Ductless Mini Splits: All You Need to Know

AC Unit mounted to wall with air blowing

In this guide, we will cover all you need to know about ductless mini-split air conditioning systems. These have grown in popularity in the U.S. over the past several years. Mini splits are extremely versatile, effective, and efficient thanks to advantages such as zone cooling, which is one of many aspects we will discuss.

Are you an empty nester or retired, and not using as many rooms in your house? Are members of your household constantly complaining about it being too cold or too hot? Continue reading to learn more about what a ductless system is, how it works, and what types are available. We will also cover the advantages of installing one and provide tips on purchasing the right system and properly maintaining it.

Chapter 1: What Is a Ductless Mini Split System?
Chapter 2:Advantages and Benefits of Mini Split Systems
Chapter 3: Installation and Options
Chapter 4: Buying Guide for Ductless Mini Splits
Chapter 5: Maintenance of Ductless Mini Splits

Air conditioner machine inside office building.

Chapter 1: What Is A Ductless Mini-Split System?

A mini-split HVAC system is split into two parts. It has an outdoor compressor and indoor evaporators (there can be four to as many as eight units designed to cool individual zones). No ductwork is used to distribute air, as there is in a central A/C system. This configuration allows the temperature in individual rooms to be set to your liking.

How Does It Work?

An outdoor compressor pumps pressurized refrigerant through small tubes that are connected to indoor units. These tubes require just a three-inch-wide hole for a small conduit that links the different components. Each indoor evaporator, which serves an individual room, circulates the refrigerant to extract heat from the interior space.

The in-room units do the cooling rather than a centralized system from which air is transported through supply and return ducts. Once the refrigerant returns to the outdoor unit, the heat collected from the interior air is released into the environment. In addition, some systems integrate a heat pump that extracts heat from outside air and transfers it to the interior to warm your indoor space.

Parts of a Ductless Mini-Split A/C System

Four main components make up a ductless system. These include the:

Condensing unit: In a mini-split system, the condenser is placed outside the home or building and includes condenser coils, which are designed to pump cooled/heated refrigerant through specialized tubes. A fan pulls air through the coil to safely dissipate heat energy into the surrounding environment.
Refrigerant lines: These line sets are usually passed through a small three-inch hole in the wall (this avoids extensive drilling). In rare setups, they are run through a window. Refrigerant lines link the outdoor unit to one or more indoor units in the system.
Indoor unit: Releases cold air into the room or space it serves. Although there are many types of indoor units available on the market, the commonality is all are designed to cool or heat a single zone.

Types of Mini Splits

The different types of indoor units can accommodate specific requirements. They all serve the same function but, depending on their configuration, can fit limited space or a particular interior design theme.

Wall-Mounted: The most popular and least expensive indoor unit, a wall-mounted system is available in many types. They can range from 6,000 to 36,000 British Thermal Units (BTUs) and in sizes from 30 to 44 inches wide, 12 to 14 inches tall, and 6 to 10 inches deep. They are best suited for rooms with at least 7- or 8-foot-high walls (and best placed at a height of about 6 feet). The unit must be placed against a level exterior wall, where a 3-inch hole can be drilled to draw the refrigerant lines, drain tube, and electrical wiring.
Ceiling Cassette: An unobtrusive unit installed behind a decorative cassette grill that sits flush with the ceiling, creating a seamless look. No mechanical components are visible. Ceiling recessed cassettes can range up to 48,000 BTU and have four vents, so are best placed in the center of the room. Often installed in commercial settings, they can be installed in a drop ceiling or traditional joust ceiling if there’s enough space (10 to 14 inches of clearance is required). A built-in thermostat adjusts output based on indoor temperature readings.
Concealed Duct: A hybrid unit that uses ductwork to deliver conditioned air through a dropped ceiling, attic, closet, or crawlspace. The ducts can be branched to supply two rooms, where the temperature is controlled by a single thermostat. It’s important to consider the power specifications of the blower when determining the length of the duct run; a stronger blower will be needed for longer runs.
Suspended: If wall space is limited, ceiling-mounted/suspended mini splits are installed out of the way and can cool a large area. They are often used in commercial, recreational, and educational facilities but can work in any large room or open space. The unit is typically suspended from threaded rods, at least eight feet above the floor, and should be near an exterior wall.
Floor-Mounted: This is typically installed where the wall and floorboards meet to produce a more noticeable effect of cooled or warmed air. A floor-mounted unit is usually more visible, but low ceilings or high windows do not impede installation. It is suited for an attic bedroom where a ceiling slant prohibits the use of a wall or ceiling unit. The indoor unit must not be more than 6 inches above the floor on an exterior wall.
Indoor Air-Handler: This enables a mini-split system to be installed in a large home with a multi-zone configuration. It can serve multiple zones, so you don’t need an indoor unit for every room. Although this requires some ductwork, using an indoor air handler can accommodate large areas such as dens and sections of a home where bedrooms are located. The air handler unit can be installed in a basement, utility closet, or crawlspace.

