What is a Two-Stage Air Conditioner or Heat Pump?

Two Stage Cooling Energy Efficient Feature

If you are researching a new air conditioner or heat pump, you may notice a few features that didn’t exist a few years ago. One of those is two-stage cooling, and its demand by homeowners is rising!

Two-stage cooling refers to the type of compressor that’s in the outside condensing unit. This feature allows for two levels of operation depending on your cooling needs — full capacity on hot summer days or part capacity for milder days. It is a great energy-efficient option when compared to a traditional, single-stage unit.

It’s All About Demand!

When you “start” a bicycle with your feet on the pedals, you have to put in a lot of initial effort to get up to speed.  You may even have to stand up to get the pedals going! The same idea can be applied to an air conditioner or heat pump turning ON at 100% capacity. A single-stage unit cools at 100% capacity until it reaches your preset indoor temperature and then turns off.

Think again about riding your bike. It takes less energy to maintain a comfortable biking speed than it does to get up to speed. The same concept applies to two-stage cooling. A two-stage heat pump or air conditioner may use 100% full capacity to reach your desired interior temperature, but then it may use part-capacity to maintain your setting as long as possible.

Depending on the outdoor temperature and the energy-efficiency and insulating variables of your home, your two-stage air conditioner or heat pump may have to remain at 100% to maintain that preset indoor temperature. This is similar to riding your bicycle uphill — you can’t back off your pedaling efforts or you may get pulled down the hill. Just like the heat, the opposing force is too great so you have to keep up your power in order to reach your goal!

For example, if the outdoor temperature is 95°F and the thermostat or control system is set at 75°F, your system might stay at 100% capacity to reach and sustain 75°F. But if the outdoor temperature is only moderately warm, a two-stage system may be able to operate with less capacity to maintain the preset indoor temperature. Depending on your home’s energy-efficiency variables, the limited cooling demand may result in nearly a 35% speed reduction at both the compressor and indoor unit circulating fan compared to a single-stage heat pump or air conditioner.

Benefits of Two-Stage Cooling


The two-stage unit may seem to run longer than a traditional single-stage unit, but this part-capacity operation offers energy-saving benefits that you will feel throughout your home:

  • Consistent Indoor Comfort – With its ability to adjust cooling output, your two-stage air conditioner or heat pump may minimize the peaks and valleys of cooling often found with the ON/OFF cycle of a single-stage unit. The lower stage capacity is able to maintain the pre-set temperature longer than if the system turns off when it reaches the pre-set temperature. This allows for steady cooling comfort in your home.
  • Dehumidification - The extended operation of a two-stage air conditioner or heat pump runs longer which removes more moisture from the interior spaces structure.  While the main job of the air conditioner or heat pump is to condition the air to a set temperature, these comfort-creating pieces of equipment may lower the indoor humidity level as a by-product of the cooling process.  Better humidity control leaves you with more comfortable interior air. When humidity levels are better controlled, you may be able to increase the set temperature on your thermostat or control system and still be comfortable in your home.
  • Energy-Efficient – You may think that because a two-stage cooling unit operates longer than a single-stage unit that it would use more electricity, but electricity usage peaks when a system turns ON. The two-stage feature actually reduces the peak start/stop load cycle which reduces the draw on your electricity. The capacity of the air conditioner or heat pump compressor changes to meet the cooling demand and therefore reduces energy consumption.


While full cooling capacity provides indoor comfort on the hottest days of the year, the extended operation at the part capacity helps maintain the indoor temperature for a longer period of time and dehumidifies the conditioned air in the process. With two-stage cooling, your air conditioner or heat pump may help you enjoy steady and consistent cooling when compared to the single-speed unit.

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