When you install a ductless mini-split AC or heat pump unit in your home or business, one of the most important items you will need to purchase is the line set. This article will help you choose the correct size line set for the particular mini split you are installing.
Terminology Tip: Line set is often written as one word – lineset – especially by HVAC technicians.
What is an AC Line Set?
Since you’re searching for mini split line set size, you probably already know. However, for those wanting a fuller understanding of their HVAC system, here goes: The line set connects the outdoor condenser unit to the indoor evaporator unit and carries the refrigerant that makes the system work.
Most line sets are made of two semi-flexible copper pipes. One pipe is larger, and is called the suction line. The other pipe is smaller, and is called the liquid line – or refrigerant line.
The suction line carries the refrigerant in its gaseous state, while the liquid line carries refrigerant in its liquid state. They are both enclosed in an insulating material, and they both have flare connections at each end to connect the indoor and outdoor units together with a tight, pressure-resistant seal.
Terminology Tip: The liquid line is also known as the high pressure line (aka high side), and it carries refrigerant from indoors to the condensing unit outside; the suction line is the low pressure line (aka low side), and it carries refrigerant from the condenser/compressor to the evaporator.
Mini Split Line Set Size
In order for your ductless mini split AC to function properly, it must be paired with the right sized line set. If the pipes are too large for your system, the pressure within them will be too low. This will result in the refrigerant moving too slowly, producing inadequate heating and cooling. If the pipes are too small for your system, the pressure within them will be too high. This will also result in the system not working properly, and may even damage it.
Since each copper line set is made of pipes of a certain diameter, it is very important to select the proper size line set to match the size of your mini split system. This is the only way to ensure that it will operate correctly and efficiently.
The following sizes are what are commonly required for line sets. The first number is for the outside diameter (OD) of the copper liquid line, and the second number is for the OD of the suction line. Note that this is not the inside diameter of the lines.
- 1/4” x 3/8”
- 1/4” x 1/2”
- 1/4” x 5/8”
- 3/8” x 5/8”
- 3/8″ x 3/4″
This is how you will usually see them listed, although you may also see the two numbers separated by a dash (-). These sizes do not include the insulation, just the copper pipes that carry the refrigerant.
The Right Size Line Set for a Mini Split System
Each manufacturer of a ductless mini split system should supply the information you need to select the proper line set for their unit. However, the following chart also gives the recommended sizes for most mini splits from 9,000 BTU to 36,000 BTU. Remember, the first number is the liquid line; the second is the suction line.
Line set size for 9,000 – 36,000 BTU mini split ac
| BTU | Line Set Size |
|---|---|
| 9,000 BTU | 1/4″ & 3/8″ OD |
| 12,000 BTU | 1/4″ & 1/2″ OD |
| 18,000 BTU | 1/4″ & 1/2″ OD |
| 24,000 BTU | 3/8″ & 5/8″ OD |
| 36,000 BTU | 3/8″ & 5/8″ OD |
If your mini split system’s capacity is rated by the Ton rather than BTU, use the following chart:
What size line set for 1-3 ton mini split ac
| AC Capacity | Line Set Size |
|---|---|
| 1 Ton | 1/4″ & 1/2″ OD |
| 1.5 Ton | 1/4″ & 1/2″ OD |
| 2 Ton | 3/8″ & 5/8″ OD |
| 3 Ton | 3/8″ & 5/8″ OD |
Info Tip: Sometimes the line sets are written using LL and SL designations, such as 1/4 LL x 3/8 SL, or similar.
What about larger mini split systems?
Ductless mini split systems can also be found in 4 and 5 Ton sizes, but these are usually for 5 to 9 zones (indoor units) and require a special “branch box” to distribute the refrigerant to the additional indoor units. The line sets for these are even larger than those listed above. Be sure to consult the manufacturer’s instructions if you are installing one of these large sized units to be sure to get the correct line sets for each indoor unit, and from the outdoor unit to the branch box.
What about very long refrigerant line sets?
Most residential mini split systems have line sets of 50 feet or less. In the rare case the line set must be longer, it might also need to be larger. For example, a 3/8”x5/8” line might need to be increased to a 1/2″x3/4” line.
Mini Split Line Set FAQ’s
Here are common questions related to mini split linesets.
How far from the outdoor unit can my indoor units be?
Line sets are usually found in lengths of 16, 25 and 50 feet. Typically, a mini split system can handle a total line set length of over 100 feet, depending on the model. This is the combined length of one or more line sets attached to one or more indoor units (evaporators). Do not assume that all systems are alike. A 1 Ton Mitsubishi unit may not have the same specifications as a 1 Ton Daikin unit, for example. Be sure to consult the manufacturer’s installation manual for specifics.
However, be aware that longer line sets require additional refrigerant to produce an adequately charged system.
Is there anything special I should be aware of when purchasing a mini split system and line sets?
Here are two very important items:
1). Make sure you know the proper size unit you need for the building or rooms you want your mini split to serve. Buying a unit too small will result in inefficient cooling (and heating if you have a heat pump). Buying a unit that is too large may simply be “overkill” and a waste of money since the price of larger units is usually more than the smaller ones.
2). Be aware of the type of refrigerant the system and line sets contain. Prior to 2010, most – if not all – central air conditioners, heat pumps, mini-splits, car AC systems, and other refrigeration equipment all used R22 refrigerant.
This type of refrigerant was known to contribute to the depletion of the Earth’s ozone layer. By January, 2020, it was supposed to be completely phased out, and all new systems now manufactured to use R-410A or some other types of refrigerants such as R32, which are supposed to have less impact on the environment.
Be sure to check on the label of any AC unit or line split before you purchase it to make sure it does not use R-22 as its refrigerant.
What if my R22 system needs a new line set or refrigerant charge?
We recommend replacing it if it needs a refrigerant charge. First, it is getting old. Secondly, R22 can still be sold, though not manufactured, and existing supplies are very expensive.
