What Does Low Ambient Mini Split Mean: A Comprehensive DIY Guide

Low ambient mini splits refer to ductless heating and cooling systems that can operate efficiently in cold temperatures, typically below 50°F (10°C). These systems are designed to maintain their heating capacity even in extreme low-temperature conditions, making them suitable for regions with harsh winters.

Heat Pump Type

Low ambient mini splits often use heat pumps that employ a scroll compressor, which is more efficient and reliable in cold temperatures compared to a reciprocating compressor. Scroll compressors are known for their superior performance, reduced noise levels, and increased durability, especially in low-temperature applications. They utilize a spiral-shaped mechanism that compresses the refrigerant more efficiently, resulting in higher energy efficiency and better heating capacity at low ambient temperatures.

Heat Exchanger

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The heat exchanger in low ambient mini splits is typically made of copper tubing with aluminum fins, which provides better heat transfer and resistance to corrosion. Copper is an excellent conductor of heat, allowing the heat exchanger to efficiently transfer thermal energy between the refrigerant and the surrounding air. The aluminum fins, on the other hand, enhance the surface area of the heat exchanger, further improving heat transfer and overall system performance.

Defrost Cycle

To prevent ice buildup on the outdoor unit, low ambient mini splits use a defrost cycle that reverses the flow of refrigerant, allowing the outdoor coil to warm up and melt any ice accumulation. This process is crucial in maintaining the system’s heating capacity and preventing a reduction in efficiency due to iced-over coils. The defrost cycle is typically triggered by sensors that monitor the temperature and pressure of the refrigerant, ensuring that the system automatically initiates the defrost process when necessary.

Heating Capacity

Low ambient mini splits can maintain their heating capacity down to temperatures as low as -13°F (-25°C). This is achieved through the use of a larger outdoor unit and a more efficient heat pump. The larger outdoor unit provides a greater surface area for heat exchange, allowing the system to extract more heat from the cold outdoor air. Additionally, the use of a more efficient heat pump, often with a variable-speed compressor, ensures that the system can continue to deliver sufficient heating even in extreme cold conditions.

Auxiliary Heating

Some low ambient mini splits come with an auxiliary heating feature that uses electric resistance heaters to supplement the heat pump’s output in extremely cold temperatures. This feature is particularly useful when the outdoor temperature drops below the heat pump’s operating range, ensuring that the indoor space remains comfortable and warm. The auxiliary heating system is typically integrated into the overall control system, allowing for seamless and automatic operation.


To minimize heat loss, low ambient mini splits use thicker insulation on the refrigerant lines and a well-insulated outdoor unit. The insulation helps to maintain the temperature of the refrigerant as it travels between the indoor and outdoor units, preventing heat from being lost to the surrounding environment. This is especially important in cold climates, where the temperature difference between the indoor and outdoor environments can be significant.

Condensate Drainage

In cold temperatures, the condensate produced by the system may freeze in the drain line, potentially causing issues with water backup and system performance. Low ambient mini splits use a condensate drain heater to prevent this from happening. The drain heater, typically an electric heating element, keeps the condensate line warm, ensuring that the water can flow freely and be properly drained away from the system.


Installing a low ambient mini split requires careful planning and execution. The outdoor unit should be installed in a location that is protected from wind and direct sunlight, as these environmental factors can impact the system’s performance. The indoor unit should be mounted on a wall or ceiling that is level and plumb, ensuring proper airflow and efficient heat distribution.


Proper sizing of the mini split system is crucial for efficient operation. A heat load calculation should be performed to determine the correct size of the outdoor unit and the number of indoor units required. This calculation takes into account factors such as the size of the space, insulation levels, and the local climate, ensuring that the system is properly matched to the heating and cooling needs of the building.

By understanding the technical details and specifications of low ambient mini splits, DIY users with advanced hands-on skills can successfully install and maintain these efficient heating and cooling systems, even in regions with harsh winters.


  1. Confused about Low Ambient Mini-splits, please advise – Reddit
  2. Low ambient minisplit heating – GreenBuildingAdvisor
  3. Low Ambient Mini Splits – BMS Controls and Energy