What is a Two-Stage HVAC System?

By Anne Fonda

In HVAC equipment, the word stages refers to the heating or cooling capability. The stage may also be referred to as speed - as in single-speed, two-speed, and variable-speed. Two stages simply means the unit has two heating stages or two cooling stages. Low speed, or first stage, might be running at 65% capacity, while the second stage, or second speed would be at 100% capacity.

Your thermostat and the outdoor temperature will determine which level of operation the unit runs at. For example on a bitterly cold winter day, the two-stage furnace would run at 100% capacity to keep your home warm. But on a milder winter day, it might run at 65% for most of the day.

Your two-stage AC or heat pump would do the same thing - on a 95+ degree day, it would spend most of its time running in the second stage, at 100% capacity. As nighttime temperatures fall, the unit would enter low speed and run at 65% capacity.

Two-stage heating and cooling can involve a paired two-stage furnace with a two-stage heat pump or two-stage AC unit. Some packaged systems also offer two-stage heating and cooling. 

A two-stage system is more efficient at heating and cooling your home when compared with a comparable traditional single-stage unit. It is also more effective at keeping an even temperature throughout your home.

A single-stage furnace, AC, or heat pump has one speed, so it’s either operating at 100% capacity or it’s off. It runs until it reaches the set temperature on your thermostat, and then shuts off. It turns on again when the temperature rises or falls a few degrees.

Two-stage systems may last longer than a single-stage system because they’re not starting and stopping as often as a single-stage unit. That means less stress on the system. But that’s not a guarantee. A well-maintained single-stage system could last longer. 

Single-stage systems are the base units in a line of furnaces, air conditioners, or heat pumps. 

This makes them the least expensive to purchase. Conversely, because they operate at 100% full capacity all the time, single-stage systems can be the most expensive to operate.

A third option for AC units, heat pumps, and furnaces is a variable-speed system. It’s the most energy-efficient type of system, but also more expensive upfront. In American Standard units, the variable speed system has more than 700 speeds to offer you optimal indoor temperature and humidity control, even on the hottest days.

Variable-speed systems can run anywhere from 25% to 100% capacity to offer you precise heating and cooling while saving energy. These systems may run for longer periods but use less energy.

Need more information on single-stage vs two-stage heating and cooling vs a variable speed system? Contact your local American Standard dealer for expert product recommendations tailored to your home.

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need. 

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Mark Woodruff, Senior Product Manager, Ducted Outdoor