Contents (Click To Jump)
How Do Variable Speed Air Conditioners Work?
Almost all HVAC professionals will agree that variable-speed air conditioners are the most efficient type of AC unit around. Compared to single-stage and two-stage AC units, they use less energy and provide a better comfort level in your home.
Variable-speed refers to the amount of cooling the compressor in your air conditioner can provide. Variable means it can throttle the amount of refrigerant cooling from 1 to 100% (full capacity), usually in 1% increments (depending on the model).
So, if it is a scorching day, your AC unit may provide close to 100% cooling output from the compressor. However, it may only run at 30% to 40% during a mild spring day with a lower temperature.
A variable-speed system blows a steady stream of cool air into your home for long periods before turning off. The almost constant supply of air balances the temperature in your home, which reduces hot spots and cold spots.
Their longer run time also means variable-speed AC units have time for dehumidification, further improving your indoor comfort. This is particularly useful for those that live in humid climates and struggle with high levels of indoor relative humidity (RH).
How Do Variable-Speed ACs Compare To Other AC Types?
Variable-speed air conditioners keep the indoor air temperature and humidity of your home more steady and comfortable. If you’re considering a variable speed air conditioner, you should first compare it to other types of AC units like single-stage and two-stage units.
Variable speed usually refers to the compressor but can refer to the blower motor as well. For example, an air conditioner may have a variable-speed compressor, a variable-speed fan, or both. The manufacturer or HVAC dealer usually differentiates this by stating “variable speed compressor” or “variable speed fan.”
On the other hand, two-stage and single-stage only refer to the type of compressor inside the air conditioner. Blower motors always go by “single-speed” and “multi-speed.”
Here’s how variable-speed, single-stage, and two-stage AC units stack up.
Variable Speed Vs. Single-Stage
Single-stage air conditioners have just two settings, on and off. This means when your air conditioner runs, it stays on at 100% every time. As such, your home will experience temperature fluctuations.
For example, let’s say your thermostat’s setpoint is 70ºF. When your indoor air temperature gets a few degrees above 70ºF- the single-stage AC unit will trip on and run full-blast until the thermostat measures a temperature lower than 70ºF. This is how it should work in theory.
However, it does not.
The indoor air temperature can fluctuate three to five degrees above or below the thermostat’s setpoint with a single-stage system. This can also create an uneven temperature in your home. To elaborate, it could make the temperature upstairs multiple degrees warmer than the temperature near the thermostat.
Therefore with a single-stage air conditioner, your indoor air temperature tends to bounce around as much as 5 degrees below or above your thermostat’s setpoint. Plus, you can have hotspots and cold spots along with high indoor relative humidity.
Variable Speed Vs. Two-Stage
Two-stage air conditioners improve upon single-stage AC units by providing an additional setting. Instead of just “on” and “off,” two-stage units have 40% and 100% output stages.
You can think of these as a “low” and “high” setting. Two-stage units often use the “low” mode and run for more extended periods, which is more efficient.
On the other hand, a two-stage AC unit will only throttle to the “high” mode, or 100% capacity, if there’s a large temperature differential between the thermostat’s setting and the indoor temperature. Since they run longer and at lower settings, two-stage units provide better temperature and humidity control and improve energy usage over their single-stage siblings.
Variable-speed AC units provide the best control of humidity and temperature and are the most efficient. Compared to the peaks and valleys that single-stage and two-stage air conditioners offer, a variable speed unit holds the temperature in a straight line. Here’s how all three stack up:
|Air Conditioner Stages||Single-Stage||Two-Stage||Variable-Speed|
|Cooling output||Off or 100%||Off, 40%, or 100%||0-100% in 1% increments|
|Efficiency||Lower Efficiency||Better Efficiency||Best Efficiency|
|Temperature Control||Good, some hot/cold spots possible with temperature fluctuations||Better, minimal temperature difference with fewer fluctuations||Best, stead with +/-1ºF for most homes|
|Humidity Control||Sufficient besides in humid areas||Good humidity control||Best performance reducing humidity|
What Are The Advantages of Variable Speed ACs?
Variable-speed air conditioners provide top-of-the-line performance that makes them a fantastic machine for most homes. Here are the main advantages of variable-speed air conditioning units.
Have you ever been inside a home and felt too cold only to become too hot all within the span of a half-hour? Well, you’re not alone.
That is a common side-effect of how single-stage air conditioners cool homes. In other words, the single-stage AC unit overshoots the thermostat’s setpoint and cools it too much. Then, it turns off, and the indoor temperature may drop below to setpoint momentarily before repeating this cycle.