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Chapter 2: Advantages And Benefits Of Mini Split Systems

Mini splits provide numerous advantages over other types of air conditioning systems, such as:

Heating/Cooling Options: Some mini-split systems provide only cooling for multiple zones. Other systems provide heating as well and can provide warmth on a room-by-room basis. They are well-suited for an attic, basement, or sunroom. A mini-split-based heat pump is a highly energy-efficient alterative to traditional heating equipment as it moves rather than creates heat.
Energy Efficiency: Mini splits are among the most energy-efficient HVAC systems. They deliver a more precise level of heating or cooling to where you need it. No energy is wasted by cooling rooms you do not use. By eliminating ductwork, you also avoid the energy loss that can occur with duct leakage; Energy Star estimates up to 30% of air in a duct system is lost through leaks, holes, and poor connections.1 Central air conditioners operate mainly on two settings (“On” and “Off”) that limit control over indoor temperature. However, mini-split systems use an inverter compressor that adjusts motor speed based on energy demand, conserving energy over time. A traditional system also uses more energy during startup, which isn’t the case with a mini-split system that runs more consistently.

Chapter 3: Installation And Options

Mini split air conditioners must be professionally installed as the job requires the installation of refrigerant lines and the drilling of holes in an exterior wall. Many units must be attached to brackets and other hardware. There are a lot of considerations, but a professional installer can help you make important decisions such as picking the right system for your home and accounting for:

Indoor Location Options: Whether you pick a unit that hangs on the wall or from the ceiling depends on the type of home or interior design. Refrigerant lines must reach the unit as well. Choosing an indoor unit also depends on what fits and can accommodate the room. Precise measurements determine where an indoor unit can be placed; they should always be completed before you make a purchase.
Ratings: Air conditioners are rated on different scales based on their energy efficiency. Several different ratings tell you how efficient a model is. The most important ones to look at include:
- Energy Star: The most efficient models are Energy Star-rated. A unit with an Energy Star label must meet strict minimum requirements for contributing to energy savings, which have been determined by the U.S. Environmental Protection Agency (EPA). It can cut heating/cooling costs by as much as 30%. In addition to energy savings, Energy Star is also focused on health and environmental quality.
- EER and SEER: The Energy Efficiency Ratio (EER) measures an A/C system’s energy usage per square foot of cooling; or, the ratio of cooling capacity, in BTUs, to the amount of power used, in watts. The Seasonal Energy Efficiency Ratio (SEER) rates the overall efficiency of the unit by dividing its seasonal cooling output by energy used (in watt-hours). In the U.S., mini-splits must have at least a 13.0 SEER rating.
- Voltage: Matching a mini-split unit’s voltage to that of your electrical system eliminates the risk of circuit breaker trips or fires. It also improves system performance. Compare voltage specifications before choosing a unit. Smaller, single-zone ones typically run on 110-120 V, while larger units run on 220-240 V.

Additional Options and Accessories

Compressor Types: Most outdoor mini-split units have either an inverter or rotary compressor. An inverter compressor uses just enough power to reach the temperature the system was set to and then idles until needed again. A rotary compressor turns on at full power and goes on and off to maintain the set temperature, which can use more energy.
Refrigeration Line Sets: Transport refrigerant in and out of the home. The line set is a pair of copper tubes that link the outdoor condenser and indoor evaporator. One tube is a smaller discharge line for dense liquid refrigerant that can absorb heat; the other is a larger suction line that carries refrigerant in gaseous form back to the condenser. The set must match the system you have, or it will not work properly. For example, a higher BTU system will require a larger diameter line set. Together, both lines form a continuous loop through the system.
Line Set Covers: Protect line sets, drain lines, and wiring from moisture, UV rays, and other elements. Components can include the split line tube, end socket, horizontal/vertical elbows, and socket/coupling. Some covers can be painted to match the décor of your home and the siding of your exterior. Different sizes are often available depending on the brand, condenser size, number of indoor units, and distance between them.

