connections and quantity. Attach an existing drawing or datasheet when available.
Is a finned core the same as a complete cooling unit?
No. A core does not by itself define fans, controls, enclosure or installation accessories. List the components you expect to be included so the quotation clearly separates the core from the complete assembly.
Copper tube fabrication
What is copper tube fabrication for heat exchangers?
Copper tube fabrication is the cutting, straightening, bending and end preparation of copper tube into parts that are later joined into heat exchangers, coils and refrigeration assemblies. Typical parts include straight tube sections, U-bends and return bends, formed connection tubes and small subassemblies. Uniinox works from drawing-based part definitions, processing straight lengths and coil-fed tube on forming equipment and preparing tube ends for assembly, as shown in the manufacturing gallery. The copper grade, outside diameter, wall thickness, bend radius, tolerances and joint method are order-specific and are confirmed before production. When the request covers a complete coil or finned core rather than loose parts, the copper tube coil or finned heat exchanger route is usually the better fit, because the review then covers the formed geometry and the connections as one unit. A dimensioned drawing with bend positions and end details is the fastest basis for a quotation.
What details are needed for custom copper tube fabrication?
Include tube outside diameter and wall thickness, bend radii, straight lengths, end preparation and dimensional tolerances. Mark the connection orientation on the drawing and specify the quantity and intended service.
Can a photo replace a copper tube fabrication drawing?
A photo is useful for identifying the shape but does not reliably show dimensions or tolerances. Supply measurements or a dimensioned drawing before confirming the manufacturing scope.
Integrated assemblies
What is a tank-integrated coil and header assembly?
A tank-integrated coil and header assembly is a coil, together with its headers and connection pieces, made to be installed as one unit inside a vessel or packaged unit rather than supplied as a loose tube. Combining the coil, the headers and the support or frame interfaces in one assembly means the connection layout, flow direction and fit inside the vessel are reviewed before production instead of on site. Uniinox coordinates the coil, header, frame and casing interfaces for these projects and supports finished-unit and shipment preparation. Supplied factory photography shows internal vessel coils, multi-connection headers and packaged air-cooled units. Product naming, capacity, flow direction and electrical data follow the approved drawing and nameplate. For complete OEM equipment with several fabricated components, the custom OEM heat exchanger assembly route covers the wider supply scope.
How should I define a heat-transfer assembly for quotation?
List each required component and its interface: coil or core, shell, supports, ports and mounting points. Identify which components are included in the supply and which will be provided by your installation team.
Does an assembly photo confirm that controls and testing are included?
No. Photos document a physical configuration, not the contractual supply or test scope. Specify controls, inspection records and acceptance requirements separately in the inquiry.
Immersion heating and cooling coils
What is an immersion coil heat exchanger?
An immersion coil heat exchanger, also called an immersion heating or cooling coil or an immersion tube coil, is a heat exchanger coil placed directly in the liquid it heats or cools, such as the contents of a tank, vat or process vessel. Hot water, steam, chilled water or another medium flows through the tube while the surrounding liquid takes up or gives off heat across the tube wall. The coil therefore has to fit the tank envelope, sit at the right position in the liquid and leave room for support, cleaning and removal. Uniinox forms immersion coils around the available tank envelope, the required connection direction and the approved tube route, using helical, compact and top-connection layouts. The supplied catalog provides 304 stainless steel reference geometries with tube outside diameters from 9.52 mm to 22 mm. The final material, dimensions, working medium, pressure, temperature and mounting details remain project-defined and are fixed in the approved drawing.
What information is needed for an immersion coil inquiry?
Provide the tank opening and internal dimensions, immersion depth, mounting arrangement, process liquid and coil-side fluid. Include temperatures, required duty and connection locations for a project-specific review.
Can I choose an immersion coil only by its outside dimensions?
Dimensions establish whether it fits, but not whether it is suitable for the process. Material compatibility, operating conditions and the required heating or cooling duty also need review.
Copper tube coils
What is a copper tube coil?
