Photo of man installing a ductless mini split air conditionerAre you wondering how to install a ductless air conditioner?

(Also known as a mini split AC unit.)

If so, this detailed guide is for you.

Setting up a mini split air conditioner is not as difficult as it may seem and you can save a lot of money doing the installation process yourself.

Below, we’ll go over the basics of how to install a mini split air conditioner in your home.

The process happens in five basic stages:

  1. Choosing the right system
  2. Gathering the right tools
  3. Installing the inside unit
  4. Installing the outside unit
  5. Preparing and testing the system

Before You Start

The information below serves as a general all-purpose guide that applies to most ductless air conditioning installations.

However, instructions for how to install a split AC unit can vary across manufacturers, so if you’ve already purchased a system, make sure to check the owner’s manual for specific installation details.

Additionally, even if you plan on doing the installation yourself, you should still bring in an HVAC professional who knows how to install ductless AC units to assist you with the trickier parts of the process.

This includes things like the electrical wiring, flaring the copper connections, pressure testing, and vacuum pumping.

Even if you’re capable of doing all of those things on your own, it may still be worthwhile to hire a professional to at least look over what your completed work.

How to Install a Ductless Air Conditioner

Step 1: Choosing the Right System

Buying the right mini split air conditioner system that’s most suitable for your home (and the space you want to be conditioned) is an important first step.

When you’re shopping for ductless AC units, you’ll find that they come it two setups:

  • Single-Zone Units — This system is designed to cool down one room (or zone) in your home. It consists of an outdoor unit, called a condenser, which is connected to an indoor unit, called an air handler or evaporator, through a thin refrigeration line containing two copper pipes.
  • Multi-Zone Units — This system is specifically designed to condition the air in separate rooms. Multi-zone ductless units have an outdoor condenser that can accommodate multiple indoor air handlers. Each air handler can then be controlled independently, allowing for temperature zoning.

This guide will go over the steps necessary to install a single-zone unit, but, the same information applies to multi-zone ductless systems.

The only difference is that you’ll repeat the steps for installing each additional indoor air handler and running the separate linesets to the outdoor condenser. Depending on the mini split air conditioner unit you buy, you can attach between two to six total indoor air handlers to the single outdoor condenser.

BTU Considerations

Another thing to consider is how powerful your mini split system needs to be in order to condition the air in a particular zone.

Each indoor evaporator unit will have a British Thermal Unit (BTU) number attached to it.

The BTU number indicates the size of the space that the unit can effectively cool down. So, you’ll want to measure the individual square footage for each room that you plan to put an indoor evaporator unit in. Then, choose the correct BTU size for each unit that you’re installing.

Below is a sample chart depicting how the BTU number corresponds to a mini split unit’s cooling capacity.

You can also look at our guide on the best mini split air conditioner models to find the one that’s right for your needs.

Area To Be Cooled (Square Feet)BTU Needed
Up to 250 sq. ft.6,000 BTU
300 to 350 sq. ft.8,000 BTU
350 to 400 sq. ft.9,000 BTU
400 to 450 sq. ft.10,000 BTU
450 to 550 sq. ft.12,000 BTU
550 to 700 sq. ft.14,000 BTU
700 to 1,000 sq. ft.18,000 BTU
1,000 to 1,200 sq. ft.21,000 BTU
1,200 to 1,400 sq. ft.23,000 BTU
1,400 to 1,500 sq. ft.24,000 BTU
Up to 2,700 sq. ft.36,000 BTU

Step 2: Gather the Right Tools

Knowing how to install a mini split air conditioner won’t help you much if you don’t have the right tools on hand to get the job done.

Of course, the tools you’ll need will depend on how much of the process you end up doing.

The following is a pretty comprehensive list made with the assumption that you will be doing practically everything from start to finish:

  • A Drill with an Impact Driver
  • An Adjustable Wrench and Torque Wrench
  • A Level
  • A Hole Saw or Drill Attachment
  • Metric and SAE Hex Keys
  • Insulated Screwdrivers
  • A Wire Stripper

In addition to the tools mentioned above, you may need an assortment of other supplies, such as wiring, electrical tape, sealant, conduit bender and reamer, and a grinder, if youre going to do the full electrical installation part of the job too.

Step 3: Install the Indoor Unit

Now it’s time to install the indoor air handler.

This part of the installation process consists of a few steps:

  1. First take a look at the your ductless AC’s installation manual and check to make sure you have all of the necessary parts, such as supporting brackets and screws.
  2. Determine where you are going to hang the indoor unit. Most indoor units are attached to the wall. Keep in mind that this wall needs to lead to the outside so you can run the refrigerant line to the outdoor condenser. Ideally, you want a location that is free from obstructions, such as furniture, low-hanging light fixtures and beams.
  3. Attach the air handler’s supporting bracket to the wall, using a level to make sure it is hanging straight. You can use a pencil to mark the location of each screw or create small drill holes. Once the bracket is attached, it’s a good idea to mount the indoor unit to ensure that it attaches and hangs properly.
  4. Now you need to drill a hole next to the bracket in your wall for the refrigeration line that will connect to the outdoor unit. You will need to use a hole saw drill bit for this part. The size of the hole will depend on your particular mini-split system, but most holes will be between 2 ½ to 3 ½ inches in diameter. When drilling, you should angle the bit slightly downward to encourage better water drainage from the condensation line.
  5. You now need to set up the electrical wiring that will run between the indoor unit and the outdoor condenser as well as attach a control wire, typically by hand. This step will vary depending on the ductless AC model you’ve purchased. So, you’ll need to read your installation manual to find out the exact process.
  6. Take out the refrigeration pipe and wrap it tightly together with the control wire and drainage tubing using insulation wrap. Then push the lineset through the hole you just drilled into the wall.
  7. Now you need to place and secure your indoor unit on the wall mount.

Step 4: Install the Outdoor Unit

Now that you know how to install a split AC unit air handler inside your home, it’s time to install the outdoor unit.

This process also consists of a few steps:

  1. Determine where you will put your outdoor unit. Depending on the model and the setup of your home, you may be able to install the outside unit on an outer wall, on the ground, or in some cases on your rooftop. Units attached to the wall will have a special bracket (called a pad) that can be adjusted and secured in place with nuts and bolts next to the hole you’ve drilled in the wall.
  2. With the condenser in place, now you can connect the lineset and electrical wiring from your indoor unit to the outside unit. Be sure to consult with your instruction manual to see how these connections are made.
  3. Affix the lineset to the outside wall so they will be held in place. There are special covers you can buy for the lineset that offer greater protection from the elements and are aesthetically nicer.

Once everything is in place, the next step is to run electrical power to the outdoor unit.

The process for electrical wiring and testing is out the scope of this ductless air conditioner installation guide since there are too many variables that come into play during the setup.

To power the mini split AC system, we recommend that you hire an electrician or HVAC professional to finish this part of the job.

Step 5: Test Your AC System

Unless you have the right equipment, this last stage of the installation process should be done by a qualified HVAC professional who knows how to install a mini split air conditioner.

It typically includes pressure testing the system with nitrogen and then vacuuming the nitrogen out.

After that, the valves will be opened to release refrigerant into the system.

In some cases, more refrigerant may need to be added, which is best left to an HVAC professional to perform.

Finally, you can turn on the electricity to check if the system is properly conditioning the air.

This concludes our guide on how to install ductless air conditioner systems on your own. For more information and reviews on different mini-split models, be sure to check out our guide on the best mini split air conditioner models to find the model that’s right for you.