If you value efficiency, savings, and reliability above all else, you should consider installing a single or multi-zone mini-split system in your home. Unfortunately, most people don’t fully understand how mini-splits work or how to decide how many you need.
The amount of ductless mini-split systems you need in your home is dependent on several factors. The size of your home, the ceiling height, the number of rooms, and many other things play a role in your final decision. The same goes for deciding between a single-zone versus a multi-zone setup. As a rule of thumb, you can expect to heat or cool about 500-600 SF per 12,000BTUs. A multi-zone mini-split can have between two and eight indoor unit options.
Choosing the right amount and correct size of ductless units for your home is difficult but crucial. Installing a system that’s too big or small will have detrimental effects on your home and utility bills. Luckily, we’re here to help! We’ll walk you through everything you need to know about ductless mini-splits, both single and multi-zone systems.
How is the Output of a Mini-Split Measured?
Before deciding how many mini-splits or the type of system you need, you first have to know what to look for. Mini-splits are somewhat confusing because the indoor and outdoor units are often similar in physical size, regardless of their heating and cooling power.
Therefore, rather than physical size, there are a few other things you should pay attention to.
BTU stands for British Thermal Unit. It is the standard thermal energy measurement and applies to furnaces and mini-splits. Essentially, a BTU refers to the amount of heat it will take to raise the temperature of a pound of water by a single degree.
Although BTUs traditionally only refer to heat, they apply to heating and cooling power with heat pumps and mini-splits.
The higher the BTU rating for mini-splits, the more powerful the appliance is. Mini-splits with higher BTU ratings will have more operating power and heat up or cool down a room faster than those with low BTU ratings. Therefore, the larger the room or home is that you’re conditioning with a mini-split, the higher the BTU rating should be.
The amount of BTUs you need to keep your home comfortable will help you know what size and how many mini-splits you need.
When choosing your mini-split system, the second thing you should look at is the SEER rating. SEER stands for seasonal energy efficiency rating and refers to your mini-split efficiency. The higher the SEER rating, the less electricity it uses to power the unit, which means the cheaper they are to operate.
As a general rule, the SEER rating tends to go down as the BTU rating increases. Mini-splits that require more power to operate take up more electricity. You should also expect the SEER rating to go down the colder it gets outside during the winter months.
Difference Between a Single and Multi-Zone Mini Splits
Now that you understand how mini-splits get sized according to their heating and cooling power, let’s look at the difference between a single-zone system and a multi-zone system.
Single Mini-Split System
This type of system operates with one indoor air handler and one outdoor compressor. Single ductless systems typically get used to heat and cool a single room in your home or for large, open areas such as shops or garages. If you want to condition your entire home with single-zone systems, you’ll require multiple mini-splits throughout the structure.
Multi-Zone Mini-Split System
Multi-zone ductless systems are where you have a single outdoor compressor that powers multiple indoor air handlers. The indoor air handling unit is often referred to as a wall-mounted unit. Other indoor options include ceiling cassettes, more common in commercial settings like restaurants and offices.
Manufacturers such as Mitsubishi and Fujitsu offer multi-zone units where one outdoor unit can power up to eight separate indoor units. However, keep in mind that each of the indoor units is relatively small, as the accumulation of all their BTUs should match up with the BTU rating of the outdoor unit.
How Does a Multi-Zone Mini-Split Heat Pump Work?
Multi-zone setups for mini-split units are more complicated than a simple single-zone setup. A multi-zone ductless mini-split heat pump system may be perfect for your house, but you still have to decide how many zones you need.
The minimum amount of indoor units with a multi-zone setup is two, but you can have as many as eight depending on the BTU rating of the indoor and outdoor units.
For example, if you have a 60,000-BTU mini-split multi-zone system, there are many variations you can use. You could opt for three 20,000-BTU indoor units, which equals 60,000. Or, you could have two 18,000-BTU units and one 24,000 BTU unit. You could even do eight 7,500-BTU units, which also equals 60,000 BTUs.
