How Many Mini Splits Do I Need? Posted on July 12, 2023 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. What is a Mini Split? A mini split is a type of air conditioning system that uses a split design, consisting of an indoor and outdoor unit. Also known as ductless mini splits, they don’t require ducts like most ducted AC systems. Instead, they use a small conduit to connect the power and refrigerant lines between the indoor and outdoor unit. This makes mini splits much easier and cheaper to install. It also makes them more efficient, since ducts account for up to 40% of energy losses in conventional ducted AC systems. How Many Mini Splits Do I Need? This depends on how many rooms or spaces you need to cool. Each room can be considered a “zone”, and can have its own individual temperature distinct from the other zones. That’s why there you hear the term “single”, and “multi-zone” mini split, where a single-zone mini split is designed for one room, while multi-zone mini splits can handle multiple rooms. How many indoor units do I need? Multi-zone mini splits are available in dual-zone, trizone, quadzone, 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. Multi-zone units allow you to connect multiple indoor units provided that their total BTU load falls within the outdoor condenser’s capacity. Depending on the model and your planned useage, it is often 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, for 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. Your specific use case must be considered. If you are using the system for bedrooms that will all be occupied at once, it may be best to choose an outdoor unit that more closely matches the BTU needs of the indoor units. If you are splitting the indoor units between living and sleeping spaces, it may be easier to exceed the units rated output. Always consult an HVAC professional when planning a mini split installation. What to Consider When Determining the Number of Mini Splits 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 on the future as well. 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, it may be better to get a bigger outdoor condenser that can 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. 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. 6. 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. 7. 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 amount of line sets that can be used 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. Once you choose a mini split system, any future indoor units will need to be compatible with the system. 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. Mickey Luongo Mickey is the resident heating and air conditioning expert with over 15 years of experience in the industry.