What Is a Mini Split Line Set?

A mini split line set is a pair of copper tubes that join an evaporator and condenser in a mini split line set system. The line set connects the indoor and outdoor units, enabling the outdoor unit, or the condenser, to supply refrigerant to the indoor unit, or the evaporator. These solutions use ductless split system technology to reduce the environmental footprint required to deliver conditioned air into the interior space.

Because line sets for mini split systems are highly adaptable and can serve numerous applications, these machines are widely used in residential, commercial and institutional settings. Whether you're looking to implement a heating, ventilation and air conditioning (HVAC) system into a room addition, multifamily housing or a garage, mini split line set installations are your solution.

What Does a Mini Split Line Set Do?

In a mini split line set, one of the lines is always bigger than the other. The reason for this size difference is that the smaller of the two tubes, called the liquid or discharge line, transports the liquid refrigerant to the evaporator, where it draws in heat. The suction line, the larger of the tubes, moves lighter gaseous refrigerant into the condenser again and rejects the heat.

Through this process, the vapor and refrigerant in the lines continually recirculate through the system to deliver the proper heating or cooling, depending on flow direction.

Mini splits and mini split line sets have countless application purposes. Among these purposes, they are most commonly used as retrofit add-ons for houses with non-ducted heating systems like radiant panels, hydronic heating solutions, and wood, propane, and kerosene space heaters. They're also beneficial for small apartments, room additions and distribution ductwork for central heating or air conditioning systems.

Other common uses for ductless line set systems include:

  • Older homes or commercial buildings without existing ductwork.
  • Homes with expensive electrical heat sources.
  • Houses with central heating systems that generate high fuel costs or low operational efficiency.
  • Rooms that aren't regularly occupied.
  • New building constructions in areas with high fuel costs.
  • Areas adjacent to unconditioned spaces where ductwork is exposed to harsh temperatures.
  • Outbuildings like garages, sheds and barns where extending the ductwork or capacity isn't possible.

What Sizes Do Line Sets Come In?

The standard length of a mini split line is 25 feet. This length is the estimated distance between the outdoor condenser and the closest indoor air handler. Though this size is most common, the span between the units can even be less than 15 feet, in which case you'd need a line that's approximately the same length. The longest line length you can acquire for a mini split system is usually around 50 feet, though this length is far too long for most applications.

The minimum length and diameter for a line set depend on the manufacturer, the number of units, the distance between the units and the condenser size. For example, if a manufacturer estimates that most users will have 20 feet of line between their air handler and condenser, they'll likely charge the unit for that amount. This number is the line set's minimum required length. Any less than the minimum length could potentially impact performance.

However, if you need less line length than the manufacturer charged the line set for, you can take some out. Most technicians can successfully remove or add to their refrigerant, especially for split systems.

Your line set's minimum length also relies on your unit type. All appliances are different, and their component spacing and setup play heavily into their size. For example, if you have a condenser coil, package unit and an evaporator that are each beside one another, you won't need a 10-foot length.

How Are Line Sets Installed?

When installing your indoor unit, begin by choosing a wall within the room you want to heat or cool that leads to the outside and is large enough to house the air handler. Don't install the unit in a space where it's blocked by furniture, in direct sunlight or near other heat sources.

After choosing your ideal mini split unit location, adhere to the following steps:

  1. Mount the plate directly to the studs. Make sure the mounting hole locations align with the standard stud layout and that there are no ducts, pipes, wires or other obstructions inside the wall.
  2. Use a level to place your wall brackets with optimal alignment. Positioning your brackets properly ensures adequate draining and operation.
  3. Drill pilot holes into the wall using a bit that's slightly smaller than your screw shafts. If you can't reach a stud, use hollow drywall anchors rated for your unit weight to secure the wall brackets.
  4. Drill a hole into the wall for your refrigerant lines, control lines and drain tubing based on the positioning of the mounting bracket. Then, drill a downward-angled hole the size of the pilot bit that's long enough to exit through the home's exterior for proper hole saw alignment.
  5. Connect the control wire to the indoor unit. Check your installation manual for precise instructions based on your mini split model.
  6. Unfold the refrigerant pipe. Push it through the hole in your wall, using electric tape to adhere the refrigerant pipe, drainage tubing and control wire together.
  7. Align the indoor unit with the mount. Feed the bundled tubing, wires and pipes through the hole before securing the unit.