A copper tube coil is a length of copper tube bent into a helical or project-specific shape to carry a fluid or refrigerant for heating, cooling or heat recovery. Custom copper coils are formed to the buyer's dimensions and connection details rather than taken from stock lengths. Copper is chosen for its high thermal conductivity and good formability, although compatibility with the medium and the service conditions still has to be checked for each project. Uniinox produces helical and formed copper coils with straight sections, return bends and end preparation, and factory photography documents the copper tube stock, coil-fed processing and finished coil stages. Before a copper coil is released for production, the tube grade, outside diameter, wall thickness, bend radius, overall envelope and joint details are reviewed against the drawing. For stainless steel service, or where the medium is not compatible with copper, the stainless helical coil route is the closer comparison.
How do I request a replacement copper tube coil?
Send an existing drawing or measured sample details, including tube size, coil envelope, number of turns and inlet and outlet positions. State the application and quantity, and mark any dimensions that must match the existing installation.
Are all copper coils interchangeable if the tube size matches?
No. Coil geometry, connections, material specification and service conditions also matter. Confirm the complete drawing and application requirements before approving a replacement.
Industrial condensers
What is an industrial condenser coil?
An industrial condenser coil is a finned tube heat exchanger in which hot refrigerant vapour gives up heat to the air flowing across the fins and condenses to a liquid. It is the heat-rejection side of a refrigeration or heat pump cycle, so its size depends on the heat to be rejected, the refrigerant, the condensing temperature and the air conditions. Uniinox coordinates fin preparation, copper tube insertion, return bends, headers and final assembly for custom condenser projects in compact and large formats. Capacity is not assigned from a photograph or a catalog picture. Each quotation starts from the heat-rejection duty, refrigerant, condensing condition, airflow, entering air temperature, allowable pressure drop and installation envelope, so that competing offers for the same condenser can be compared on the same rating basis. The same inputs are listed in the Uniinox condenser and evaporator RFQ guide.
What should I send when requesting an industrial condenser?
Identify the working fluid and cooling medium, required duty, operating temperatures and pressures, available space and connection details. For replacement work, attach the existing datasheet and installation drawing.
Can a condenser be selected from its photo or overall size?
A photo or envelope dimension cannot establish capacity. The selection needs the stated operating conditions and heat-transfer requirements; the quotation should identify the conditions used for review.
Industrial evaporators
What is an industrial evaporator coil?
An industrial evaporator coil is a finned tube heat exchanger in which liquid refrigerant absorbs heat from the air or product being cooled and evaporates inside the tubes. It is the cooling side of a refrigeration cycle, used in cold rooms, process cooling and air-handling equipment. Because the coil may run below the dew point or below freezing, moisture removal, frost and defrost behaviour affect the design as much as the cooling duty does. Uniinox coordinates fin, tube, return bend and connection work for compact and project-specific evaporator cores. Each evaporator is reviewed against the required cooling duty, refrigerant, entering and leaving conditions, airflow, defrost or coating needs and installation space. The approved calculation basis and drawing then control the supplied configuration, rather than a photograph or a generic model number. The Uniinox condenser and evaporator RFQ guide lists the inputs to send.
Which information helps define an industrial evaporator inquiry?
Provide the working fluid, application, required duty, operating conditions, available dimensions and connection arrangement. Clarify whether the request covers a heat-exchanger component or additional equipment.
Can an evaporator replace a condenser with a similar appearance?
Do not assume interchangeability from appearance. Their intended service and operating conditions differ. Supply the original specification and have the replacement scope reviewed against the actual process.
Air cooler heat exchangers
What is an air cooler heat exchanger?
An air cooler heat exchanger is a finned core combined with a frame, casing and fan interface, so that air is moved across the fins to cool, or sometimes heat, the fluid or refrigerant inside the tubes. The core sets the heat-transfer surface, while the casing and fan arrangement decide how air reaches it and how the unit is installed. Uniinox coordinates the finned coil, headers, frame, casing and connection interfaces for drawing-based air cooler projects and prepares completed assemblies for shipment. Supplied photographs show packaged air-cooled units and their core components. Fan selection, electrical data, duty and the final product configuration follow the approved project specification. When only the finned core is required, the finned heat exchanger route covers the core without the casing and fan interfaces, which keeps the supply boundary clear.
