Multi-zone indoor HVAC units, also known as mini splits, are the most popular alternative to centralized air conditioning units. Unlike traditional air conditioners, multi-zone mini splits do not require ducts to function, making them ideal for use in homes with no existing ductwork.

When properly sized and installed, mini split systems are among the most efficient HVAC systems you can buy for a home or a small office because they offer exceptional temperature control and minimize energy waste.

However, if you want the best results, you must ensure your system has enough capacity and features to heat and cool your house efficiently. Later we’ll list five factors you must consider to help you choose the right multi-zone HVAC unit for your home. First, we’ll get down to some basics.

How Mini Split HVAC Systems Work

Multi-zone mini splits are small air conditioning units that do not need traditional ducting and vents to heat and cool an area.

A complete mini split HVAC unit comprises the following parts:

• An outdoor unit
• Conduits containing the system’s wiring, refrigerant lines, and drain lines
• One or more indoor handler units, each with its own thermostat

Depending on the system’s mode, a mini split may warm or cool the room or zone in which it is installed, making them a practical and flexible HVAC option.

When a mini split system has only one indoor unit, it is called a single zone system. Multi-zone systems have between two and eight indoor handler units. However, the most common configuration is running 4-zone mini splits, allowing you to control the temperature in four areas of your house or business.

Cooling process

• Once turned on and set to the desired temperature, the indoor unit measures the current room temperature. If there is a difference, the unit starts absorbing warm air inside the room or zone, blowing it over the evaporator coils.
• The evaporator coils are connected to the refrigerant lines, causing the warm air to cool down and circulate to the outdoor unit.
• The outdoor unit blows the warm air outside.
• The process continues until the interior temperature has cooled to the desired temperature, at which point the unit cycles down.

Heating process

• Instead of absorbing warm air, the unit pulls cool air from the room or zone.
• The outdoor unit pulls in heat from the outside air, using the refrigerant to absorb it while blowing the cool air outside.
• As the refrigerant line warms up, it sends warmth back into the house.
• The unit continues working until the room or zone has warmed up to the temperature set on the thermostat.

Multi-Zone Mini Split Systems: The Perfect Solution for Your Home

Differences Between Mini Splits and Central HVAC

The main difference between a mini split and a central HVAC unit is how much they can heat or cool at once.

Although central HVAC units can cover a larger surface than mini splits, the primary disadvantage of these systems is that they heat or cool every room inside the house or building simultaneously, regardless of room occupancy. While this may make sense in offices, commercial buildings, or large homes with high occupancy, it is very inefficient in a typical home, as you are unlikely to use every room at the same time. 

Mini splits are smaller, more energy-efficient, and allow you greater control over the temperature in the most frequented areas of your house. Each indoor unit works in the rooms where air conditioning and temperature control are needed, keeping the rooms you use the most at the ideal temperature without wasting energy on the parts of your house you don’t visit often.

How Mini Split Power Is Measured: BTUs and Tons

Mini split systems come in different sizes and capacities. Each system is designed to cover a specific area measured in square feet (ft²). However, when looking at the specs of a specific mini split model, you won’t usually find an accurate area measurement. Instead, you will find a BTU value and a tonnage value.

BTU stands for British Thermal Unit and is a unit of measurement of heat. 1 BTU corresponds to the amount of heat needed to increase the temperature of 1 lb. (455 mL) of water by 1°F.

In the context of HVAC and room heating and cooling, the more BTUs a mini split system has, the higher its heating power and the larger the area it can efficiently warm up.

Each mini split system also has a tonnage value, which refers to its ability to remove heat from a room. The higher the tonnage value, the more powerful the cooling capability is. Tonnage is consistent with BTU capacity; if you choose the right BTUs for your house, your system will also provide you with adequate tonnage.

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The Top Five Ways to Help You Pick the Right Unit

Not all multi-zone mini split systems are created equal. To get the most out of your investment, here are the top ways to find the ideal mini split for your home, maximizing its efficiency.

1. Find out how many zones you need.

The most critical question you need to ask yourself before buying a mini split HVAC system is, “How many rooms of my house need temperature control?”

The answer should equal whichever rooms the occupants use the most frequently. Most users choose to install indoor units in the bedrooms, the living room, the dining room, and the home office. Of course, if your needs vary, you can choose different rooms.

Once you have determined the number of rooms you wish to keep temperature-controlled, you have the number of zones your mini split system needs.

For example, you have five zones if you have determined you need a mini split unit in two bedrooms, the living room, the home office, and the dining room. So, you will need a five-zone mini split system, such as a Mitsubishi mini split multi-zone system with five indoor units.

2. Match the BTUs to the area.

Once you know how many zones you need, you must determine how many BTUs your mini split needs to provide appropriate cooling and heating.

A mini split system is meant to cover a specific area, each requiring its own BTU value if you want maximum efficiency. In principle, you should match the mini split BTUs with the combined total volume of each zone, which requires knowing precise values (room length, width, and height).

