Ductless Line Sets

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Ductless line sets connect the outdoor condenser and the indoor air handler. They are essential to the heating and cooling process of a mini-split as they transport the refrigerant in and out of the indoor and outdoor units. Therefore, it is vital that the ductless installation company selects and installs the line sets correctly. Otherwise, your mini-split will not function as designed.

This article will help you learn all you need to know about the importance of a line set for your mini-split system.

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What Is A Ductless Line Set?

image of a ductless line setA line set consists of two copper tubes that connect the condenser to an indoor air handler. The copper tubes always come in different sizes, with one line larger than the other. The smaller tube is called the liquid or discharge line. It is responsible for transporting the dense liquid refrigerant to the indoor unit where it absorbs heat. On the other hand, the larger tube is the suction line. It carries the gaseous refrigerant to the condenser where it releases the heat.

The liquid and gaseous refrigerant continuously circulate between these two lines to provide you with conditioned air. The direction of the refrigerant depends on whether you need heating or cooling. Simply put, the flow reverses when you need heat.


Single-Zone And Multi-Zone Ductless HVAC System Setups

If your home has a single-zone unit, you only need to buy a single line set. However, if you have multi-zone systems, then you will need to purchase one line set per indoor unit. You also have to take a few things into consideration. These factors include the total line length, distance, and diameter of each set. Otherwise, your system might not function as it should. A professional HVAC contractor can determine this for you before your ductless installation takes place.

There are also a few multi-zone units that need a branch box to provide refrigerant from the condenser to the indoor units. This means that it needs its own line set to connect to the outdoor unit. Branch boxes are manufacturer-specific and, thus, not all branch-box combinations are supported. Therefore, it is vital that you choose your HVAC installation company wisely as they will select the correct branch box for your unit.

The HVAC contractor may also recommend a port adaptor. This helps them make a connection when the diameter line is not the standard fitting on your mini-split. Some homeowners think that these adapters will restrict the refrigerant flow. Rest assured that these adapters are designed to allow the proper flow of refrigerant. With a port adapter, an HVAC contractor does not need to modify the current line you have to make your ductless installation work. These adapters will allow an HVAC contractor to use a correctly-sized line without having to worry about the fitting size.

Keep in mind that the ductless installation company you choose should strictly follow the manufacturer’s recommendations when it comes to the sizing of refrigerant piping connections. This is why installing a ductless mini-split system is not a DIY project and requires the knowledge and experience of a licensed HVAC contractor.

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Ductless Mini-Split Line Set Accessories

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The following are three accessories which are designed to make your mini-split experience easier:

Rectorseal NoKink

This accessory is a flexible connection between the refrigerant line and the mini-split evaporator. Its NoKink technology and three-inch copper stub allow for easy installation. It prevents the refrigerant line from kinking and, in turn, saves time and labor costs. It also helps ensure that your unit is running at optimum efficiency.

Ball Valve

A ball valve is designed to let you easily suspend refrigerant flow without needing to remove the seal cap. It makes servicing the refrigerant lines quick and easy. It also features a Schrader valve for fast charging. This accessory is necessary for multi-zone systems as it lets the system be serviced without having to remove the refrigerant out of the lines.

Line Set Covers

ductless hvac system line set cover

A line set cover is an accessory that hides and protects the copper line set of your mini-split. Without a line set cover, your line set is exposed to elements such as direct sunlight and rain. In fact, UV rays can hasten the deterioration of your line sets. A line set cover acts as a barrier against these elements and protects it from all weather conditions.

A line set cover is also completely paintable. This way, you can match its color to your wall so that it blends in or have it painted in any design you want. This is an excellent perk for when you value your home’s aesthetic.

Line Set Sizing

Line sets come in various sizes. The sizing depends on factors such as the number of evaporators, the mini-split make and model, the distance between units, and the condenser size. The manufacturer predetermines the size of the line set. Therefore, it is recommended that you choose a ductless installation company with enough experience to know the exact sizing requirements needed for the mini-split you purchase.