What should an air-cooler heat exchanger inquiry specify?
Include the air-side and tube-side conditions, required duty, available dimensions, mounting points and connections. State whether fans, a housing or controls are required in addition to the heat-exchanger core.
Does a pictured fan opening mean fans are supplied?
Not necessarily. An opening or housing shown in a reference photo does not establish the bill of materials. Ask for a quotation that explicitly lists fans, motors, electrical requirements and any excluded items.
Custom OEM heat exchanger assemblies
What is a custom OEM heat exchanger assembly?
A custom OEM heat exchanger assembly is a heat-transfer component built to an equipment manufacturer's drawing set, in which coils, headers, frames, casings or vessel parts are made and coordinated as one supplied unit. Buying the assembly rather than separate parts moves interface, fit and inspection coordination to one supplier, provided the supply boundary is clearly defined. Uniinox supports drawing-based OEM projects that bring several fabricated components together into one assembly. The review covers interfaces, tube routes, headers, casing or vessel integration, inspection points, packing and release documentation, and no performance figure is assigned without a verified calculation basis. Supplied factory photography documents integrated vessel coils, headers, tank modules and packaged units. The order defines the inspection and packing scope before production release. A complete drawing set, a supply-boundary list and the required inspection documents are the best starting point for this type of enquiry.
How do I prepare an OEM heat exchanger assembly inquiry?
Send the assembly drawing, interface dimensions, component list, operating requirements and quantity. Identify critical tolerances, inspection requirements and the drawing revision that should be used for quotation.
Can a catalog example serve as an approved OEM specification?
A catalog example is a starting reference, not an approval document. Confirm the project drawing, materials, scope of supply and acceptance criteria before placing an order.
Application questions
HVAC air handling unit coils
What face velocity should an AHU cooling coil be designed for?
There is no single value. Many owner standards cap it to limit moisture carryover: NIH requires no more than 2.0 m/s (400 fpm) at present design conditions, and Michigan State University specifies a maximum of 500 fpm across the finned area for chilled-water and DX coils. Use the value in your project specification and include it in the RFQ.
How many fins per inch does an HVAC coil have?
It depends on the duty and the cleaning requirement. Some owners set limits: NIH allows at most 10 fins per inch on cooling coils, and MSU requires at least 0.125 in between fins, about 8 fins per inch. Fin pitch in millimetres is 25.4 divided by the fins per inch.
Can Uniinox build a replacement coil for an existing air handling unit?
Uniinox reviews replacement-core requests from the existing coil's measurements, drawing or datasheet. Send the finned dimensions, rows, fin spacing, tube size and connection details, together with the operating conditions so the duty can be checked rather than only copied.
Is an AHU coil the same as a complete air handling unit?
No. The coil is one component. Fans, filters, dampers, casing, controls and drain pan are separate items unless the RFQ lists them as part of the supply.
Refrigeration condenser and evaporator coils
Why do freezer evaporators have fewer fins per inch?
Frost builds on the fins and blocks the airflow. Wider spacing gives the frost somewhere to collect between defrosts. ACHR News gives about 4 fins per inch, and no more than 6, as typical for low-temperature evaporators, against 6 to 8 or more for medium- and high-temperature units.
Can a copper-tube coil be used with ammonia?
No. BITZER states that ammonia (R717) attacks copper materials and that lines and heat exchangers should be steel or stainless steel. Always state the refrigerant in a coil enquiry.
Which defrost method should I specify?
That is a system decision. Off-cycle defrost only works for rooms above 0 °C; electric and hot-gas defrost are used for lower temperatures. Because each method affects how the coil is built, state the chosen method in the enquiry.
Does Uniinox publish rated capacities for refrigeration coils?
No. Product pages do not publish ratings. Capacity is reviewed against your operating data for each project. If your project requires an AHRI-certified unit cooler, state that requirement in the RFQ.
