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 HVAC 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.
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. 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.
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 AC 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.
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:
In summary, careful consideration of needs, wants and budget will help you make the best selection. If the unit is for your primary residence, and you plan to stay for a while, consider the options that will make a difference for you. Most of our customers, once they experience the better two-stage or variable systems, never go back. Similar to buying a new car, spending more does get more. Unlike the typical car, spending more also gets better efficiency and at least a partial financial return – if not full – on the added upfront cost.
At Efficient AC, Electrical & Plumbing, we are experienced with repair and installation of all of these system types and can help you weigh your options. We have provided professional AC services and complimentary in-home AC replacement consultations all over the Austin area – from Kyle to Georgetown — since 1976. Call us at 512-501-2275 to schedule.