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Central Air Installation: A Comprehensive Guide

Are you considering installing central air conditioning in your home? Whether you're building a new house or upgrading your existing system, understanding the process can help you make informed decisions. In this guide, we'll provide...

Are you considering installing central air conditioning in your home? Whether you're building a new house or upgrading your existing system, understanding the process can help you make informed decisions. In this guide, we'll provide you with valuable insights and tips to ensure a successful central air installation.


Before we dive into the details, let's cover a few important terms you need to know.

Central Air Conditioner

Unlike window or wall air conditioners that cool specific areas, a central air conditioner cools air in one location and then distributes it throughout the entire home using the existing furnace's air handling capabilities. Most single-family homes in the U.S. with central air have a split system, which consists of an evaporator coil inside the home and a compressor outside. It's important to note that heat pumps are another form of central air conditioning, but for this guide, we'll focus on connecting central air to a furnace.


When discussing air conditioners, "size" refers to the cooling power of the unit, not its physical dimensions. HVAC professionals use a measure called British thermal units (Btu) to determine the size of an air conditioner. For example, a 2.5 ton air conditioner equals 30,000 Btu. To ensure optimal cooling efficiency, it's crucial to select the right size unit for your home.


The efficiency of an air conditioner is measured by the seasonal energy efficiency ratio (SEER). Higher SEER units are more efficient and consume less energy, especially when the temperature is lower. This makes them a cost-effective choice in the long run.

team of hvac installers repairing central air conditioning system outside of house Image: Team of HVAC installers repairing a central air conditioning system outside of a house.

Can You DIY Central Air Installation?

While we encourage the DIY ethos, central air conditioning installation is a complex project that generally requires professional expertise. Unless you have extensive experience with such projects and possess the necessary skills, it's best to seek professional help. Hiring professionals ensures the installation is done correctly, prevents any potential damage, ensures compliance with permits and licensing requirements, and avoids voiding warranties.

However, if you're determined to take on some of the work yourself, keep in mind that handling the refrigerant will require a licensed professional. In some areas, only a licensed electrician can connect the electrical to the service panel.

Working With Professional HVAC Installers

When working with professional HVAC installers, effective communication is key. Here are some important factors to consider:


Installing central air conditioning is a significant undertaking that requires careful planning. Discuss your priorities with the contractor, whether it's energy efficiency, cost, or specific preferences such as the location of the condenser unit and the type of thermostat you'd like. Also, ensure that the contractor will handle any necessary permits or paperwork.


Determining the right size central air conditioner for your home is essential for optimal performance. An undersized unit will run continuously, while an oversized unit will cool the house too quickly and shut down before completing a full cycle. To determine the correct size, HVAC installers use a calculation called a "Manual-J," which considers various factors specific to your home. However, if you'd like a rough estimate in advance, multiply the square footage of your home's conditioned space by 25 to calculate the required Btu, then divide by 12,000 to determine the tonnage.


Obtain written estimates from multiple vendors to ensure you're getting a fair price. Clarify any doubts and request expense breakouts. Though not all contractors can itemize everything, they should be willing to communicate enough to make you feel comfortable with the process.

two central air conditioning units outside of house Image: Two central air conditioning units installed outside of a house.

The Central Air Installation Process

The installation process typically takes around a day to complete. Here's a summary of the main steps involved:

  • Duct work installation or modification: Depending on your home's existing setup, minimal duct work may be required. If ducts need to be installed, work with your contractor to find ways to hide them and avoid extensive drywall repairs.

  • Interior unit: The evaporator coil is installed inside the furnace plenum, which is the section of the furnace that brings in and sends out air. The evaporator coil is placed in the supply plenum, the outflow of the furnace.

  • Exterior unit: The placement of the exterior unit depends on various factors such as the distance to the interior unit, level ground, proximity to windows or doors, and code-required distances from gas or water meters.

  • Connect the line set: A pair of copper pipes connects the two halves of the split system, allowing the refrigerant to cycle through. The route of the line set will be determined by the most direct path from the evaporator to the condenser.

  • Connect the electrical supply: An exterior shutoff is installed for the condenser unit, and the electrical line is connected from the condenser to the shutoff and from the shutoff to the electrical service panel. If necessary, the circuit panel may need to be upgraded to accommodate the additional load.

  • Condensate drain line: All air conditioners generate condensation that needs to be drained. The drainage method varies based on the unit's location, either running to a floor drain or using a drain pan in attics.

  • Thermostat: If you're installing central air conditioning in a new build, choose a thermostat. For existing homes, you may need to upgrade the thermostat to one that can control cooling. This is an opportunity for a DIY effort, where you can start with a basic thermostat and later upgrade to a programmable or smart thermostat.

How Much Does Central Air Installation Cost?

The cost of central air installation varies depending on factors such as the local market and job specifications. For labor and materials, a typical split system central air installation using an existing furnace should cost between $3,000 and $5,500. The majority of the cost is usually allocated to labor. If you choose to purchase the AC system independently and hire an HVAC professional for installation, keep in mind that you may pay full retail price and bear responsibility for any equipment issues. Additionally, removing and disposing of an old system may incur an additional charge.


Installing central air conditioning is a worthwhile investment that enhances the value of your home and provides a comfortable environment for you and your family. Although it's a complex installation, understanding the process and working closely with professional HVAC installers will ensure a smooth experience. Don't hesitate to ask questions and seek clarification throughout the installation process.

By following this guide, you'll be well-prepared to make informed decisions and enjoy the benefits of a properly installed central air conditioning system.