Replacement HVAC and refrigeration coils
Can a coil be replaced using only the model number?
A model number can help identify the original design, but Uniinox builds to measured dimensions or a drawing. Send the measurements and photos as well, so the new coil can be checked against the space and connections.
How do I tell whether a coil is right-hand or left-hand?
One common method, used in Marlo's replacement guide, is to look at the coil in the direction of airflow and note which side the connections are on. Conventions differ between drawings, so mark the connection side on a photo of the coil.
How do I count fins per inch?
Count the fins over 3 or 4 inches and divide by that length. To convert to fin pitch in millimetres, divide 25.4 by the fins per inch.
Do I need the original coil's performance data?
It is strongly recommended. With the original datasheet or nameplate and the current operating conditions, the replacement can be checked against the duty instead of only matching the dimensions.
Coils for OEM equipment
Can Uniinox build to our existing drawing?
Yes. Uniinox works from the buyer's drawing or project requirements. Catalog configurations are references only; the approved drawing controls production.
Which inspection documents can be supplied?
The scope is agreed for each order. List the dimensional reports, pressure or leak test records and material documents you need in the enquiry; their availability is confirmed in the quotation.
What is needed to quote a repeat OEM part?
The current drawing revision, the material, the inspection and packing requirements, the annual quantity and the typical batch size.
Can several components be supplied as one assembly?
Yes. Uniinox coordinates coils, headers, frames, casings and vessel interfaces as one drawing-based assembly. Identify every interface and which parts your team will supply.
Technical guide questions
Heat Exchanger RFQ Checklist
Can I request a quotation without a finished drawing?
Yes. A dimensioned sketch and complete operating inputs can start the review, but final production remains controlled by an approved drawing.
Why is airflow needed for a finned heat exchanger?
Airflow and air conditions are part of the design basis for air-side heat transfer and pressure-drop review.
Does citing an AHRI or ASHRAE document make a custom exchanger certified?
No. A reference can explain terminology or the information used for selection. Certification or conformance should only be claimed for a product and scope supported by specific evidence.
What should I do when one RFQ input is not yet known?
Mark it as an open item, explain the expected range if one is known and ask what must be confirmed before selection or drawing approval. Do not present an assumed value as customer data.
Custom Coil Design Inputs
Can a catalog coil size be modified?
Yes. Catalog geometries are reference starting points; final dimensions and interfaces are reviewed against the project drawing.
What is the most important dimension for an immersion coil?
There is no single universal dimension. The complete installation envelope, access opening and connection position need to be reviewed together.
Can 304 stainless steel be assumed for every immersion coil?
No. Media composition, temperature, contaminants, cleaning method, fabrication and the project design basis all affect material review. State the requested grade, but provide the service information needed to verify it.
Why should cleaning chemicals be included in the enquiry?
Cleaning exposure can differ from normal operation and may affect material compatibility, surface requirements and whether the coil must be removable for maintenance.
Can a coil be made from a photo or an existing sample?
A photo helps identify the shape, but production needs dimensions. Measure the existing coil with the coil measurement worksheet or send a drawing, and mark which dimensions must match the installation.
Should the tube be welded or seamless?
ASTM A269 covers both seamless and welded austenitic stainless tubing. State which one your specification requires; if it does not say, include the service conditions so the choice can be reviewed.
What is the difference between a single-circuit and a dual-circuit coil?
A single-circuit coil has one continuous flow path. A dual-circuit coil splits the flow into two parallel paths, which shortens the path length per circuit within a similar overall size.
Condenser vs Evaporator: RFQ Information
Can a photograph confirm whether a coil is a condenser or evaporator?
Not reliably. The function and operating data must be confirmed before the product is classified for quotation.
Do condenser and evaporator quotations use the same inputs?
They share mechanical inputs, but the thermal and operating data differ because one rejects heat and the other absorbs heat.
Is condenser heat rejection the same as evaporator cooling capacity?
Not generally in a conventional vapor-compression system. The condenser rejects the heat absorbed in the evaporator plus energy added elsewhere in the cycle, including compression. Use the project calculation for the actual operating point.