Condensation Lines: Are essential because a buildup of water droplets can eventually cause water damage to walls, floors, ceilings, and furnishings. Vinyl drain tubes are often used with wall- and floor-mounted indoor units. Drain lines are typically sloped downward to remove water via gravity, and run through holes that must be ¼ to ½ inch lower outside than inside to achieve the proper angle.
Drain Pumps: If you can’t rely only on gravity, a condensate drain pump must be installed. Ceiling cassette and concealed ducted units have built-in lift pumps and rigid PVC tubing that can maintain an adequate slope over a longer horizontal distance. With some mini-split systems, multiple units can be connected to the same drain line, depending on their manufacturer specifications, but a drain pump can be used optionally if necessary. In general, a drain pump consists of a reservoir attached to an indoor unit’s drain pan, and a float switch that activates the pump when the water level is high enough. Types of drain pumps include standard devices concealed in a ceiling or wall, high-suction, low-profile, and surface-mounted condensate pumps.
Ceiling Cassette Grills: Decorative grills are generally sold separately but come in a wide range of styles (grill models that match your mini-split system are provided by its manufacturer). Their purpose is to hide the unit by creating a flush surface with the ceiling. A grill may have a sleek appearance. It can also be customized to match your décor or enhance the look of a room.

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Chapter 4: Buying Guide For Ductless Mini Splits

Knowing what ductless mini-split system is right for your home requires many considerations. To help you determine what you need, here are some important factors. They include details on the space that you want to cool and the type of system most suited for it.

Single Zone vs. Multi-Zone: Both types of systems work very similarly, A single-zone ductless split system uses only one outdoor unit and one indoor unit. It is commonly used in a non-ducted bedroom. A single-room unit is convenient but must match the room’s square footage, in terms of power output, to be effective. To cool more of your home, a multi-zone mini split A/C is needed. There is one outdoor unit connected to multiple indoor units, each serving a particular room or zone. Refrigerant lines can serve four or more zones, including those on different floor levels. The outdoor unit can support all interior units, although setting all units to the highest level simultaneously can cause problems.
Size and Power: An indoor ductless unit is designed to deliver a specific level of cooling power, which is identified in BTUs. An indoor unit is easy to size based on the room’s square footage. For a system serving multiple zones, the BTU rating of the indoor and outdoor units must be considered. The BTUs of each system must add up to the total that you need for your home; the power rating should then be 20% higher for poorly insulated zones or ceilings above 8 feet, and 30% higher if outdoor temperatures regularly exceed 90°F. As for determining the number of BTUs you need, first calculate the square footage of a room. A small 150 to 250-square-foot room needs just 6,000 BTUs per hour while a 400 to 450-square-foot room requires 10,000 BTUs to achieve optimal comfort. On the high end, a 1,400 to 1,500 square foot space needs a 24,000 BTU system for effective cooling or heating.

Sunlight and Shade: The amount of sunlight or shade a room receives can determine the type of unit you need. Sunlight adds warmth, so more power is needed to achieve the desired amount of cooling. In general, the BTU rating should be 10% higher. However, a heavily shaded area means you can reduce it by 10% as there’s less heating to counteract.
Average Occupancy: Body heat contributes to the overall temperature of a room, forcing an air conditioner to work harder. If the A/C is not strong enough, the area may be warmer than expected if it’s often occupied by more than two people. The general rule of thumb is to add 600 BTUs for each additional person who uses the room on a regular basis.
Room Function: The type of room, its purpose, and function can determine what type of ductless mini split system you need. Kitchens contain multiple heating appliances. You would therefore want more cooling output to compensate. Add 4,000 BTUs to the total estimate to ensure the system meets your requirements.
Operating Modes: Ductless mini split systems aren’t just for cooling. Common modes you’ll find include heating, which provides comfort during the cooler months. Heating mode can be controlled by setting the thermostat as you do with cooling. Mini split systems are also capable of dehumidifying, operating in fan-only mode, or selecting a mode automatically based on the ambient temperature. In sleep mode, the system can maintain an adequate room temperature while running quietly.
Features: A mini split air conditioning system may incorporate features such as a programmable This lets you set when it turns on and off. You can program settings up to 24 hours in advance, whether you know you’ll be out for a while or want to be cool as soon as you get home from work. Some models allow airflow adjustments by moving the louvers manually or automatically, or by using a remote control. Washable air filters are convenient features. Another option you may encounter is automatic restart, which gets the system going immediately after a power failure. This protects your circuit breaker and retains the last programmed setting when the system resumes operation. A wall monitor can serve as a control panel for the entire system; it lets you change various settings, including room temperature and operating modes.

