Central AC

Central air conditioning unit options – should you buy a single-stage, two-stage or variable speed?

If you’re considering replacing your central AC unit, the terms single-stage, two-stage and variable-speed are going to come up in your online searches and conversations with contractors. To make the right decision about which central air conditioner is right for you, it’s important to understand how each of these options will impact your comfort and budget.

All of these terms refer to the speeds – or speed, in one case – at which a central air conditioning system’s compressor can operate.

  • A single-stage central AC system is either on – full blast – or off. There’s no in between. This results in wasted energy and money. Imagine you’re driving, and your only means of maintaining the speed limit is to floor it or take your foot off the gas pedal. That’s single-stage technology.

    This is not to say a single-stage system is never the right choice. It is the least expensive type of central air conditioning system to purchase, so if upfront cost is a more important factor to you than long-term operating costs and performance, it may be the right solution. However, if energy- and cost-efficiency are important to you, a two- or variable-speed unit is likely a better fit.

  • A two-stage central air conditioner has two levels of operation: low (approximately 70% of capacity) and high (100% of capacity). Most two-stage systems can meet cooling demands operating at the lower speed 80% of the time – even in Austin, Texas. This equates to significant savings over a single-stage system.
  • A variable-speed central AC unit can operate at any percentage of its capacity, which means it only utilizes the energy necessary to meet cooling demands. Back to our driving example. The variable-speed scenario is more like using cruise control (we’re hypothesizing here, so there’s no Austin traffic to prevent us from doing this). You set it to the speed limit (temperature) you want, and it maintains it by adjusting its energy usage to the environment. You go up a hill (higher outside temperature), and it uses more power. You go down a hill (lower outside temperature), and it uses less. The ability to tailor output to demand makes variable-speed units the most efficient and cost-effective to operate.

Benefits of two- and variable-speed central air conditioners

A single-stage system cycles on and off more frequently, while a two- or variable-speed central AC unit runs for longer at lower speeds – cycling on and off much less often. In addition to the energy and cost savings discussed above, this offers important advantages:

  • More consistent comfort: Frequent on/off cycling means greater temperature swings. When a single-stage system kicks on, it often chills occupants with blasts of cold air. When it reaches the desired temperature, it shuts off, and the indoor environment grows increasingly warm and stuffy until the system delivers its next blast. By operating more continuously, a two-stage or variable-speed central AC unit is able to maintain the desired temperature with less variation.
  • Less wear and tear: Cycling on and off not only uses more power, it also puts your central air conditioner under more stress. Less wear and tear can mean lower maintenance costs and longer lifespan, especially when coupled with proactive maintenance service.

We are experienced with repair and installation of all of these system types and can help you weigh your options. We provide service and complimentary in-home AC replacement consultations all over the Austin area – from Kyle to Georgetown. Call us at 512-501-2275 to schedule.