Mini Split Line Set: What Is It, and What Size Do You Need?

 

Mini splits provide an efficient way to cool and heat a room without the expense and energy losses associated with ductwork. However, one important component of a ductless mini split system is the mini split line set.

In this article, we discuss what mini split line sets are, and how to determine the right size you need.

What is a Mini Split Line Set?

A mini split consists of two separate units: an outdoor unit that houses the condenser, and the indoor units that house the air handler. Connecting these two separate units is the mini split line set.

The mini split line set consists of two semi-flexible copper pipes that transport refrigerant throughout your cooling system. Considering that proper circulation of refrigerant is the whole reason your mini split system is able to cool, the line set’s job is a pretty important one.

Each line set is made up of two pipes:

The large pipe, called a suction line, transports the refrigerant in its gaseous state.

The smaller pipe, called the liquid line, circulates the refrigerant in its liquid state.

Both of these lines, when intended for mini-split HVAC units as opposed to traditional central air systems, are insulated and feature flare connections at each end to ensure a tight, pressure-resistant seal.

The Importance of Choosing the Right Mini Split Line Set

All HVAC copper line sets perform the same function, but for your line set to function as it should, it needs to be the right size. 

Pipes that are too large for your system will result in less pressure within the tubes, causing the slow-moving refrigerant to change states at the wrong time and potentially not function at all. Pipes that are too small for your system will result in excess pressure within the tubes, causing the system to internally flood.

Since mini split line sets cannot be adjusted or resized in width, purchasing the right size line set is crucial if you want your mini-split HVAC system to function properly.

What are the Sizes of Mini Split Line Sets?

The size of a line set is determined by width (uninsulated) and length. Both of these factors are important to consider in determining exactly what size you need for your ductless mini-split system.

Line sets for mini-splits usually come in the following sizes, the first number indicating the uninsulated width of the liquid line, and the second number indicating the uninsulated width of the suction line:

• 1/4” and 3/8”
• 1/4” and 1/2”
• 1/4” and 5/8”
• 3/8” and 5/8”
• 3/8″ and 3/4″

Some specialty systems may feature slightly different sizes, but these are the options you can generally expect to find when shopping for a line set. 

Mini split line set listings will also feature a third number, which indicates the insulation thickness on both the suction and liquid lines. 1/2” insulation is recommended for all systems using R410A refrigerant (which  is the vast majority of all AC units that require refrigerant at present). 

All mini-split line sets offered on our website feature 1/2” insulation.

How to Choose a Mini Split Line Set

Step 1: Look at Manufacturer Specs

The only way to determine which size line set you need is to check with the manufacturer of your unit; they will always know exactly what size each individual AC unit requires. For all ductless mini-split air conditioners for sale at Total Home Supply, we include a list of appropriately sized line set options in the main product listing, so there is never any doubt as to whether you are choosing the correct one. There can even be times that the same indoor unit may require different sized lines when used in a single zone vs. multi zone application.

The reason line set size is unit-specific is because certain systems require more/less refrigerant than others, thus requiring larger/smaller lines. Generally, larger units require larger lines and smaller units, smaller lines, but the system’s engineering and efficiency is important to consider as well — a mini-split air conditioner with high BTU and SEER ratings will require a smaller line than a less-efficient unit, because high-efficiency ACs use less energy and thus require less refrigerant to operate.

Step 2: Determine Length

Once you have determined the required width of your line set, you’ll need to figure out how long your lines need to be. The required length of a line set is unique to each individual installation and simply depends on how far apart the indoor and outdoor units are from one another. 

Line sets are usually offered in 15’, 25’ and 50’ lengths, but some systems can support lines up to 150′, so there should be no problem finding a length suitable to your own needs. 

Lines can also be cut to fit specific installation requirements, so when in doubt, always choose a longer line set than you think you will need. Most manufacturers require a minimum line set length of about 15’. Shorter line sets can cause performance issues. Also keep in mind that each system will also have a maximum line set length that cannot be exceeded.

Step 3: Material Construction

It is important to note that line sets should be made of copper, and only copper. 

Aluminum line sets are a cheaper option, and you will find copper-aluminum (Co-AL) hybrid line sets for sale through some retailers, but we do not recommend them for use. Aluminum is less flexible and less resilient than copper, and so aluminum line sets are more difficult to install and could be prone to leakage. 

Aluminum line sets are also not suited for R410A refrigerant, which, as we’ve mentioned before, is the standard for all cooling products manufactured in recent years. Most mini splits manufactured before January 2023 use R410A. When shopping for a line set, regardless of which size you need, choose all-copper pipes.

Installation

Installing a ductless mini-split HVAC system is an extremely complicated endeavor, and setting up the refrigerant is arguably the most difficult part. For that reason, we do not recommend you try to install line sets yourself. Installing a mini-split system requires extensive electrical knowledge, so for your own personal safety, as well as the safety of the unit, we strongly suggest you hire a professional who will be able to do the job correctly.

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If you have any other questions regarding line sets or other ductless mini-split parts & accessories, please do not hesitate to contact us at 1-877-847-0050 to speak with our qualified sales representatives.

In the market for a new ductless mini split? Check out our free Multi Zone Mini Splits Buying Guide!