Finding the right mini split system size and BTU rating can be a daunting task, especially for those who are unfamiliar with HVAC systems. It’s important to choose a mini split system that is appropriately sized for the space to ensure efficient and effective heating or cooling. Factors such as room size, insulation, and local climate all play a role in determining the appropriate BTU rating for a mini split system. In this guide, we will provide tips and guidelines to help you find the right mini split size and BTU rating for your space, so you can enjoy comfortable temperatures year-round without breaking the bank.
What is BTU?
British Thermal Unit is the abbreviation. It is a type of energy used to measure the amount of heat that power plants and appliances produce. It is also employed to describe the energy content of fuels like propane and natural gas. One BTU is the amount of energy needed to raise a pound of water’s temperature by one degree Fahrenheit.
BTU Sizing Chart for Mini Split Systems
When choosing a mini split system for your home or office, it’s essential to consider the size and capacity of the system needed to effectively cool or heat the space. A mini split system that is too small will struggle to maintain the desired temperature, while a system that is too large will waste energy and money.
1. Room Size Vs Capacity Need
The first step in determining the appropriate mini split system size is to calculate the cooling or heating capacity required based on the size of the room. The capacity is measured in British Thermal Units (BTUs) and is a measure of the amount of heat needed to cool or heat the room.
The following table shows the recommended BTU capacity for different room sizes:
| Room Size | BTU Capacity |
| Up to 150 sq. ft. | 5,000 BTUs |
| 150-300 sq. ft. | 6,000 BTUs |
| 300-450 sq. ft. | 9,000 BTUs |
| 450-550 sq. ft. | 12,000 BTUs |
| 550-700 sq. ft. | 14,000 BTUs |
| 700-1,000 sq. ft. | 18,000 BTUs |
| 1,000-1,200 sq. ft. | 21,000 BTUs |
| 1,200-1,400 sq. ft. | 23,000 BTUs |
| 1,400-1,500 sq. ft. | 24,000 BTUs |
2. Mini Split Size and Quantity for Insulated Rooms
In addition to the room size, other factors that affect the mini split system size needed include the insulation of the space and the number of windows and doors. A well-insulated room will require a smaller capacity mini split system compared to a poorly insulated room.
The following table shows the recommended mini split system size and quantity for well-insulated rooms:
| Room Size | BTU Capacity | Mini Split System Size | Number of Systems |
| Up to 150 sq. ft. | 5,000 BTUs | 0.5 ton | 1 |
| 150-300 sq. ft. | 6,000 BTUs | 0.75 ton | 1 |
| 300-450 sq. ft. | 9,000 BTUs | 1 ton | 1 |
| 450-550 sq. ft. | 12,000 BTUs | 1.5 ton | 1 |
| 550-700 sq. ft. | 14,000 BTUs | 2 ton | 1 |
| 700-1,000 sq. ft. | 18,000 BTUs | 2.5 ton | 1 |
| 1,000-1,200 sq. ft. | 21,000 BTUs | 3 ton | 1 |
| 1,200-1,400 sq. ft. | 23,000 BTUs | 3.5 ton | 1 |
| 1,400-1,500 sq. ft. | 24,000 BTUs | 4 ton | 1 |
3. Mini Split Size and Quantity for Non-Insulated Rooms
Mini split system sizing and quantity for non-insulated rooms can differ from that of well-insulated rooms. In non-insulated rooms, larger mini split systems or multiple systems may be necessary to maintain the desired temperature.
The following table displays the recommended mini split system size and quantity for non-insulated rooms:
| Room Size | BTU Capacity | Mini Split System Size | Number of Systems |
| Up to 150 sq. ft. | 5,000 BTUs | 0.75 ton | 1 |
| 150-300 sq. ft. | 6,000 BTUs | 1 ton | 1 |
| 300-450 sq. ft. | 9,000 BTUs | 1.5 ton | 1 |
| 450-550 sq. ft. | 12,000 BTUs | 2 ton | 1 |
| 550-700 sq. ft. | 14,000 BTUs | 2.5 ton | 1 |
| 700-1,000 sq. ft. | 18,000 BTUs | 3 ton | 1 |
| 1,000-1,200 sq. ft. | 21,000 BTUs | 3.5 ton | 1 |
| 1,200-1,400 sq. ft. | 23,000 BTUs | 4 ton | 1 |
| 1,400-1,500 sq. ft. | 24,000 BTUs | 4 ton | 2 |
Note that for larger rooms in non-insulated spaces, it may be necessary to install more than one mini split system to achieve the desired temperature. It’s important to consider all relevant factors when selecting a mini split system to ensure that it is properly sized and capable of effectively cooling or heating the space.
Calculate the Size of Mini Split System
To calculate the size of a mini split system, you will need to determine the room’s square footage and insulation status. Once you have this information, you can use the following formula to determine the approximate BTU (British Thermal Unit) rating needed:
- For insulated rooms: 20-25 BTU per square foot of living space
- For non-insulated rooms: 30-35 BTU per square foot of living space
- For example, if you have a 500 square foot insulated room, you would need a mini split system with a BTU rating of 10,000-12,500 BTU (500 x 20-25).
1. Identify the Capacity Need
You can establish the mini-split system’s capacity requirement once you’ve estimated the approximate BTU rating required for your space. A mini-split system’s capacity is expressed in tonnes (12,000 BTU/h = 1 tonne). By subtracting 12,000 from the BTU rating, one may determine the amount of tonnage required for the space.