However, there are times when you can have more BTUs inside than you do outside. For example, you could optionally have a 12,000 BTU head unit in your living room, a 10,000 BTU unit in your bedroom, and a 15,000 BTU unit in your kitchen/dining area. While this totals out to 37,000 BTUs inside, you could choose to power it with a 30,000 BTU outdoor condenser unit.
Although the totals don’t line up and the inside units require more BTUs than the outdoor unit can handle, this may not be a problem. The outdoor condenser will still supply air to all three indoor units, but they might receive less than they need to cool or heat the area. However, there are very few times when all three indoor units will require full power.
Setting up your multi-zone system in this way is tricky and somewhat risky. You might look back on a cold winter night and kick yourself for not accounting for enough BTUs. Most professional installers will advise against this, but it’s your decision at the end of the day.
Advantages of a Multi-Zone Mini Split
There are several advantages to a multi-zone system, but the main one is that you could save money. If you want to heat and cool your entire home with mini-splits, you’ll likely have to choose between a multi-zone system or multiple single-zone systems. You’ll save money because you’re only paying for a single condenser unit rather than multiple ones.
The time it takes to install a multi-zone system is often less than installing multiple single-zone mini-splits. Rather than setting up multiple outdoor units, you only have to worry about one. And while the SEER rating of a multi-zone system is typically lower than a small single-zone system, you’ll still save on electricity.
A multi-zone ductless mini-split system also allows you to customize the amount of airflow for each room in your house. You can install larger units in bigger rooms and smaller units in ones with less square footage.
Advantages of a Single Mini Split
Better for a Single Room
With a single-zone system, you only have one indoor unit for every outdoor unit. This system is perfect for heating and cooling a large room or space rather than an entire house. Single-zone systems are also ideal if you’re building an addition to your home but don’t want to add extra ductwork.
More Efficient Individually
Single-zone mini-split systems are almost always more efficient than their multi-zone counterparts. The SEER rating for a single mini-split can get as high as 40 or more, whereas multi-zone systems are usually less than half of that. However, if you’re installing multiple single-zone mini-splits, your level of efficiency and savings will decrease by half.
Proper Mini Split Sizing is Crucial
Regardless of the path you choose regarding single-zone versus multi-zone mini-split systems, it’s paramount that you size your units correctly. There are disadvantages to having a mini-split system that’s too big for your room or home, but there are also disadvantages to having a system that’s too small.
What are the Risks of Not Having Enough Mini-Splits?
Anytime that you don’t have enough heating and cooling in your home, you’re bound to be uncomfortable. Insufficient heating and cooling apply to either a multi-zone system where the indoor units are too big for the outdoor units or a single-zone system that isn’t big enough. It can also apply to having one single-zone system when you should have multiple ones or a multi-zone system instead.
Installing mini-splits that are too small is tempting to save money on ductless installations, but it won’t pay off. Your mini-split system will end up overworking itself and increase energy consumption, and it also runs the risk of mechanical failure. You also won’t save money because the increased energy usage and longer running time mean higher energy bills.
What are the Risks of Having Too Many Mini-Splits?
If you have too many mini-splits or a single unit that’s too large, you’ll also have a problem. While your system won’t have trouble raising or lowering the temperature to your liking, it will be ineffective in other ways. The dual purpose of an air conditioner during the summer is to lower the temperature, but it’s also supposed to remove humidity.
If the temperature gets lowered too quickly, the system will satisfy and stop blowing cold air. When this happens, the mini-split will no longer remove humidity. While the temperature may be low, the humidity will be high, and your home will be uncomfortable.
How to Size Your Home for Mini-Split Systems
The square footage is the most important thing to consider when sizing up your home for mini-splits. If you’re installing a multi-zone system, you should consider the square footage of each room that will get an indoor head unit. Here’s how it works.
- Measure the length and the width of the room to calculate the square footage.
