Informational Guide

Single Stage Vs Two Stage AC Units

Selecting a single-stage, dual-stage, or variable speed air conditioner depends on the room size, the cooling time needed, and how long you expect it to last.

by Ian Haynes

Finding the most efficient cooling option for your room can be a tiresome process; there are just too many options.

This becomes even more confusing when buying a permanent HVAC system such as a central air conditioner, partly because you have to choose between single-stage vs. two-stage air conditioner compressors.

A single-stage system’s compressor has one power setting, and that is to function at maximum cooling capacity. The air present is stored in the storage container through a single piston stroke.

Benefits
  • Quite commonly used and easy to install
  • Comparatively easier to repair
  • Provides efficient cooling if placed adequately
  • Comparatively less expensive
Negatives
  • Use more energy since they always run at maximum capacity
  • Experience more wear and tear due to continuous operations
  • Provides comparatively uneven cooling

Pros & Cons Of Two-Stage Air Conditioners

Two-stage air conditioners allow air to be compressed in a single chamber. It is then transferred to a second chamber, where it is compressed again.

This efficiently provides two different speeds to control AC output according to the required cooling.

Benefits
  • Dual cooling capacity — full blast on hot days and low cooling on colder days
  • Low noise and relatively quieter
  • Even cooling throughout the house
  • Dehumidifies the house effectively
Negatives
  • Initially expensive
  • Higher maintenance and difficult to repair

Single Vs Two-Stage Air Conditioners Compared

When comparing single & two-stage air conditioners, we have to consider their differing compressor speeds. Single-stage units have a single compressor speed, so they function at either 100% or not at all.

In contrast, two-stage compressor systems have two compressor speeds, with one generally set to 60-70 percent of maximum efficiency. Therefore, for the most part, they run at moderate speeds. However, on hotter days, a two-stage compressor shifts to a higher speed setting.

Split Air Conditioner on House Roof

Cost

When measuring and comparing the costs related to 1 stage vs. 2 stage AC units, the latter comes out on top, or bottom, depending on how you see it.

They are priced higher than the single-stage models because of the complex technology that goes into their production.

This additional cost can make it hard to justify buying a two-stage air conditioning system in milder climates or smaller houses. However, they provide more internal temperature control.

Maintenance

A typical single-stage air conditioner relies on one compressor speed; thus, repairing and maintaining it is more straightforward. Their replacement parts are also easier to find.

However, the two-stage units employ newer technology; they also have a higher number of components; therefore, maintaining or repairing them can be challenging.

Furthermore, not every technician is trained or equipped to deal with this advanced technology. And more often than not, maintenance specialists may lack access to replacement parts for these ACs.

Efficiency

The seasonal energy efficiency ratio (SEER) is an indicator of how efficient an AC unit is. The higher the values, the more efficient the system. Generally, single-stage air conditioning units have lower SEER values than two-stage ones.

A typical single-stage unit only functions at maximum capacity. When the temperature falls below the setting on the thermostat, the cycle starts again. This constant process of starting and restarting reduces the efficiency of the system significantly.

On the other hand, two-stage air conditioners cool your house at a lower speed for a longer duration. Following this pattern allows the unit to provide consistent cooling alongside being increasing its life expectancy.

Installation

When discussing the comparative installation costs of single-stage vs. double-stage air conditioners, the former takes a slight advantage over the more advanced model as its upfront costs are lower.

Nonetheless, a single-stage air conditioning system ends up costing more in terms of aftersale maintenance and use-based repairs.

However, if you lack the immediate capital limit to purchase a two-stage unit, a single-stage air conditioning system is your best bet. Albeit, its installation process is more straightforward.

Comfort

The difference in cooling cycles of single-stage vs. double-stage air conditioners also directly affects performance.

Since single-stage systems go through frequent cooling cycles, they can cause significant temperature fluctuations throughout the day.

Additionally, their shorter cooling cycles prevent efficient dehumidifying. Whereas double-stage air conditioner cooling cycles are less stressful on the system and longer-lasting, thus cooling your house gradually and dehumidifying effectively.

Comparing Single and Two-Stage to Variable Speed ACs

When thinking of getting a new air conditioner, the buck doesn’t stop with the two stages. You must also consider single-stage vs. two-stage vs variable speed AC. The latest entrant in the discussion, the variable speed air conditioning system, can effectively run at multiple speeds.

Air Quality

When a system runs for a longer time, the indoor air quality significantly increases. This is because the lower the air conditioner’s speed, the longer it will run. Thus a variable speed AC will continuously cycle air and clean it every time.

In comparison, the double-stage system will cycle air longer than the single-stage but not as effective as the variable speed unit.

Comfort Level

Variable-speed and two-stage air conditioners will provide more control over your home’s temperature levels than single-stage units. Both two-stage and variable speed ACs can function at lower speeds, allowing minor adjustments to the temperatures.

However, with a single-stage unit, you can achieve your desired comfort level, but you cannot fine-tune your temperature levels like the other option.

Noise Levels

At slower speeds, air conditioners are relatively quiet. However, considering single-stage vs variable speed AC and two-stage, all three can function at higher speeds. But still, single-stage ones are as loud as 76 decibels.

Conversely, a double-stage system can go as low as 67 decibels, whereas the variable speed system can operate at approximately 55 decibels.

Humidity

Just like the air quality, your air conditioner can also manage humidity. The higher air cycles a system has, the lower its humidity. This is because cool air cannot hold water like warm air; when warm air goes through evaporator coils, the moisture inside is deposited and cooled.

As a result, variable speed air conditioners are an excellent option for reducing humidity; whereas, the single-stage unit can only remove water in small bursts while running at maximum capacity.

Energy Efficiency

Variable-speed air conditioners provide the highest energy efficiency amongst all other options. Even though they function harder, they do so at lower speeds, making them very efficient.

Additionally, more energy is consumed by cycling on and off; therefore, single-stage systems consume more energy during their operation and cycling.

Typically, the SEER rating of single-stage air conditioners is around 18.5 or lower. On the other hand, two-stage units can have ratings as high as 21, whereas variable speed systems offer a SEER rating of 26.

Heat Pump on Roof

People Also Ask (FAQ)

Can I Use A Two-Stage AC With A Single-Stage Furnace?

No, you cannot. A two-stage air conditioner requires a two-stage furnace, and even though you might be able to circumvent it by employing an experimental technician, it will not run for long.

How Do I Know If My Compressor Is 2 Stages?

The most evident difference between a single-stage and dual-stage compressor is the cylinder’s shape; this is also where the pistons are located.

In a single-stage pump, both cylinders and pistons are of the same dimension and size. In comparison, a 2-stage pump has a low-pressure piston alongside a smaller high-pressure piston.

How Much Money Does A Variable Speed Blower Save?

The blower motor of a variable-speed air conditioner adjusts the way your system cools your house, thus reducing the monthly energy costs. A variable-speed blower motor can save as much as 400 USD a year.

What Is The Difference Between Multi-Speed And Variable Speed?

A multi-speed air conditioner will continue working at the same speed and temperature even when the room is cold. In contrast, variable speed air conditioners adjust according to the environment.

Conclusion

The choice of an air conditioner depends on multiple factors. Selecting a single-stage, dual-stage, or variable speed air conditioning unit depends on the room you want to cool, the number of hours in the day you require cooling, and how long you expect it to last.

Ian Haynes

Ian Haynes is an HVAC writer, and researcher. He has worked on hundreds of articles relating to home cooling, heating and air quality with a vast knowledge of the technical aspects of these types of appliances. Outside of his work, Ian likes exploring Brooklyn with his Labrador. Learn more about the AC Lab team here.

Top