Can a Mini Split be Ducted?

A mini-split system, also known as a ductless air conditioner, is a popular choice for home cooling and heating due to its energy efficiency, flexibility, and ease of installation. While mini-splits are typically installed as ductless systems, it is possible to duct a mini-split system, though it is not a common or recommended installation method. In this comprehensive guide, we will explore the technical details, considerations, and best practices for ducting a mini-split system.

Understanding Ducted Mini-Split Systems

Ducted mini-split systems are designed for specific applications where traditional ductwork is required or preferred. These systems consist of an outdoor compressor/condenser unit and one or more indoor air handlers that are connected through refrigerant lines and a condensate drain line. The key difference from a ductless mini-split is that the indoor air handlers are connected to a duct system, allowing the conditioned air to be distributed throughout the home.

Advantages of Ducted Mini-Splits

  1. Flexible Installation: Ducted mini-splits offer more flexibility in terms of indoor unit placement, as the air handlers can be installed in tight spaces or hidden above ceilings or in walls.
  2. Improved Air Distribution: By utilizing ductwork, ducted mini-splits can more effectively distribute conditioned air throughout the home, providing a more even temperature and comfort level.
  3. Aesthetic Appeal: The indoor air handlers of ducted mini-splits are typically smaller and more discreet than their ductless counterparts, making them a more visually appealing option for some homeowners.

Limitations of Ducted Mini-Splits

  1. Reduced Efficiency: Ducted mini-splits tend to have a slightly lower efficiency rating (SEER) compared to ductless mini-splits due to the additional ductwork and air resistance.
  2. Increased Installation Complexity: The design and installation of a ducted mini-split system is more complex, requiring careful planning, load calculations, and ductwork integration.
  3. Higher Costs: Ducted mini-split systems are generally more expensive than ductless mini-splits, both in terms of equipment and installation.
  4. Secondary Heating System Requirement: Ducted mini-splits are not designed to be the sole heating system in a home and must have a secondary heating system for use during colder outdoor temperatures.

Preparing for a Ducted Mini-Split Installation

can a mini split be ductedImage source: Flickr

Before installing a ducted mini-split system, it’s essential to consider several key factors to ensure a successful and efficient installation.

Ductwork Evaluation

  1. Duct Condition: Carefully inspect any existing ductwork to assess its cleanliness, design, and age. Older or poorly maintained ductwork may need to be replaced or thoroughly cleaned before integration with the new mini-split system.
  2. Duct Sizing: Perform a comprehensive duct design and sizing analysis to ensure the ductwork can effectively distribute the airflow from the mini-split air handlers. This may require modifying or expanding the existing ductwork.
  3. Duct Sealing: Properly seal all ductwork connections and joints to minimize air leaks, which can significantly impact the system’s efficiency.

Load Calculations and System Sizing

  1. Load Calculations: Conduct a detailed load calculation using industry-standard methods, such as Manual J, to determine the appropriate size and capacity of the mini-split system.
  2. System Sizing: Select a mini-split system with the correct capacity to match the calculated heating and cooling loads of the home. Oversizing or undersizing the system can lead to inefficient operation and comfort issues.
  3. Blower Door Test: Perform a blower door test to measure the home’s air tightness and identify any air leaks that may need to be addressed before the mini-split installation.

Refrigerant Line Considerations

  1. Line Set Length: Ensure the refrigerant line set length between the outdoor and indoor units does not exceed the manufacturer’s recommended maximum, as this can impact the system’s performance and efficiency.
  2. Line Set Insulation: Properly insulate the refrigerant lines to minimize heat transfer and prevent condensation, which can lead to water damage or mold growth.
  3. Line Set Routing: Plan the routing of the refrigerant lines to minimize bends and ensure they are supported correctly to prevent kinks or damage.

Installing a Ducted Mini-Split System

The installation process for a ducted mini-split system is more complex than a ductless system, requiring specialized knowledge and skills. It’s recommended to have a licensed and experienced HVAC contractor handle the installation to ensure optimal performance and safety.

Indoor Unit Placement

  1. Ceiling Mounting: Ducted mini-split air handlers are typically designed to be installed above a suspended ceiling, allowing the ductwork to be concealed.
  2. Wall Mounting: In some cases, the air handlers can be wall-mounted, but this may require additional ductwork and modifications to the home’s structure.
  3. Accessibility: Ensure the indoor unit is easily accessible for maintenance and servicing, with sufficient clearance around the unit.

Ductwork Integration

  1. Duct Connections: Properly connect the mini-split air handler to the existing ductwork, ensuring a tight and secure fit to prevent air leaks.
  2. Duct Modifications: If necessary, modify the ductwork to accommodate the size and airflow requirements of the mini-split system, such as adding or resizing supply and return ducts.
  3. Duct Insulation: Insulate the ductwork to minimize heat transfer and maintain the system’s efficiency.

Electrical and Controls Integration

  1. Electrical Connections: Properly wire the mini-split system to the home’s electrical system, following all local and national electrical codes.
  2. Thermostat Integration: Install a compatible thermostat or control system to manage the mini-split system’s operation and ensure optimal comfort and energy efficiency.
  3. Condensate Drainage: Properly route the condensate drain line from the indoor unit to an appropriate drainage location, such as a floor drain or exterior of the home.

System Commissioning and Testing

  1. System Startup: Carefully follow the manufacturer’s instructions for starting up the mini-split system, including any required refrigerant charging or system flushing.
  2. Performance Testing: Conduct a thorough performance test to ensure the system is operating within the manufacturer’s specifications, including airflow, temperature, and humidity measurements.
  3. Homeowner Education: Provide the homeowner with detailed instructions on the proper operation and maintenance of the ducted mini-split system, including any necessary filter changes or service requirements.


While it is possible to duct a mini-split system, it is not a typical or recommended installation method. Ducted mini-splits are designed for specific applications and require careful planning, design, and installation to ensure optimal performance and efficiency. Homeowners considering a ducted mini-split system should carefully weigh the advantages and limitations, and work with a licensed HVAC contractor to ensure a successful and long-lasting installation.