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Difference Between Single-Stage, Two-Stage & Variable-Speed HVAC

by vscontent on September 8, 2017

HVAC technology is constantly improving to use less energy and deliver better performance. One of the best technologies available today is a Variable Speed.

When you start researching central air conditioning systems, you’ve undoubtedly come across variable-speed options, along with terms such as single-stage and two-stage compressors. These normally refer to variable-speed compressors and matching variable-speed indoor air handlers (blower coil or furnace).

So, what exactly is a Variable Speed Air Handle or Compressor and how is it different from single-stage or two-stage/multi-stage HVAC design?

Variable-Speed HVAC Technology

Variable-speed options are taking over the HVAC industry. Nearly all heating and cooling systems now come with variable-speed technologies.

A variable-speed compressor is also known as an inverter-driven or inverter compressor. It allows the HVAC system to use only the amount of energy needed to deliver the cooling capacity that you need.

For instance, if it is 90 degrees outside, the air conditioner may need to run at near full capacity to handle the load, but when it is only 80 degrees, the load is lower, so the speed can change (hence variable speed). By only using the amount of power and energy you need, you’ll consume less energy, which saves money and helps Mother Earth at the same time.

Energy Efficiency:

In essence, variable speed compressors and air handlers save you money and energy by tailoring the electrical consumption to the need. Variable-speed motors are energy-efficient and excellent for zoning, which allows you to customize thermostat settings for different areas of the home.


Besides savings, the other benefit of a variable speed compressor is that you won’t feel uncomfortable blasts of hot or cold air when the system comes on. Instead, the amount of conditioned air that enters your home comes in incremental doses.

Air Quality and Humidity Control:

Variable-speed heating and cooling usually runs for longer periods of time, but at a lower setting. Less energy and force means quieter operation and a better airflow. It’s cheaper to keep the system on at low levels than turning it on and off more frequently.

The longer, better airflow cycles also improve humidification levels, air filtration, and decrease the chances of duct leaks and comfort problems.

There are a few things to keep in mind when deciding on owning a variable-speed HVAC systems. Since the parts are highly complex, repairs will be more expensive.

Two-Stage and Multi-Stage HVAC

If you don’t know the difference between variable-speed and multi-stage, you’re not alone. Although they are similar, variable speed systems speed up or slow down as needed. Multi-stage technology, which are normally just two stages, shift back and forth between a one high speed and one low speed.

True variable-speed units fully adjust to the needs of the home whereas multi-stage motors switch between different fixed-speed settings.

When needed, a two-stage unit will run at full capacity. Most of the time, however, it will run at its slower speed, around ¾ capacity.

Single-Stage HVAC

When you have a single stage/speed system, your heat pump or furnace will run at one speed the entire year. This can be very inefficient, especially if you live in a moderate climate where the single speed can be consuming a lot more energy than needed.

A single-speed AC system will most likely be oversized, whereas a variable speed system will be able to change based on the demands of the home. Of your three speed options, single stage systems are the least efficient.

Installation and Lifetime Costs

In order to make a wise decision about upgrading and replacing your air conditioning and/or heating system  system, it’s a good idea to calculate first-time and lifetime costs of a replacement. The one-time costs of replacing your AC system include purchase and installation costs, along with any relevant fees, add-ons, and rebates. Lifetime costs take into account monthly operating costs, repairs, supplies, and preventative maintenance.

Contact Pacific Heating & Cooling to speak with one of our professional Comfort Advisors to weigh your options.

Since 1984, we’ve been proudly serving our communities in Pierce, S. King, and N. Thurston County.

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