Once you've mounted the indoor unit, it's time to install the outdoor unit. Begin by choosing an installation location either on the ground, an outside wall or the roof. After mounting the condenser, connect the indoor unit's pipes and tubing to the outside unit. Be sure to attach the lines to the exterior wall to keep them in place. Finally, connect the designated pipe joint to the line set located on the backside of your outdoor unit. Then, attach the multiconductor wiring between both units.

What Are Line Sets Made Of?

Refrigerant line sets are comprised of semi-flexible copper tubing. They often use ethylene propylene diene monomer (EPDM), elastomeric or coated elastomeric insulation materials. Line set insulation typically uses an ultraviolet (UV) retardant, but you can apply an additional coating to the materials for greater endurance against long-term exposure.

How Many Line Sets Are Required?

How many line sets your mini split unit requires depends on your zoned HVAC system. There are two primary types of HVAC systems — single-zone and multizone.


Single-zone mini split systems use one condenser and one handler to control a single room, minimizing energy consumption for less expensive, more environmentally friendly use. Single-zones are ideal for room additions, such as attic or basement conversions that don't require system redesigns. When combined with existing central heating and cooling solutions, single-zone systems eliminate the need for upgrades.

With single-zone ductless mini split line systems, you can experience:

  • Lower energy bills.
  • Lower installation costs.
  • Greater sustainability.
  • Less required equipment.
  • Fewer maintenance and repair needs.
  • Better overall performance.


Multizone installations include one outdoor condenser and numerous indoor air handlers. One condenser can manage up to eight indoor units at once, making them ideal for multi-story residences.

The primary benefit of multizone systems is that they enable users to temperature-control separate areas within one house using multiple thermostats. These individualized heating and cooling capabilities minimize central heating exertion and enhance overall comfort for residents. In addition, empty rooms will not waste power or boost energy bills.

Other advantages of using multi-zone mini split line systems include:

  • Less expensive maintenance.
  • Remote management capabilities.
  • Fewer outdoor units.
  • Complete control over temperatures.

What Are Some Dos and Don'ts When Routing Your Mini Split Line Set?

With the proper routing, your ductless mini split line sets will keep homeowners comfortable and temperate year-round. That's why it's essential that you know the dos and don'ts of mini split line set routing and installation.

If you're preparing to install ductless line sets into a residence, be sure to keep the following considerations in mind:

  • Refer to your installation manual: Though most mini split systems operate similarly, it's still crucial to review your installation manual to obtain installation instructions specific to your particular unit. These guidelines contain relevant directions and warnings to ensure the best possible routing outcome.
  • Install a new line set: If you find an existing line set connecting the indoor and outdoor units, you should always replace them. These preowned line sets may be incompatibly sized according to manufacturer guidelines.
  • Ensure the proper line set length: It's critical to adhere to the manufacturer's minimum and maximum line set length requirements to avoid an excess of refrigerant charge. Lines that are too long can compromise system performance, while those that are too short can cause the compressor to fail prematurely.
  • Check for leaks: A leaking mini split system can impact operating efficiency and require costly repairs. To avoid leaks, pressure-test the refrigerant lines using nitrogen and a high-pressure regulator as indicated in the manufacturer's manual.
  • Replace electrical wiring: Even if the existing power wiring seems to adhere to the correct electrical requirements, it's a smart practice to install new wiring for both units. This action eliminates the risk of corroded, hidden or faulty wiring splices that can impact system performance.
  • Adhere to the proper clearances: Proper mini split unit location is highly dependent on predetermined clearances to provide adequate airflow through the outdoor unit. An improperly placed unit that doesn't adhere to the minimum unit clearances can result in inhibited airflow, reduced system capacity and even complete equipment failure.
  • Confirm unit location: Before installing an indoor unit for a homeowner, be sure to verify their location preferences. Your ideas for unit location may not reflect the homeowner's, resulting in customer dissatisfaction.
  • Avoid placing units in high-traffic living spaces: An indoor unit located too close to heavily frequented areas can create unwanted noise pollution in the home. It's a good rule of thumb to avoid mini split line set routing that blows air directly toward room occupants.

