The Definitive Guide: How Big of a Pad Needed for Mini-Split Installation

When it comes to installing a mini-split system, the size of the concrete pad is a crucial consideration for DIY enthusiasts with advanced hands-on skills. The pad serves as the foundation for the outdoor compressor unit, providing a stable and level surface for optimal performance and longevity. In this comprehensive guide, we’ll delve into the technical details and expert recommendations to ensure you choose the right pad size for your mini-split installation.

Determining the Compressor Dimensions

The first step in determining the pad size is to identify the dimensions of the outdoor compressor unit. Mini-split systems typically come with a range of compressor sizes, and the pad should be slightly larger than the compressor itself. This extra space allows for proper installation, airflow, and maintenance access around the unit.

To get the exact compressor dimensions, refer to the manufacturer’s specifications or consult with a professional HVAC technician. Common compressor sizes for mini-split systems range from 24″ x 24″ to 36″ x 36″, with the most popular being 30″ x 30″.

Concrete Pad Sizing Recommendations

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Based on the compressor dimensions, the recommended concrete pad size should be a few inches larger on each side. This additional space ensures a stable and level foundation, as well as room for proper installation and future maintenance.

Here are some general guidelines for concrete pad sizing:

Compressor Size Recommended Pad Size
24″ x 24″ 30″ x 30″ x 3″
30″ x 30″ 36″ x 36″ x 3″
36″ x 36″ 42″ x 42″ x 3″

It’s important to note that the thickness of the concrete pad is also crucial. A minimum of 3 inches is generally recommended, but the exact thickness may vary depending on the weight of the compressor and local building codes. Always consult the manufacturer’s guidelines or a structural engineer for specific recommendations.

Preparing the Concrete Pad

Once you’ve determined the appropriate pad size, it’s time to prepare the site and pour the concrete. Here are the key steps to ensure a proper and durable concrete pad:

  1. Site Preparation: Clear the area of any debris, vegetation, or uneven ground. Excavate the site to the desired depth, ensuring a stable and level base.

  2. Formwork: Construct a sturdy formwork using wood or metal to contain the concrete and maintain the desired pad dimensions.

  3. Reinforcement: Consider adding steel reinforcement, such as wire mesh or rebar, to the concrete mix to enhance the pad’s strength and durability.

  4. Concrete Pouring: Carefully pour the concrete into the formwork, making sure to distribute it evenly and vibrate the mix to eliminate air pockets.

  5. Finishing: Once the concrete has been poured, use a trowel or float to smooth the surface and create a level, uniform finish.

  6. Curing: Allow the concrete to cure for at least 7 days before proceeding with the mini-split installation. During this time, keep the pad moist to ensure proper curing.

Securing the Compressor Unit

After the concrete pad has cured, it’s time to secure the outdoor compressor unit. Refer to the manufacturer’s instructions for the recommended mounting method, which may involve using anchor bolts or other specialized hardware.

When positioning the compressor, ensure that it is centered on the pad and level. This will not only provide a stable foundation but also optimize airflow and heat dissipation, which are crucial for the system’s efficient operation.

Considerations for Drainage and Accessibility

In addition to the pad size and construction, it’s essential to consider the drainage and accessibility around the mini-split compressor unit. Proper drainage will prevent water accumulation, which can lead to corrosion and other issues.

Ensure that the pad is slightly sloped (1/4 inch per foot) to allow water to drain away from the compressor. Additionally, leave enough clearance around the unit (at least 24 inches on all sides) to facilitate maintenance, servicing, and airflow.


Choosing the right concrete pad size is a critical step in the successful installation of a mini-split system. By following the guidelines and technical recommendations outlined in this guide, DIY enthusiasts with advanced hands-on skills can ensure a stable, level, and durable foundation for their mini-split compressor unit.

Remember to always consult the manufacturer’s instructions, local building codes, and seek the advice of a professional HVAC technician if you have any doubts or concerns during the installation process.