Calculating How Many Mini Splits You Need for Optimal Comfort

Comprehensive Guide to Mini Split Installation: Transforming a Garage into a Comfortable Living Space

When it comes to converting a garage or carport into a cozy living space, heating and cooling are critical considerations. As a homeowner or contractor, you may be puzzled by the number of mini-splits required to maintain comfort. This article explains why a single mini-split unit can be sufficient and how to achieve optimal efficiency and comfort. Let’s dive into the details, investigate the key aspects to consider, and walk you through the transformation process.

Understanding the Basics of Mini Splits

Mini-split systems, also known as ductless mini-splits, are HVAC systems that provide both heating and cooling. They consist of an outdoor condenser/compressor and one or more indoor air-handling units. Unlike traditional HVAC systems, mini-splits do not require ductwork, making them an excellent option for remodels or conversions.

Key Features of Mini-Splits

  1. Energy Efficiency: Mini-splits are known for their high efficiency and ability to reduce energy consumption. They can modulate their output to match the required heating or cooling load, conserving energy.
  2. Flexible Installation: These systems are relatively easy to install, especially in spaces that lack existing ductwork.
  3. Zone Control: Mini-splits allow for individual temperature control in different zones or rooms, enhancing comfort and energy efficiency.

Project Overview: Garage Conversion to Living Quarters

We’re examining a project where a garage carport is being remodeled into a one-bedroom, one-bath living space. The area being converted is under 400 square feet, making it crucial to properly size the mini-split system to avoid over- or under-sizing issues.

Initial Assessment

The project includes a main living area, kitchen, bedroom, and bathroom. The entire space benefits from a foam roof and walls insulated with R19 and R13, respectively. Given these insulation levels and the compact size of the area, careful consideration must be taken to select a mini-split unit that will efficiently regulate temperature without causing discomfort or inefficiency.

Choosing the Right Mini-Split Unit

When determining the appropriate mini-split system for this project, several factors must be considered:

  1. Square Footage and Load Calculation:

    • The space is less than 400 square feet, indicating a relatively low heating and cooling load.
    • Foam insulation typically entertains a load of about 1,000 square feet per ton. Therefore, for a space under 400 square feet, we can estimate needing less than 0.4 tons or approximately 4,800 BTUs.
  2. Unit Placement and Airflow:
    • The main goal is to heat and cool the largest part of the space. The chosen location for the wall-mounted air handler is crucial. In this case, it’s positioned in the most open area to promote even air distribution.
    • Open doors and positive constant pressure from the indoor fan, running almost 24/7, help circulate air to adjacent rooms.

Sizing the Mini-Split System

Given the garage’s size and insulation quality, a one-ton (12,000 BTU) mini-split unit is more than adequate. Anything less than 250 square feet generally does not exceed a one-ton capacity. This calculation ensures that the system efficiently modulates between its minimum and maximum output (from 3,000 BTUs up to 15,000 BTUs), adapting to varying load requirements without short cycling.

Installation Process

Pre-Installation Preparations

  1. Indoor Unit Placement:

    • Wall Mount Air Handler: Positioned optimally to ensure maximum air circulation.
    • Rough-In Box: Installed to manage line sets and drains effectively.
  2. Outdoor Unit Placement:
    • Location Selection: Decided based on structural integrity and ease of access. Avoid mounting on old brick walls to prevent damaging the structure.

Running Line Sets and Electrical Work

  • Line Sets: Routed from the indoor unit to the outdoor unit, taking care of insulation and proper connection.
  • Electrical Setup: Includes the installation of a dedicated breaker box and conduit from the outdoor unit. A double pole breaker and appropriate wiring (typically 12/2 for a one-ton unit) are used to ensure safe and efficient operation.

Post-Installation Checks

  1. Airflow Confirmation: Ensuring that the system’s airflow pattern covers the primary area adequately and extends into adjacent rooms when doors are open or vents are undercut.
  2. Temperature Testing: Measuring and confirming even temperature distribution post-installation.

Addressing Potential Issues

Short Cycling and Airflow

Short Cycling: Installing an oversized unit can cause the system to shut off frequently (short cycle), leading to inefficiency and increased wear on the compressor. The chosen one-ton unit ensures long, efficient cycles by maintaining steady airflow and preventing rapid cycling.

Airflow Management: Correct placement of doors and vents facilitates airflow throughout the space. Options include undercutting doors or installing high vents to enhance air movement between rooms.

Overheating Concerns

In some cases, the indoor fan may continue running even after the desired temperature is achieved, causing slight overheating. This can be managed by programming the unit to shut off the indoor fan once the set temperature is met.

Budget Considerations

Cost Efficiency: One primary advantage of using a single mini-split unit is cost savings.

  • Fewer indoor units mean lower equipment, material, and labor costs.
  • Reduced energy consumption leads to lower utility bills.

Comparative Cost Analysis

Installing multiple units for each room significantly increases the overall project cost, encompassing additional units, longer line sets, extra electrical work, and more extensive labor. In contrast, a single mini-split system in this foam-insulated space effectively minimizes expenses without compromising comfort.


The successful installation of a mini-split system in a small, well-insulated space such as a converted garage relies on careful planning, correct sizing, and strategic placement. This project underlines the critical considerations for achieving an efficient and comfortable environment with a single mini-split unit.

Key Takeaways:

  1. Accurate Load Calculation: Essential for selecting the right mini-split unit size, ensuring efficiency, and preventing short cycling.
  2. Strategic Placement: Proper positioning of both indoor and outdoor units optimizes airflow and system performance.
  3. Cost Efficiency: Utilizing foam insulation and a single unit reduces both upfront and operational costs.

Whether you’re a homeowner or a contractor, understanding these principles ensures you can confidently tackle similar projects, delivering comfort and efficiency without unnecessary expenses. For more insights, tips, and guides on HVAC systems, mini-split installations, and related topics, explore our comprehensive resources and expert advice.

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