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image of a ductless mini-split system installation

The size of the line set usually corresponds with the size of your mini-split. It means that the higher the British thermal unit (BTU) or tonnage, the larger the diameter line set needs. The sizes of line sets for mini-splits are indicated by numbers. The first number indicates the diameter of the liquid line, while the second number is the diameter of the suction line. For example, a large line set has a 3/8″ liquid line and a 3/4″ suction line. A smaller line set has a 1/4″ liquid line and a 1/2″ suction line.


The distance is the total maximum line set length needed by your mini-split. This length is vital for the HVAC contractor to determine as it impacts the location of your outdoor and indoor units. Furthermore, when they measure the distance, be sure that they also include the corners and bends in your house. You also have to consider the wall thickness and the vertical rise to get an accurate measurement.

If you choose an inexperienced ductless installer, then you will inevitably encounter an issue after they have installed your mini-split. You might find that they placed the indoor unit too far from the outdoor unit. If this is the case, then your unit will not correctly operate because they exceeded the maximum length required.

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Ductless Refrigerant

The distance between the outdoor and indoor units also affects the refrigerant in the line set. When you purchase a mini-split, it is already charged with the required refrigerant. The factory charge is usually enough for the majority of installations. However, if your unit needs a longer line set then the HVAC contractor might need to add more refrigerant to ensure that your mini-split operates at maximum capacity. The contractor that you hire for your ductless installation should have the experience to know how much additional coolant is needed if this is the case in your home.



Like any other purchase you make, you have to ensure that your HVAC contractor of choice offers you high-quality line sets that are built to last. Check to see if the line set underwent annealing. This is a special heat-treating process that allows the copper to flex without breaking or kinking. You also have to ensure that the product has a manufacturer warranty of at least five years.

High-quality line sets also have flared ends. This makes for easier installation as your HVAC contractor will not need to braze it. Your line set should also come equipped with insulation that is at least half an inch thick. The insulation must also be UL listed for weather resistance and is rated for fire and smoke. All of these assure you that your line set is safe to use.

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Incorrectly Sized Line Sets

When your line sets are improperly sized, then you are bound to encounter some problems. Here are some of the main issues you will have if line sets are either too small or too big:


When the suction line in your line set is too small, then the operating pressure needed is lacking. This will reduce your mini-split system’s capacity and efficiency. It will also most likely lead to lowering your system’s lifespan.

On the other hand, a liquid line that is too small means that both indoor and outdoor units won’t receive the proper amount of refrigerant. This will reduce the unit’s operating pressure as well. When this happens, your system won’t correctly function to its maximum capacity.



A suction-line that is too big means that the refrigerant pressure will be lower than what is necessary. This means that the liquid might not be transported back to the compressor as efficiently. As a result, the compressor will not operate as well as it should because there won’t be enough refrigerant to help the compressor release any heat build-up.

When the liquid line is oversized, it can hold a more considerable amount of refrigerant. However, this shouldn’t be the case. The liquid will only become easily diluted. The compressor, in turn, will end up with major damage due to the lack of refrigerant.



You must have the proper supporting components for your mini-split system to work at optimal performance and operate at maximum efficiency. Therefore, having a properly-sized line set along with the correct installation is critical to your unit’s overall functionality. To be safe and sure, always choose to work with an HVAC company that follows the manufacturer’s guidelines during installation.

A licensed HVAC expert can assist you from start to finish, from buying the right unit and line sets to testing the newly installed mini-split. Rest assured that with professional assistance, your system will soon be providing you with the home comfort you deserve.

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Call Townsend Energy For All Of Your Home Heating And Cooling Needs

te logoIf you are ready to switch to a ductless HVAC system or have more questions, call Townsend Energy today. Our experienced NATE-certified technicians will discuss your needs and requirements to help you find the best ductless HVAC system for you.

Townsend Energy is a full-service HVAC company that services residential and commercial properties throughout New England. We offer a range of heating and cooling services, including HVAC installations, repairs, tune-ups, and more. Our experienced, NATE certified professionals can find the best home heating and cooling solutions for your home while working with your budget. We aim to improve your home’s level of energy efficiency, comfort, and indoor air quality. We back our work by a warranty to ensure your satisfaction. Also, we provide free, in-home estimates. Call Townsend Energy today.

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