Do Line Sets Need Insulation?

Though insulation isn't required for mini split lines, they help maximize longevity by protecting piping from harsh outdoor environments using a UV-resistant coating. Refrigerant lines are exposed to numerous external threats, including:

  • Solar radiation.
  • UV degradation.
  • Animal interference.
  • Organic contaminants and mold.
  • Mechanical abuse.
  • Moisture and humidity.
  • Temperature fluctuations.
  • Wind and sand.
  • Atmospheric contamination.

Insulation helps prevent these elements from infiltrating your line sets, promoting longer refrigerant line lifespan and more reliable system performance. However, it's important to note that according to the International Energy Conservation Code, it's mandatory to protect piping installation on exterior line sets. This protection should prevent degradation resulting from sunlight, wind, moisture and equipment maintenance.

When Do Line Sets Need Replacing?

It's vital to replace your mini split refrigerant lines whenever necessary to ensure efficient refrigerant transport between the condensing unit and evaporator coil. Various situations that warrant a line set replacement include:

  • Installing a new air conditioning unit: Your existing line sets may not be rated for your new equipment.
  • Replacing an old unit: Like new unit installations, it's also wise to replace your line sets when switching out an old unit to ensure the highest quality and performance.
  • Upgrading an existing system: Though reusing old copper lines after a system upgrade may seem harmless, these lines may be inadequately sealed from moisture, resulting in motor damage.
  • Detecting signs of refrigerant leakage: If you notice oil stains on your refrigerant lines, they're likely experiencing leaks, which can occur from corrosion, mechanical damage or settlement stress. Replacing your line sets will prevent leakage from occurring.
  • Noticing the presence of kinks: You should replace kinked line sets to prevent leaks and operational issues.

Can You Extend a Mini Split Line Set?

If you want to relocate an indoor or outdoor air conditioning unit, you may realize that your refrigerant line sets aren't the proper length to support your needs. Luckily, there are ways to extend your mini split line set length in these situations.

Air conditioning and refrigeration field service (ACR) copper fittings are useful for easily extending line sets. You can also use copper pipe fittings to lengthen refrigeration tubes without any welding requirements.

If your existing tubing is comprised of soft copper, you can typically stretch it to accommodate your new location by pulling.

What Do You Do With Excess Line Set?

When performing a mini split installation, you may notice that your line sets are too long to fit the distance between the condenser and handler. In this case, you can perform one of two actions — cutting or coiling the line set. However, both measures have potential risks.

Some mini split units specify a minimum line set length, so it's essential that your refrigerant lines meet that minimum. Cutting your lines may also force you to recharge the entire system, though you can shorten some line sets without changing the charge. You can refer to your manual to determine which applies to your unit.

Instead of cutting, you can also choose to coil the excess line and stow it behind the outside condenser unit. However, coiling comes with the risk of trapping oils. You can avoid this risk by laying the coiled lines flat.

Shop Ductless Split Systems Online at Ingram's Water & Air

If you're looking to invest in a high-quality ductless mini split line set for your next HVAC project, Ingram's Water and Air is your go-to destination. We serve our customers with high-performing equipment at the most competitive prices, along with fast, free shipping and lifetime technical support for product installations and maintenance.

Browse our comprehensive selection of ductless split systems online today.

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