How Many Mini Splits Do I Need?

Mini splits are a great option for home cooling, being more efficient and flexible than traditional ducted air conditioning. One of the common questions from homeowners shopping for a mini split is “How many mini splits do I need?”

In this guide, we discuss the zones, capacities, and other considerations you need to pin down just how many mini splits you need, both for the indoor and outdoor units.

How Many Mini Splits Do I Need?

The first thing to consider is: how many rooms or spaces do you need to cool?

For the purposes of mini splits, each room is considered a “zone”. Each zone is serviced by an indoor air handler, and have its own individual temperature distinct from the other zones.

This is where the term “single”, and “multi-zone” mini split comes in:

Single-zone mini split: designed for one room

Multi-zone mini split: comes with multiple indoor units to service multiple rooms.

How many indoor units do I need?

Multi-zone mini splits are available in dual-zone, tri-zone, quad-zone, and 5-zone models, each signifying how many rooms they can handle. Some multi-zone outdoor units can be connected to up to 8 indoor units.

Therefore, the number of indoor units you need depends on how many rooms you want to service.

How many outdoor units do I need?

While indoor units are relatively straightforward, the outdoor unit is another matter. How many outdoor units you need is determined by the total connected capacity of the indoor units.

The capacity of a mini split is measured in British Thermal Units, or BTUs. A single outdoor compressor can be connected to multiple indoor units, provided that their total BTU load falls within the condenser’s capacity. Depending on the model and your planned usage, it is acceptable for the total load of the indoor units to exceed the outdoor rating by up to 30%.

For example, an outdoor condenser rated for 36,000 BTUs may be packaged with four 12,000 BTU indoor units. These indoor units have a combined load of 48,000 BTUs. 

You will notice that the combined load exceeds the outdoor unit’s rating. This is because each indoor unit functions independently, so they can adjust according to need. Unless all rooms are fully occupied in the middle of a heat wave, it’s rare that all units will operate at full capacity simultaneously. So getting a bigger condenser may just be overkill and wasted money.

How to Determine the Right BTU Capacity

To find the BTU capacity needed for the rooms you wish to service, you need to measure the dimensions of each room. The bigger the room, the more BTU capacity you need. 

You can use our convenient BTU calculator to determine the BTU required.

However, bigger isn’t always better, as noted in the above example. You need to take into account home improvements you have made, such as insulation and window placements. In general, good ventilation and improved insulation lowers the power requirements needed to cool and heat the rooms, since factors like air leaks and temperature sinks are minimized.

After determining the rough BTU capacity you need, we recommend consulting with an HVAC professional. They can do a manual J-load calculation to more accurately pinpoint the exact mini split size you need.

10 Steps to Determine the Number of Mini Splits You Need

1. Number of rooms

Mini splits can last for up to 20 years when maintained properly. This means you need to plan your mini split purchase not just on the present layout of your home, but with future additions in mind.

For instance, you may be looking to cool two rooms now, but there might come a time when you want to cool an additional room such as the garage. You will also want to factor future extensions or new rooms.

If such additions are likely, you may want to consider getting a bigger outdoor condenser to handle future indoor units.

2. Sizing

The BTU capacity of a mini split determines how big a room it can service. You will need to measure each room to ensure that you get the right sized mini split that can adequately handle the space.

Check out our Ductless Mini Split Calculator to determine the BTU capacity you need for each room.

3. Room types

Some rooms may need more BTUs than others. Rooms that get a lot of sun or have higher ceilings need more BTUs than the ones indicated by their size. The same goes for the kitchen, due to heat sources like cooktops and refrigerators. 

Refer to the Room Factors in our Mini Split Calculator to see which types of rooms need more BTUs, and by how much.

4. Outdoor Unit Capacity

A 4-ton multi-zone outdoor compressor has a capacity of about 48,000 BTUs. In most cases, the indoor units will not be operating all the same time and using up or exceeding this capacity. 

However, If you have a large home and the total capacity of your indoor units far exceeds the outdoor unit’s rating, you may have to get two outdoor units to split the load.

You also have to take the future into consideration. If you plan to extend the house or create new rooms that will require cooling, such additions may go over the capacity of your outdoor unit. If you plan to enlarge the house or create new spaces, it may be better to future-proof your investment by getting a larger outdoor compressor now.

5. Type of mini split

While mini splits can be categorized as either a single zone or a multi zone, there are many other different models of mini splits available to suit different rooms.

Check out our guide to the Different Types of Mini Split Units to determine which ones are suitable for the spaces you need to service.

6. Airflow

Open spaces and rooms without doors may be serviced by a single mini split that is sufficiently large. If you have an open floor plan, or if you have two rooms that are connected without a door, a single large mini split may be adequate for the space.

The important thing here is that the layout permits free airflow between the rooms, and the indoor unit’s BTU capacity is enough to accommodate their combined square footage. It may be necessary to have more than one indoor unit in large open floor plan spaces for more even coverage.

7. The brand

Mini splits are designed to work only with their own brands. It is not possible to mix and match different brands, since they may not have the same communication protocol.

When choosing a brand of mini split, make sure it can handle future indoor mini splits additions. You’ll also want to see if the brand offers different types of mini splits, from wall-mounted to ceiling and ducted concealed, so that you have different mounting options to suit different rooms.

8. Location

Make sure to factor in the location of the indoor and outdoor units when planning out a system. 

Each system will have a maximum number of line sets to connect the indoor units and outdoor unit. Depending on the layout of your home, it may make sense to have for example a dual zone and tri-zone outdoor unit that can be placed closer to the areas they will be covering, rather than a single quad zone system. This can allow for shorter and easier to route line set runs.

Check out our guide to Mini Split Placement for the optimum locations for your indoor units.

9. Distance

Also related to the location is the distance between the indoor units and outdoor compressor. Depending on the layout of the home, it can be more efficient and thus more cost-effective to have an outdoor unit on each side of your house, instead of trying to connect the maximum number of indoor units -handlers to one outdoor unit.

You need to consider the length of wiring needed to connect the farthest indoor unit to the compressor, as well as the cost of installation.

Before deciding on a set number of indoor and outdoor units, consult with an HVAC contractor on the most cost-effective and efficient way to service the rooms based on the layout of your home.

10. Climate

The local climate can also affect the number of mini splits you need. Colder regions may need more mini-split units for sufficient heating, while warmer climates may require more for adequate cooling. 

Colder climates or those that experience extreme temperature swings will also need cold-rated mini splits certified to work in freezing temperatures.

We hope this guide takes the mystery out of determining how many mini splits you need. At Total Home Supply, we carry the best mini split brands to suit different home sizes, layouts, and needs. We also provide expert advice to make the shopping and selection process easier and trouble-free. When in doubt, feel free to contact us and we’ll ensure you get the right ductless mini split for your home.