How to Properly Install a Ductless Mini-Split System

How to Properly Install a Ductless Mini-Split System

As ductless mini-split systems become a more popular choice for heating and cooling among homeowners, it’s important for contractors to fully understand the proper installation of these units.

Whether you’re a new technician, a veteran looking for a refresher or simply new to ductless mini-split systems, this article will guide you to a successful installation and help you get new units up and running in no time. We’ll provide helpful tips for preinstallation, the required tools for the job and a step-by-step guide for basic installation.


In general, ductless mini-split systems are fairly easy to install, especially in the case of a single unit mounted to an exterior wall. It becomes slightly more complicated as more units are added or if units are placed on interior walls, as you’ll need to work piping through the drywall to the exterior of the house.

While installation isn’t too challenging overall, we offer extensive training to installers and encourage you to take advantage of this. We recommend training before installing any GE or Haier mini-splits. In particular, it’s critical to understand the proper technique of creating a pipe flare and bending a pipe without kinking it. It’s also important to know the right way to check the pressure with nitrogen once the pipe flares are connected.

Most mini-split systems come pre-charged with 25 feet of lineset. If your job requires anything over that, calculate how much refrigerant you need to match the length of the line (we’ll cover this more in a moment). This will ensure the installed system runs as efficiently as possible.

One multi-split system can be installed in three to four hours. You’ll want to allow at least 30 minutes for a system pressure check, although we recommend a full hour for a thorough approach. If possible, give yourself at least one hour to check the vacuum until you get a reading between 150 and 350 microns.

What you need to know before starting

The system’s location — both interior and exterior — is one of the most critical aspects to understand before installation. You’ll want to be certain of where the unit will be mounted on the inside and where the outdoor unit will go. This will ensure proper placement of both units and that you have the necessary amount of tubing and covering before you start the job. It will also help you understand if the outdoor unit needs to be mounted to the exterior or if it will sit flat on the ground.

Your customer may also have a strong preference on which interior unit they prefer. While the wall-mounted mini-split is the most common, they may rather have a floor console, a small ducted unit that can efficiently connect two rooms or a cassette for drop ceilings. Knowing which model they expect will help you better understand the job parameters.

Sizing a ductless mini-split

If ductless mini-splits are a newer product for you, let’s begin with the basics. The best way to start the sizing process is to use information from a nationally accredited organization such as Air Conditioning Contractors of America as a guide. Their official manuals and protocols will help you calculate the necessary cooling for a given space.

Next, you will want to have a good understanding of what the room will be used for. Is it a living room with little activity? Or is it an office where there will be multiple heat-generating computers? These factors will help you know which units to recommend, where they should be installed and what the users can expect from them. Going through these processes will help you calculate the necessary British thermal units to accurately size the system and ensure it will perform effectively.

Tools you’ll need

To complete the installation successfully, make sure you come prepared with the following tools:

  • 45-degree flaring tool
  • Torque wrench to set flare nuts to the right setting
  • Vacuum pump with fresh oil
  • Nitrogen tank with a gauge to pressure test
  • Scale to weigh out your refrigerant and tank
  • Metric tools (make sure you have an adapter to help hook up a vacuum pump and refrigerant bottle)
  • Micron gauge


Once you have the right unit selected and the tools you’ll need, you’re ready to start the installation process. While every job will be different, these are the general steps to successfully install a ductless mini-split system.

Step 1

The indoor unit is usually mounted to the wall about 7 feet from the floor. It should go in a spot that will allow the air to reach as much space as possible. Be sure to avoid installing it on a wall where the wall across from it is only a few feet away (such as the side of a hallway).

Step 2

In most cases, you will need to drill a 2 1/2-inch hole in the wall to run the copper tubing and electrical wires that connect the indoor and outdoor units. Be sure to insulate the copper pipe, keeping the refrigerant from absorbing any heat between the units. The indoor and outdoor units are the only locations where refrigerant tubes should be exposed.

To connect the lineset from the indoor unit to the outdoor unit, use your flaring tool to make a cone-shaped opening on the end of the copper tubing. The lineset is held on with flare nuts. Use a torque wrench to tighten the nuts to the proper specification.

If the length of the lineset is longer than the factory charge in the outdoor unit — usually 25 feet — you’ll need to add some refrigerant to the system. It’s best to weigh this using a scale. Connect a bottle of refrigerant to the valve and add the extra charge while looking at the scale. Each foot of lineset over the factory charge will require 0.2 ounces if the liquid tube (the smaller one) is 1/4 inch. The 3/8-inch tube requires an additional 0.5 ounces of refrigerant per foot.

Step 3

In colder climates, the unit needs to sit 8 inches above the highest snowfall. If this applies to your job, you will need to use a stand to lift the unit off the ground. The outdoor systems are heat pumps, which run to heat the space. During the winter months, the outdoor unit can collect condensate and ice on the coils. Ice can damage the coil or fan blades if it’s not defrosted properly.

Step 4

Once you’ve set the outdoor unit in the right spot and connected the wiring, it’s time to check the system.

To ensure the lineset is tight and won’t leak, perform a pressure check using nitrogen. You’ll want to use up to 500 psi to make sure there are no leaks. If there aren’t any leaks, pull out all the air and nitrogen from the tubing by using a vacuum pump. This process usually takes an hour. You want to pull out enough air to prevent the moisture from interfering with the refrigerant cycle.

Step 5

After completing all of these tasks, you can open the valves and start the system.

To learn more about our line of ductless mini-split systems and their many benefits, please fill out this one-minute form and we’ll reach out to you directly.