In recent years, two-stage air conditioners have gained significantly in popularity with homeowners. Their flexibility, energy efficiency, and more consistent cooling power are all pluses. At the same time, there are drawbacks to these popular units you’ll want to know about before deciding to buy a new unit.
Single-Stage vs. Two-Stage Air Conditioners
To understand the unique downsides that two-stage ACs can have, it helps to understand the difference between how single-stage and two-stage ACs work. First, the terms “single-stage” and “two-stage” refer to the working capacity of the AC’s compressor.
A single-stage AC has a single compressor speed – it’s either on or off, in the manner of a traditional light switch. When ON, your AC will blow cold air at top capacity (100%) until it reaches the set temperature. Then it will shut OFF and repeat the cycle when the temperature increases. That repeated cycling can be frequent, resulting in more wear and tear on the motor and often leading to uneven temperatures – and possibly higher energy bills.
A two-stage AC has two speeds. ON typically runs at 100% capacity and LOW is usually around 60-70% capacity. Typically the AC will run at the lower setting much of the time. But on high heat days, it can kick into the higher speed. That means the cooling cycles will be longer, but it also cuts down on energy-draining starts and stops, reducing energy costs and wear and tear on the motor in the long run.
Common Drawbacks to Two-Stage ACs
While they’re more flexible and can save on energy, two-stage ACs can have their own downsides. First, they cost more than single-stage units. That may make them less attractive for smaller homes or milder climates where the cooling needs are moderate.
Because their technology is more complex, two-stage systems can also be more expensive to repair if something goes wrong. Both parts and labor costs are typically higher than a single-stage unit. And depending on where you live, you may not find as many qualified HVAC pros who have experience with the more complex two-stage systems to choose from.
Finally, two-stage energy efficiency, while typically better than a single-stage unit, may not perform as well as advertised. The efficiency rating for an AC is measured as a SEER value – the higher the SEER, the greater the unit’s efficiency. However, in actual practice, that efficiency can be lower than advertised. It’s not that anyone’s trying to mislead you. It’s simply that any system will perform differently under different circumstances. Tests have shown that two-stage ACs can perform significantly lower than their advertised SEER when installed in leaky homes, homes with oversized cooling systems, and when the fan is allowed to run even when the AC isn’t on.
Despite these drawbacks, two-stage ACs are an excellent choice for many homeowners. But they’re not the only alternative to a single-stage unit.
An alternative to both single-stage and two-stage ACs is a variable-speed unit. This AC’s compressor can vary its output from 0-100%, depending on your home’s cooling needs. For example, if you just need a few degrees of cooling, the AC can run at something like 30% capacity. But if you’ve come home to a hot, stuffy house and need to quickly cool down by 10 or 15 degrees, the compressor will run closer to 90% capacity to reach your target temperature.
In addition to increased flexibility, variable-speed ACs offer top efficiency, steadier temperatures, and even better humidity control. If you’re wondering if a new two-stage AC is right for you, be sure to check out the advantages of a variable-speed unit as well. You just might find it’s the ideal solution for your home.
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