However, you can still get a relatively accurate estimation with just the floor area. The typical rule is to add the square feet in each zone, and then multiply the result by 25 to obtain a recommended BTU number.

For example, if you need a three-zone mini split system and the total floor area in all three rooms equals 1,150 ft², multiplying this number by 25 equals 28,750. A 24,000 BTU system would be insufficient, but a 30,000 BTU may be adequate.

If you select an insufficiently powerful ductless system for your area, it will run continuously at full blast without managing to control the temperature in your zones. This is inefficient and will cause your system to wear out prematurely, all while failing to keep your house at a comfortable temperature.

However, it is critical not to fall into the inexperienced buyer’s trap of thinking that more is always better. The primary risk of choosing too powerful a mini split system for your house is short cycling.

A mini split short cycles when it turns on, runs only briefly, turns off again, and then repeats the cycle overly frequently (typically multiple times in less than an hour). These constant on-off cycles consume more power than a steadily running system, rapidly increasing your energy bills and inducing premature wear and tear on the outside unit.

3. Pay attention to the SEER.

SEER refers to the Seasonal Energy Efficiency Ratio, a unit used to measure the efficiency of an air conditioning system. The SEER rating is equal to the total cooling output (quantity of heat removed) divided by the amount of energy consumed over a year.

The SEER ratio is to HVAC systems what MPG is to motor vehicles: a measure of maximum efficiency intended to give you an idea of the potential savings you can make using this type of system. Like with a car, environmental factors and user error can lead to lower actual efficiency, resulting in more power consumed and less heat removed.

By government mandate, all mini split systems manufactured in 2015 or later must have a minimum SEER rating of 15. However, if you’re concerned about operating costs and keeping your energy bills down, there are numerous advantages to choosing a mini split system with an even higher SEER rating.

The Energy Star program, jointly developed by the Department of Energy (DoE) and the Environmental Protection Agency (EPA), certifies high-efficiency home appliances, HVAC systems, and other power-using equipment, from light bulbs to refrigerators.

A mini split with an Energy Star certification means it has been tested and approved by the government for energy efficiency, often possessing a SEER rating well above the minimum of 15.

Every point above the minimum of 15 means your mini split system will consume less power, translating into higher annual savings. Here’s a quick comparison table to help you visualize the average amount of money you’ll save by choosing a ductless system with a SEER rating over 15:

• SEER 16: 6% savings
• SEER 17: 12%
• SEER 18: 17%
• SEER 19: 21%
• SEER 20: 25%
• SEER 21: 29%
• SEER 22: 32%
• SEER 23: 35%
• SEER 24: 38%
• SEER 25+: 40% or more

4. Adapt the system to the environment.

Not all houses are the same, and many physical and environmental factors can influence your system’s BTU requirements.

• Room height: Air conditioning BTU values assume rooms of average height (around 8 ' tall). If your rooms have a significantly higher ceiling, you’ll need to multiply your BTU requirements to account for the difference. For instance, if your rooms have 10 ' ceilings, they are 25% taller than the average, meaning you will need to increase your BTU requirements by 25%.
• Sunlight: Sunlight exposure can also affect a specific room’s BTU needs. Rooms exposed to significant amounts of sunlight need 10% more BTU. Conversely, shaded rooms with little to no sunlight need 10% less.
• Room type: If one of your zones is a kitchen, a garage, or an attic, add 20%. Add another 20% if your zone has poor insulation.
• Occupancy: If one of your zones is a room frequently occupied by three or more people for extended periods (e.g., a playroom), add 600 BTUs for every person over the first two occupants.
• Weather and environment: If you live in a region where summer temperatures frequently exceed 90°F, add 30%.

5. Look into additional comfort and quality factors.

Quality mini split systems often come with features that can further increase your comfort level. Look for models that offer as many of the following as possible, including:

• Air filtration system: Mini split indoor units with high-quality air filter systems catch harmful particles and odors, helping you breathe cleaner air and improve your house’s indoor air quality.
• Environmentally friendly refrigerants: Most air conditioning systems use harmful refrigerants, such as R12 or R22. However, models using refrigerants manufactured from recyclable components, such as R410A, are much less dangerous for the ozone layer.
• Thermal imaging sensors: Quality mini splits detect cold and hot spots in the room, directing airflow toward them and leveling the temperature in its zone, improving comfort.
• Mobile applications: Units that let you connect to your home’s mini split system from a mobile application instantly turn your smartphone into a mini split remote control, wherever you are.

Keep Your House Comfortable with ComfortUp

Taking the time to choose the ideal mini split for your needs can keep your house efficiently temperature-controlled year-round, all while also saving you significant amounts of money on your annual energy bills.

At ComfortUp, we pride ourselves on providing our customers with the best mini split ductless systems by leading brands such as Mitsubishi, GREE, and LG, at affordable prices and with high-level customer service. Send us a message via our contact form if you’d like to request a free 30-minute consultation to discuss your multi-zone mini split options or have any questions about our products. 

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