What is a mini-split?

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A mini-split is a type of air source heat pump – specifically, a ductless HVAC system offering highly efficient heating and cooling. A mini-split heats and cools a specific zone or room in your home, enabling you to cost-effectively manage and maintain temperatures to your comfort levels by room. We'll break down the details of mini-splits, including their components, how they work, how much they cost, and how to know if they're right for you.

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Key takeaways

  • Mini-splits are air source heat pumps that provide zoned heating and cooling without ductwork.

  • Just as with other air source heat pumps, there are two primary components: an indoor unit or units and an outdoor unit.

  • Unlike most other HVAC systems, mini-splits are generally more efficient, save you money on monthly utility bills, are easier to install than systems with ductwork, improve air quality, and are quieter inside.

  • Mini-split pricing varies substantially, but mini-split installation typically costs between $3,000 and $14,500, averaging around $3,000 and $6,000 per indoor unit installed.

  • Mini-splits can be a great addition to a solar project, helping you save even more long term. Visit the EnergySage Marketplace to compare quotes from solar installers near you.

The "mini" in the name comes from the size – these individual units, also known as "heads," are smaller than most traditional AC, boiler, or furnace equipment. The "split" in the name refers to the system being split between the inside and outside of your home. This contrasts with a traditional "packaged" system that includes a single outdoor unit's heating and cooling equipment.

A mini-split has two main components: an indoor unit or evaporator and an outdoor unit or condenser. Lines connect the two to move the refrigerant through the mini-split system, and the indoor units circulate air throughout the room they're located in to either heat or cool. There are single-room and multi-room mini-split systems, and each has the same components, with multi-room systems just connecting multiple zones or rooms to heat and cool a larger area or all of your home. We'll explain each of the major components in more detail:

Indoor unit

The indoor unit is also known as the air handler or head. If you heat and cool multiple zones or rooms, you may have multiple indoor units.  The room air is recirculated through the indoor unit, passing through its filter. This unit has various components, including:

  • Evaporator coils: Refrigerant flows through these, helping to heat or cool the room.

  • Air filter: Air flows through the air filter before it recirculates into the room, capturing dirt particles, pet dander, mold spores, and other allergens. Some of these filters improve indoor air quality while heating and cooling your home.

  • Blower: The circular blower is responsible for drawing in warm air and blowing cool air back into the room. It's quiet compared to the fans of traditional air-conditioning units.

Outdoor unit

The outdoor unit is the condenser/compressor. As the name implies, it sits outside your home and looks like a rectangular box with a large fan inside. The outdoor unit of a mini-split has four main components to it:

  • Compressor: This device pressurizes the refrigerant, converting it from a gas into a liquid. It pumps the liquid refrigerant through refrigerant lines running to your home's indoor unit(s).

  • Condenser coils: Air is blown through them to heat or cool the room.

  • Outdoor fan: This blows air over the condenser coils to keep them cool.

  • Expansion valve: This small valve ensures the high-pressure liquid refrigerant expands immediately and cools down even more before reaching the evaporator (indoor unit).

Lines

Connecting the outdoor unit to any indoor units are three main lines: drain line, electrical line, and refrigerant lines.

Diagram showing the three lines of a mini-split system

Mini-splits are ductless heat pump systems that efficiently transfer air throughout the room or small area you're heating or cooling. The air is recirculated within the room to heat or cool the space. Mini-splits work only for a smaller space, so you'll need additional indoor units if you have larger spaces or multiple rooms to heat and cool.

Cooling

Mini-splits cool your home in warm months through this process, with each room or zone handling its cooling needs through an individual fan and evaporator unit:

1. Warm air is drawn in through the indoor unit.

This step begins with indoor units (air handlers) inside your home.

2. The refrigerant is moved to the condenser or outdoor unit.

This warm air from each indoor unit is then transported to the condenser (outdoor unit) through a series of pipes. There, the warm air moves through coils containing coolant. When the hot, humid air from inside the room comes into contact with the coils, it transfers its energy to them, turning the coolant liquid into gas.