- If your bedroom is 20′ x 20′, that equals 400 square feet.
- Next, take the square footage and multiply it by 25.
- That total comes out to 10,000, which is the amount of BTUs your room requires.
Keep in mind that this is a rule of thumb, but it’s largely what a professional HVAC technician will go by. However, they’ll also factor in windows, ceiling height, and other details. For this reason, it’s always better to hire a professional to help you size your home for mini-splits. You may be able to get close, but they’ll be able to get the installation exactly right.
If you’re dead set on sizing your home for mini-splits by yourself, here’s a table with a rule of thumb about how to calculate the BTUs of your home.
|Room or Area Size in Square Feet||BTUs Needed|
|150 – 300||6,000|
|300 – 500||9,000|
|400 – 650||12,000|
|500 – 800||15,000|
|600 – 1,000||18,000|
|1,000 – 1,500||25,000|
|1,250 – 1,750||30,000|
|1,500 – 2,000||36,000|
|2,000 – 2,500||42,000|
|2,500 – 3,000||48,000|
|3,000 – 3,500||56,000|
|3,500 – 4,200 +||60,000 +|
As you can see, the larger the area is that you need to condition, the higher your mini-splits BTUs need to be.
How to Choose the Right Type of System
It’s entirely up to you which mini-split system you choose for your home. Unfortunately, homeowners often try to cut corners or save money by installing a small single-zone system or too few indoor units on a multi-zone system. While every room in your home may not require a head unit, they should all get one for maximum comfort.
A good way to think about it is that each indoor unit on a multi-zone system represents what would normally be a register on a ducted HVAC system. Every room should get a register to ensure comfort and ideal conditioning. In the same way, a room dependent on mini-splits to deliver air will likely be uncomfortable if it doesn’t have a head unit within the room.
Therefore, if you’re hoping to heat and cool your entire home with mini-splits, you should invest in a multi-zone system big enough to handle the job.
How many zones do I need for a mini-split system?
As a general rule, you should have one zone for every room. So, if you have a home with six rooms, you should have five or six zones. Smaller rooms such as pantries or laundry rooms don’t require their own zone and often get fed with secondary air from a nearby zone.
How do you determine how many mini-splits you need?
You should calculate the amount of BTUs your home requires and install enough mini-splits to match the number.
How many heads can you put on a mini-split?
The amount of heads you can put on a mini-split depends on the size of the outdoor unit. The minimum amount of heads for a multi-zone system is two, but you can put up to eight heads on a single mini-split system.
How do mini-splits compare to window units?
A mini-split air conditioner is more energy efficient than window units. Mini-splits are Energy Star rated, providing better control over temperature settings and the convenience of remote control operation. Ductless offers improved indoor air quality and quiet operation compared to a window air conditioner.
Mini-splits use heat pump technology to produce energy savings that window units can’t. Operational costs of mini-splits can be as much as 4 times less than window units. While the upfront cost is higher than window units, the long-term operating costs will reduce monthly energy bills.
The lifespan of a mini-split system is 15-20 years, whereas window units only last about 3-5 years.
Are ductless HVAC systems better than central air systems?
Multi-zone mini-splits are better than central air systems in many ways. Central air units require ductwork that runs through an unconditioned space like an attic, basement, or crawl space. It is estimated that a central air conditioning system can have 30% or more energy loss from air leakage through the air ducts.
HVAC ductwork is prone to duct leakage at connection points and through heat energy transfer in unconditioned spaces.
Ductless HVAC systems maintain their efficiency because there are no ducts for air leaks to occur. This is how ductless mini-splits can obtain much higher SEER ratings than traditional systems.
As you can see, sizing your home for mini-splits is a tall task that’s often best left to the pros. However, if you’re determined to go it alone, you have all the information you need in this article. You also have all the information to decide between a single-zone system, multiple single-zone systems, or a multi-zone system.
Regardless of what type of system you choose, you must have your mini-split adequately sized to match the needs of your home.