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Chapter 5: Maintenance Of Ductless Mini-Splits

Your system should be serviced at least twice a year. Routine maintenance helps it run efficiently and can spot potential issues that can be corrected before further damage occurs. These are some of the most essential maintenance tasks to keep your ductless mini-split system running at its best.

Clean the Condenser Coils: Cleaning the coils is a more complicated task than most people are used to. If you’re comfortable completing it without a professional, first turn off the power, which cools the system down and prevents electric shock, and make sure there are at least four feet of clearance, with no obstructions like leaves, branches, or furniture, around the outdoor unit. Once it is off for an hour, clean the coil with a soft, dry cloth, and look for condensation, ice, mold/mildew, and other problems; a mold-preventing or antibacterial agent can be sprayed on as well. For the most part, treat the condenser as a central air conditioning unit. Look at the refrigerant lines, insulation, fan wheel and blower assembly, and other components as well as verify the unit is properly secured to the base. Call a professional if something doesn’t seem right.
Clean/Change Filters: Cleaning or replacing filters (which depends on the type) is the most basic form of maintenance. Filters should be inspected monthly or more frequently depending on use and demand. Replace a dirty and/or old filter or clean it per the manufacturer’s instructions. Some filters can be cleaned with a HEPA vacuum. But make sure to follow all recommendations as a clean filter keeps the system running efficiently, decreases wear, and improves air quality.
Clean IAQ Components: Any components designed to improve indoor air quality should be removed and cleaned on a routine basis. The types of components vary based on the system and manufacturer. Examples include negative ion air purifiers, UV light devices, air scrubbers, and MERV filters. Keeping these components clean is the best way to ensure they provide the best IAQ advantages.
Repair the System If Needed: If the mini-split system is acting up, consult with a trained professional to determine if it needs repairs. Oftentimes, simple problems can be fixed before they turn into more serious, and expensive, issues. You can even prolong the life of the system. Signs that a mini split air conditioner may need repairs include:
- Higher Bills: You might not immediately attribute a higher electrical bill to the condition of your A/C system, but older units become less efficient. A mini-split should last 12 to 15 years. If your unit is relatively new, additional energy consumption can mean many things; there may be a clogged filter, defective equipment, or the system may be short-cycling.
- The Controls Don’t Work: Remote controls most often stop working due to dead batteries. If changing the batteries doesn’t fix the problem, try to turn the unit on manually. If it fails to start, an electrical problem or faulty reversing valve may be to blame. A valve issue may also lead to a lack of cooling.
- No Cool Air: When there’s a refrigerant leak, the system cannot produce cool air. The decrease in cooling capacity may occur gradually over time as refrigerant often leaks slowly. Once it has completely drained, the system can only function as a fan that doesn’t provide temperature control.
- Ice: If the outdoor unit’s cooling coils become icy, it can be due to reduced airflow. The coils may then freeze over. A clogged filter, damaged fan, leak, dirty coil, or faulty thermostat may restrict airflow enough to ice up the coil, which can weigh it down and cause warping.
- Noise: Ductless mini splits are generally quiet. If you hear grinding sounds from an indoor unit, it might have worn motor bearings. The problem should be addressed quickly, or else the air handler motor may overheat and burn out. Banging sounds can be a sign of a serious problem that may lead to system failure.
- Pooling Water: A clogged condensate line cannot drain moisture collected from indoor air. It can cause water to back up, which can form puddles on the floor, trigger mold growth, or cause all types of damage to belongings and building materials.
- Inconsistent Performance: If your ductless A/C is healthy, you’ll have a consistent supply of cool air. But if temperatures are fluctuating, uneven, and don’t match thermostat settings, there is most likely something wrong with the system.

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Contact NEXGEN for Your Ductless Mini Split Needs

NEXGEN is a leading air conditioning and heating contractor in Southern California. We have multiple offices to provide fast and efficient service to our customers in Los Angeles, Orange County, the Inland Empire, and other locations. Whether you’re looking for the latest ductless mini split air conditioning system, need repairs, or are seeking an advanced air purification system, our experienced technicians can provide prompt, courteous, and personalized service. Our team can install the most reliable, energy-efficient, and long-lasting HVAC equipment that’s sized perfectly for your home.

If central air conditioning isn't practical for you, contact us to learn more about ductless mini-split systems and their benefits. Book an appointment online, today!