3. The heat is transferred via the outdoor unit's heat exchanger.

Heat energy is moved by the change of state from liquid to gas and back again, helping to cool the air.

4. The cool air is moved into your home.

Finally, the newly cooled refrigerant feeds to the indoor units (air handlers), where it helps cool the room; the temperature drops as this cycle repeats. You can control the temperature of each indoor unit via remote control.

Heating

This process simply runs in the opposite direction to heat your home in colder months. Instead of transferring heat from inside air to outside, as the liquid refrigerant warms through the heat exchanger, it turns to vapor, and the vapor compresses to concentrate the absorbed heat.

Pros and cons of mini-splits

Pros
Cons
FlexibilityHigh upfront cost
Easy installationNeed to be careful to properly size
Both heats and cools your homeAesthetics
Heats and cools individual zones
Saves money on monthly bills
Efficient
Quiet operation

Advantages

Flexibility

Because mini-splits don't require ductwork and you can add indoor units to multiple rooms, you can often more affordably set up a system to heat and cool smaller spaces or additions to your home. Additionally, mini-splits offer a comfortable, efficient, and cost-effective way to supplement an existing air conditioning or heating system without adding a new HVAC system to your entire home.

Easier to install than larger ducted systems

Ductless mini-split systems are usually easier to install since you can design and size them room-by-room. Installation can take as few as one to two days, depending on the number of zones. You also usually have little to no work to replaster or repair walls since most holes for the lines to run are three to four inches in diameter and have minimal, if any, structural impact on your home.

Graphic showing ducted vs ductless mini splits

Provides both heating and cooling

Mini-splits, like other air source heat pumps, provide both heating in cold months like a furnace or boiler and cooling like your air conditioner in one. Other systems usually require that you purchase both. So, suppose you're looking to replace an aging HVAC system or build a new home: while the overall cost of mini-splits may be more, you usually come out ahead when you factor in that you do not have to purchase another separate system to heat or cool your home.

Zoned heating and cooling

You can easily and efficiently heat and cool different rooms of your home separately. So, if you prefer to keep your main bedroom cooler or have a spare room that you don't use often, you can increase or decrease the temperature in each zone accordingly for comfort.

Inside of a house showing mini-splits flexible zone temperature

Saves money on monthly bills

You don't have to heat or cool your entire home, which usually means lower utility bills. For instance, if you spend most of the day in your home office, you may not need to heat or cool some of the other rooms during the day. Some estimates from expert heat pump installers indicate you can save as much as 20 to 40 percent on electrical costs compared to other HVAC systems.

Less energy loss than ducted systems

According to the Department of Energy, the ductwork of central forced air systems can see as much as 30% energy loss, especially if your ducts go through a basement or attic. Since mini-splits don't use ductwork, there's no additional energy used to circulate through ducts. So, more energy can go towards heating and cooling your home.

Quieter operation

Mini-splits are much quieter than many air conditioners inside your home, with the only real noise coming from the unit outside.

Disadvantages

Higher upfront cost

While you typically save money on your monthly utility bills, one main disadvantage of mini splits can be their upfront cost. They sometimes cost almost 30 %more than central systems (not including ductwork) and nearly twice as much as window AC units of similar capacity. However, suppose you're adding ductwork or putting mini-splits in a new home: the upfront costs quickly cancel out compared with other HVAC systems, especially since mini-splits both heat and cool your home.

Proper sizing is critical

It's essential to work with a trusted, vetted HVAC contractor experienced with air source heat pumps to size each indoor unit correctly and determine the best location to install it. Mini-split sizing isn't always as straightforward as other traditional HVAC systems.

If your system is oversized or air handlers are incorrectly placed, it can result in what's known as short cycling. Short cycling is when the cooling cycle becomes much shorter than usual, causing the compressor to turn off and on more often. Increased starting and stopping means less comfort and more wear on the compressor, which means it won't last as long. If you install a system that's too large, it means an increased installation cost and will likely lead to higher monthly utility bills. You can remedy this downside by using an HVAC contractor or plumber experienced in installing air source heat pumps and mini-splits.

