Mini Split Installation: A Complete How-To Guide

A mini split system offers a sleek and efficient way to heat or cool individual rooms in your home without the need for bulky ductwork. Ductless mini split installations have become a favorite among homeowners thanks to their straightforward setup that causes minimal disruption to your living space. If you're the hands-on type and want to tackle the installation yourself, this guide will walk you through every step of the process.

What Is a Ductless Mini Split?

At its core, a mini split system is both a cooling and heating solution that operates using advanced heat pump technology. By connecting an indoor air handler to an outdoor condenser unit (sometimes called a compressor), it becomes possible to regulate the temperature of multiple zones in your home independently. Unlike traditional central air conditioning, a ductless unit doesn't require air ducts. Instead, a small line set passes through a modest opening in the wall to carry refrigerant and connect the indoor and outdoor components. This makes mini splits an excellent choice for homes without existing ductwork, room additions, garages, workshops, and any space where running ducts would be impractical or costly.

How to Install a Mini Split

When it comes to mini split installation, keep in mind that specific instructions can vary between different manufacturers. Always refer to the supplied manual for details on wiring configurations and model-specific procedures.

Tools & Materials

For a typical mini split installation, you will need the following:

Choose the Right System

Before you head to the store for your ductless split AC, it's essential to select a unit that correctly matches the size of your space. Mini split systems use a measurement called British Thermal Units (BTU), which indicates the cooling and heating capacity of the system. A higher BTU rating means a greater capacity. Start by calculating the square footage of the room so you can pick a system that's properly suited for that area. Whether you base your selection on room size or BTU rating, it's crucial to choose a correctly sized ductless split AC. A unit that's too small won't cool or heat effectively, and one that's too large will cycle on and off excessively — leading to unnecessary wear and higher energy bills. Most manufacturers provide handy sizing guides to help you make the right call.

Install the Indoor Unit

Once you have the correct unit, you can begin installing it indoors.

Choose the Wall: Start by selecting a wall in the room where you plan to mount the air handler. Make sure the wall leads to the outside to allow for the refrigerant and power lines to connect through. Verify that the wall you've chosen has sufficient space to hold the air handler and is clear of any obstructions like shelves or light fixtures.

The air handler should maintain a distance of at least 6 feet from the floor to the bottom of the unit. Follow your manufacturer's guidelines for the exact recommended height.

Also confirm that the exterior wall is free from obstructions where you'll run lines from the indoors to the outdoor unit through the wall.

Locate the Studs: It's best to install the indoor air handler plate directly onto wall studs, so be sure to locate them using a stud finder before mounting.

Verify that the mounting hole locations align with the mounting bracket from the mounting kit supplied with your unit. You'll also want to confirm there are no pipes, ducts, wires, or other obstacles within the wall that may cause complications. Then position the bracket flat against the wall and use a level to ensure it's straight — an uneven bracket can cause the drain to function improperly.

Mark the mounting points on the wall and begin by drilling pilot holes with a drill bit that is slightly narrower than the shank of the wall anchors being used.

Drill the Holes: Drill a pilot hole in the wall for the line set (refrigerant lines, drain tubing, and control lines). You can use the mounting bracket to mark this hole — typically on the lower left or lower right corner. The width of the hole depends on the lines provided but is usually around 2 to 3 inches. Some air handlers give you the choice of which side the lines will exit from — check your manufacturer's instructions to learn how to adjust the housing.

Drill a hole the size of the hole saw's pilot bit, then enlarge it to match the exterior of the house at a slightly downward angle. This ensures that you'll be able to tilt the larger hole you drill with the hole saw. Target a hole size of 2 to 3 inches, angling it gently downward for better drainage.

Confirm that the exterior side is clean and free of debris. Use line set hooks and tilt the pipes slightly downward to the outside so the condenser can drain correctly.

Connect with Wires: Connect the control wires and run the line set to your indoor unit according to the manufacturer's instructions. Usually this requires the removal of the front access panel in order to attach them by hand.

Unlink and push the refrigerant line through the hole and use elastic tape to keep the refrigerant pipe, control wire, and drainage tubing together as a neat bundle.

Raise your indoor air handler and mount it, then connect all the pipes, wires, and tubing through the hole. Then mount the unit securely using the provided screws.

Uncoil the line set from the back of the evaporator and feed it through the hole from inside using an assistant if it helps. Trim the drain line if needed and check to be sure it reaches the condenser. Keep in mind the drain line should be a shorter length of all lines and should pass below the other lines.

 

Install the Outdoor Unit

Once you've finished installing your indoor unit, you can shift your attention to the outdoor condenser.

Choose the Location: Pick a spot where you plan to install your outdoor condenser unit — whether this is on the ground, mounted to a wall, or on a rooftop using appropriate mounting hardware. If you place it on the ground, you'll want to secure it to a condenser pad (which you can either purchase or make from concrete).

Connect Lines: Once you've installed the condenser, you can connect the pipes, wires, and tubes from the indoor unit.

If your kit needs the lines cut and charged, this is the point where you'll need to bring in a licensed professional.

Secure the Wires: Conceal the wires and tubing by adding an external wall cover for a more streamlined look.

Complete the Installation: Connect the correct gauge power line to the line set on the back of the outdoor condenser unit. Then you can connect the multi-conductor cable running from the indoor to the outdoor unit — this is where you will need a torque wrench.

Follow Up With a Professional

Although this is a project you can do yourself, it's a smart idea to hire a certified professional to complete the final technical steps of your mini split system. They will be able to ensure your connections are secure and handle all degrees of gases and such. It's also a good idea to get a licensed electrician to power the unit, as you will need to run a line from the breaker panel to a disconnect switch and then from the switch to the unit.

This guide is provided for informational purposes only. Always consult a licensed HVAC professional for refrigerant handling and electrical connections. Follow all local building codes and manufacturer instructions.