Man confused by different types of AC units to choose from

June 2024
By: Josh Walejewski
Read Time: 3-4 Minutes

Imagine this…

You walk through your front door after a long day at work, eager to escape the scorching summer heat. Instead, you’re met with a wave of hot, humid air. Did you forget to turn on the air conditioning? You rush over to the thermostat, puzzled. It’s set to 71 degrees, but the display reads a sweltering 79. Oh no! Your old AC must have finally given out.

Your faithful air conditioner has been a trooper, keeping you cool for over 20 years. But now, during the hottest times of the year, it’s decided to retire. Frustrated and sweaty, you pick up the phone to call your HVAC service provider, hoping they can save you from this heatwave.

A friendly representative arrives promptly, assesses your situation, and presents you with several options for a replacement. Single-stage, two-stage, variable-speed… your head starts to spin with the jargon. What do these terms even mean?

In today’s blog, we’ll give you the lowdown on the differences between single-stage, two-stage, and variable-speed air conditioners. This way, if you actually find yourself this situation, you can be sure to make the best decision for your comfort needs.
How does single stage, two-stage, and variable speed work?

How Single-Stage ACs Work

You can think of single-stage ACs like a light switch. They are either 100% ON or OFF. When the thermostat detects that the temperature has risen above the desired setting, the AC turns on at full capacity until the target temperature is reached. Then, it shuts off completely until it’s needed again.

Pros of Single-Stage ACs

Considerations for Single-Stage ACs

How Two-Stage ACs Work

Two-stage air conditioners offer a more versatile approach to cooling. As the name suggests, they have two levels of operation: A lower speed and a high speed. The lower setting/speed (usually 70% capacity) is used the majority of the time when cooling demands are average. When temperature and cooling demand are higher, it runs at 100% output.

While it may sound counterintuitive, two-stage air conditioners are far more efficient and keep your home comfortable throughout than single-stage units because they run longer. Think of it like driving a car. If you’re constantly starting and stopping in city traffic, your car uses more fuel. But if you’re cruising smoothly on the highway, you use less fuel overall, even though you’re driving for a longer distance.

This longer, more consistent operation not only keeps your home at a more even temperature but also reduces energy consumption and wear on the system.

Pros of Two-Stage ACs

Considerations for Two-Stage ACs

Lennox Variable Capacity AC

How Variable-Speed ACs Work

Variable-speed air conditioners, also referred to as modulating or variable-capacity air conditioners, represent the pinnacle of cooling technology. These systems can adjust their output between 35% and 100%, providing precise temperature control.

For instance, the Lennox the SL28XCV air conditioner has 65 stages of cooling.Its innovative compressor technology can adjust its output in increments as small as 1%. They operate continuously at varying speeds to match the exact cooling demand at any given time.

With precise control, these units are designed to keep indoor air within .5 degrees of the desired temperature.

Pros of Variable-Speed ACs

Considerations for Variable-Speed ACs

Do Variable-Speed ACs / Heat Pumps Work with All Furnaces?

If you’re considering upgrading to a variable-speed air conditioner, it’s important to know that your existing furnace or air handling is compatible. Here’s why:

To reap the benefits a variable speed AC brings, it also relies on the ability to adjust airflow in tandem with cooling output. A variable-speed furnace or air handler has a blower motor that can adjust its speed to match the cooling output of the variable-speed AC.

If your existing furnace or air handler only has a single or two-stage blower motor, it won’t be able to modulate airflow in sync with the variable-speed cooling output of the AC. If you are thinking about variable-speed AC, a comfort specialist will be able to ensure that your existing equipment is compatible.

What Role Does Humidity Play in Our Home’s Comfort?

Ever heard the phrase “it’s not the heat it’s the humidity”? Humidity significantly impacts indoor comfort during the summer. High humidity levels can make the air feel warmer than it actually is, leading to discomfort. Air conditioners help manage humidity by removing moisture as they cool your home.


Choosing the right air conditioner for your home can seem overwhelming, but understanding the differences between single-stage, two-stage, and variable-speed units can help you make an informed decision. Each type has its advantages and considerations, and the best choice depends on your specific needs.

Whether you prioritize cost, comfort, energy efficiency, or all of the above, our team can help you find an AC system that’s perfect for you and your home. Contact us today.

Read more blog posts from Kettle Moraine Heating & AC.

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About the Author
Josh Walejewski

Josh is a professional marketer who has worked in the HVAC industry since 2017. With a Bachelor of Applied Arts and Sciences Degree (B.A.A.S) in marketing and sustainable business management from the University of Wisconsin, he has a passion for all aspects of HVAC, business, marketing, and environmental stewardship.


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