Aesthetic of indoor units

While indoor units, or heads, are less obtrusive than window AC units, some people may not like their appearance. They don't usually have the built-in look of a central system, but there are increasing options, as mentioned above, with some that even look like artwork or paintings.

Image of an LG ArtCool heat pump displaying Klimpt's painting 'The Kiss'

Your total cost of a mini-split system depends mainly on the living area you're looking to heat and cool, determining the number of heads you'll need. Like any technology, you can purchase various levels of performance and capacity, so you'll see a range depending on the capacity the mini split can heat or cool. Specific equipment also has higher efficiencies, measured by their Seasonal Energy Efficiency Rating (or SEER) for cooling efficiency and the Heating Seasonal Performance Factor (HSPF) for heating efficiency.

Typically, your mini-split installation will cost between $3,000 and $14,500, averaging between $3,500 and $6,000 per indoor unit installed. However, you'll need to get a contractor experienced in installing mini-splits to quote your estimated costs, and you should get a few quotes to compare prices.

Ensuring your mini-split system is sized correctly is one of the most critical steps. An improperly sized system may not provide enough heating or cooling or might continuously run, wearing out the system before its average lifespan.

When looking into installing mini-splits, you'll need to choose the correct British Thermal Unit per hour capacity (BTU/H) to heat and cool your room. Generally, the larger the room, the more BTUs per hour you'll need to keep that room comfortable. Mini-split systems come in various sizes, so you'll want to find the appropriate BTU/H capacity based on the size of your room or space. Below are some of the most common sizes of mini splits and the square footage they cover:

Determining the BTUs needed for your living area

Approximate BTU Sizing
Square Footage Covered
12,000400 - 650
18,000600 - 1,000
24,000800 - 1,300

Like many energy-efficient solutions, it depends on your home, heating, and cooling needs, existing system setup (e.g., if you already have ductwork), the amount of space you're looking to heat and cool, and your personal preferences. They might be right for you if you meet the following criteria:

  • You don't currently have ductwork throughout your home and are looking to replace an existing or aging HVAC system

  • You're looking for a more efficient way to heat and cool your home while saving money on monthly utility bills

  • You're looking to supplement an existing HVAC system

  • You're looking to provide heating and cooling for a specific section or zone of your home

  • You have solar panels on your home and are looking for ways to electrify more of your energy usage

Because each home is unique, finding a contractor experienced in installing mini splits and air source heat pumps is good. They can help you determine if your home might be a fit and estimate the cost of installing mini-splits. Even if mini-splits aren't suitable for you, you may still be able to heat and cool your home more efficiently with a ducted air source heat pump or a semi-ducted system.

What's the difference between a mini-split and an air conditioner?

There are several differences between mini-splits and air conditioners. The main difference is that a mini-split will heat and cool your home, while an AC unit will only cool it. Also, air containers use ductwork to cool your home through one central unit, whereas mini-splits provide zoned heating and cooling through a system that transfers air between an inside and outside unit. While an AC unit is usually less expensive to install (if you already have ductwork), mini-splits are more efficient and affordable.

How many indoor air handlers can you connect to one mini-split outdoor unit?

Most outdoor units are designed to work with between one and five zones; however, the largest ductless outdoor units may cover up to eight zones depending on the mini-split you purchase. Work with your experienced mini-split contractor to determine your mini-split system's proper design and sizing.

Is a mini split an air source heat pump?

Yes, a mini-split is one type of ductless air source heat pump. Another type of air source heat pump is ducted, using ductwork to transfer air throughout your home. You could also have a short-run ducted system that includes partial ductwork and partially non-ducted heat pumps for the remainder of your home.

Have more questions about air source heat pumps? We answer common heat pump questions in this article.

Installing solar panels allows you to power your entire home, including your mini-splits, with renewable, zero-emissions electricity. Visit the EnergySage Marketplace today to receive quotes from local solar installers (including some who also install air source heat pumps and mini-splits). Have some additional questions about going solar? When you receive quotes, we'll connect you with an Energy Advisor who can answer your questions along the way (free of charge!).

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