Can matching dimensions prove that a replacement coil has matching capacity?
No. Dimensions establish fit, while capacity also depends on the fluids, temperatures, airflow or flow rate, circuiting, surface and operating conditions.
What is the difference between an evaporator coil and a condenser coil?
The evaporator coil absorbs heat from the space, air or liquid being cooled while the refrigerant inside evaporates. The condenser coil rejects that heat, plus the energy added by the compressor, while the refrigerant condenses back to a liquid.
Where is the evaporator coil located?
In the space or air stream being cooled: inside a cold room unit cooler, an air handler or a fan coil. The condenser coil sits where the heat can be rejected, such as outdoors, on a roof or in a machine room.
Tube Diameter and Wall Thickness for Custom Coils
Is tube OD the same as connection size?
Not necessarily. State both the actual tube dimensions and the required connection details.
Can I choose wall thickness from the website alone?
No. The final selection depends on material, pressure, temperature, medium, forming geometry and the approved design basis.
Is nominal connection size the same as tube outside diameter?
Not necessarily. State the tube OD and wall as actual dimensions, then define the connection and end preparation separately.
Can a catalog tube size be treated as a pressure rating?
No. A catalog dimension documents a reference geometry. Pressure and temperature suitability require the complete material, mechanical and project design basis.
Stainless Steel vs Copper Heat Exchanger Coils
Is a copper coil always more efficient than a stainless steel coil?
No. Copper has much higher thermal conductivity, but in many liquid services the fluid films and fouling limit heat transfer more than the tube wall. The difference has to be checked against the actual operating conditions.
Can copper coils be used with ammonia refrigerant?
No. Ammonia (R717) attacks copper materials, so ammonia systems use steel or stainless steel lines and heat exchangers.
Which material is usually chosen for food or beverage tanks?
Stainless steel is the usual starting point because of hygiene and cleaning requirements. The grade still depends on the product, cleaning chemicals and chloride exposure.
Should I specify 304 or 316L stainless steel?
It depends on the service. Chloride content, temperature and cleaning chemicals are the main factors. The Uniinox catalog reference coils are 304; send the media data so the grade can be reviewed for your project.
Tank Heating and Cooling Coils
Should I use a helical or a rectangular coil in my tank?
Use the shape that follows the tank: helical coils suit round tanks and vessels, rectangular coils suit rectangular tanks and baths. The access opening and internal fittings also affect the choice.
How do I know how much coil surface I need?
The surface area is calculated from the heat load, the temperature difference and the overall heat transfer coefficient, which depends strongly on the liquid and agitation. Send the duty and operating conditions so the area can be reviewed.
Can the coil be removed for cleaning?
Yes, if the coil and tank are designed for it. Side-hung coils and coils on a removable cover plate are common ways to allow removal; show the access opening on the drawing.
Can Uniinox supply the coil together with the vessel?
Coil-only supply is the usual starting point. Coils integrated with a vessel, headers or mounting plates can be reviewed as an OEM assembly enquiry.
Glycol in Heat Exchanger Coils
Is propylene glycol or ethylene glycol better for a cooling coil?
Ethylene glycol gives better heat transfer and lower viscosity. Propylene glycol has low oral toxicity and is the usual choice where food, beverage or drinking water could be contaminated. Choose the fluid for the safety requirement first, then size the coil for that fluid.
How much glycol does a coil loop need?
Enough to give a freezing point at least about 3 °C (5 °F) below the lowest expected temperature if the loop must keep running, or less if only burst protection is needed. Closed-loop water-treatment guidance recommends at least 25 % inhibited glycol so that the inhibitors remain effective.
Does glycol reduce the capacity of a coil?
Yes. Glycol mixtures have lower specific heat and higher viscosity than water, so a coil sized for water delivers less duty at the same flow and temperatures. Calculate the coil with the actual fluid and concentration.
Should glycol concentration be given by volume or by weight?
Either can be used, but say which. Published freezing-point tables use both bases, and for propylene glycol the volume and mass percentages do not always match.
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