2. Choose the Nearest Mini Split Size
Once you have identified the capacity need of the mini-split system, you can then choose the nearest mini-split size available. Most mini-split systems come in a range of sizes, typically measured in BTU/h or tons. A common size range for mini-split systems is 9,000-24,000 BTU/h or 0.75-2 tons.
3. Consider More than one Mini Spit for Large Rooms
For large rooms or rooms with poor insulation, you may need to consider more than one mini-split system to effectively regulate the temperature. It’s important to note that a single mini-split system can only cool or heat a certain area, so be sure to consult with a professional to ensure you get the right system for your needs.
In summary, to calculate the size of a mini split system, you will need to determine the room’s square footage, insulation status, use the formula 20-25 BTU per square foot of living space for insulated rooms, 30-35 BTU per square foot of living space for non-insulated rooms, identify the capacity need of the mini-split system by dividing the BTU rating by 12,000 and choose the nearest mini-split size available. For large rooms or rooms with poor insulation, consider more than one mini-split system to effectively regulate the temperature.
What Happens If you Undersized Mini Split Size?
If you undersize a mini split system, it will not be able to effectively cool or heat the room, leading to a number of problems.
- First, in order to try to attain the specified temperature, the system will have to work harder and operate longer, which will result in increased energy expenses and a shorter lifespan for the device.
- Second, the system will not be able to maintain a consistent temperature in the room, which can cause discomfort for the occupants. The room may feel too warm in the summer or too cool in the winter.
- Third, an undersized mini split system will not be able to remove enough humidity from the air, which can lead to excess moisture and mold growth, especially in humid climates.
- Fourth, an undersized mini split system will not be able to filter the air effectively, which can lead to poor indoor air quality and potential health issues, especially for people with allergies or asthma.
In summary, undersizing a mini split system can lead to higher energy costs, shorter lifespan of the unit, discomfort for the occupants, excess moisture and mold growth, poor indoor air quality and potential health issues. It’s always better to consult with a professional to ensure you get the right size of the system for your needs.
What Happens If you Oversize Mini Split Size?
If you oversize a mini split system, it will also lead to a number of problems.
- First, an oversized mini split system will cool or heat the room too quickly, causing the system to cycle on and off frequently. This is known as short cycling, which can lead to higher energy costs, increased wear and tear on the unit, and a shorter lifespan for the system.
- Second, an oversized mini split system will not be able to maintain a consistent temperature in the room, which can cause discomfort for the occupants. The room may feel too cool in the summer or too warm in the winter.
- Third, an oversized mini split system will remove too much humidity from the air, which can make the room feel uncomfortable and dry. It can also cause damage to woodwork, drywall, and other building materials.
- Fourth, an oversized mini split system will filter the air less effectively, which can lead to poor indoor air quality and potential health issues, especially for people with allergies or asthma.
In summary, oversizing a mini split system can lead to higher energy costs, increased wear and tear on the unit, shorter lifespan of the unit, discomfort for the occupants, dry and uncomfortable room, poor indoor air quality and potential health issues. It’s always better to consult with a professional to ensure you get the right size of the system for your needs.
Factors that affect the Size of Mini Split Size
There are several factors that can affect the size of a mini split system, including:
- Low outdoor air temperature: A mini split system has to work harder to cool or heat a room when the outdoor temperature is very low. This means that a larger mini split system may be needed to effectively cool or heat the room in extremely cold weather.
- More numbers of people at once: The number of people in a room at one time can affect the cooling and heating load on a mini split system. More people in the room will generate more body heat, which can raise the temperature and require a larger mini split system to keep the room comfortable.
- The ceiling is higher than ten feet: A room with high ceilings may appear cooler or warmer than it actually is. In order to efficiently cool or heat a room with a ceiling height of more than 10 feet, a bigger mini split system may be required.
- Exceptionally strong solar heat gain through windows: If a room has a lot of windows or skylights that allow strong sunlight to enter, it can significantly increase the cooling load on a mini split system. This can cause the room to feel warmer than it actually is, and a larger mini split system may be needed to keep the room comfortable.
Low outdoor air temperatures, larger crowd sizes, ceiling heights greater than 10 feet, and very high solar heat gain through windows are all elements that can alter the size of a mini split system. It’s always ideal to seek professional advice and take these things into account to make sure you choose the appropriate size mini split system for your needs.
Conclusion
In conclusion, selecting the right size mini split system is important for ensuring that your home or business stays comfortable and energy efficient. Factors such as room square footage, insulation status, outdoor temperature, number of people in the room, ceiling height and solar heat gain through windows should be taken into consideration when determining the appropriate size of a mini split system.
It’s recommended to use a general rule of thumb of 20-25 BTU per square foot of living space for insulated rooms and 30-35 BTU per square foot of living space for non-insulated rooms as a starting point. It’s also important to consider the number of mini split systems you will need for the room.
It’s important to note that undersizing or oversizing a mini split system can lead to a number of problems such as higher energy costs, increased wear and tear on the unit, shorter lifespan of the unit, discomfort for the occupants, poor indoor air quality and potential health issues.
It’s always better to consult with a professional to ensure you get the right size of the system for your needs, taking into account all the factors mentioned above.