This isn’t the case for all homes with single-stage air conditioners, and sometimes it is enough to notice, but it is common.
On the flipside, variable-speed air conditioners keep the indoor temperature bullseye on your thermostat’s setpoint. Plus, there will be fewer hot spots and cold spots in your home since the AC runs lower and longer, allowing the temperature in your home to equalize.
Lastly, variable-speed AC units remove more humidity, again due to the simple fact that they run longer and more often. This not only makes them more energy-efficient, but it gives the AC unit more time and additional air changes to remove more moisture.
Typically, variable-speed AC units will run at 40-50% output the majority of the time. However, they may kick on at 100% before ramping down to a lower setting when they first start.
When the compressor runs at lower speeds, it’s quieter, which is less intrusive to some homeowners. On the other hand, some homeowners tune out the air conditioner no matter how loud it gets.
Lowers Cooling Bills
Variable-speed AC units are more efficient, which means they will use less energy to keep your home cool than a single-stage or two-stage AC unit. Your utility bills will be lower, and over the typical 15 to 25-year lifespan of a typical air conditioner, you could save thousands of dollars in electricity costs.
May Qualify for Rebates
Certain states and utility companies may offer rebates if you purchase an air conditioner with a high-efficiency rating. Since variable-speed air conditioners have some of the best SEER (Seasonal Energy Efficiency Ratio) ratings on the market, they usually qualify for these rebates.
Rebates are constantly changing, so it is best to check with your state, county, and utility company to determine if they offer any rebates and what AC systems qualify.
What Are The Disadvantages of Variable Speed ACs?
Although variable-speed AC units are highly efficient and fantastic in their own right, they have their downsides. Depending on your home and specific situation, you might be better off with a single-stage or two-stage air conditioner. Here are the main disadvantages of variable-speed air conditioning systems.
Higher Upfront Cost
Variable-speed air conditioners are generally the “flagship” models of an air conditioner’s manufacturer’s lineup. As such, you will be paying a premium to get the best-in-class unit.
On average, variable speed AC units cost between $1,500 to $8,000 more than single-stage and two-stage air conditioners. Of course, the variable-speed unit is more efficient and therefore costs more.
Might be Overkill
Depending on the climate zone you live in, a variable speed air conditioner’s increased efficiency might not be worth the extra price. In some areas of the county where the summers are particularly mild with ideal relative humidity, a two-stage or even a single-stage AC unit might provide good performance.
In some of these instances, the energy savings a variable speed AC unit provides might be negligible. When in doubt if a variable speed unit is suitable for you, give our team of HVAC experts a call for recommendations.
Your Home May be Incompatible
If your home has a central air conditioning system in place already, replacing your old AC unit with a new variable speed one won’t be too much of a hassle. However, if you have uninsulated ducts, it could lead to the issue of condensation.
Since variable speed air conditioners run for so long, they keep your air ducts constantly cold. When bare metal ducts are cold for too long, your ductwork will start to sweat. In other words, condensation will form on the ductwork and drip into your walls, through your ceiling, or inside your floor.
This excessive moisture could lead to water damage (including wood rot) and mold or mildew growth. Homeowners with uninsulated ducts should consider single-stage and two-stage air conditioners to avoid this potential issue.
How Much Do The Variable Speed ACs Cost?
Variable-speed air conditioners cost between $4,000 to $8,000 on average for a completely new unit. Your cost will vary depending on the size of the AC unit (tonnage), the SEER rating, brand, model, blower type, and your locality.
Installation costs range from $2,000 to over $4,000, depending on the local rates and the complexity of the installation.
Are They Worth The Cost?
In most cases, variable-speed air conditioners are worth the cost. For example, let’s say you purchase a variable-speed AC unit for $2,000 more than a single-stage air conditioner. The variable-speed AC unit may use 15% less energy than the single-stage unit, meaning you also save 15% on your AC electricity cost.
So, if the electricity to run your variable-speed air conditioning unit costs $250 a month, it would have cost $287.50 per month with a single-stage unit. This $37.50 difference equates to a yearly savings of $450.
Therefore, you will break even on the upfront cost difference after about 4.5 years ($2,000/$450). If you live in the home longer than 4.5 years, getting a variable-speed AC unit is worth it (in this example).
This doesn’t even factor in your carbon footprint reduction and increased comfort, which might be worth more to you than money.
When Should You NOT Buy A Variable Speed AC?
While variable-speed air conditioners are excellent systems with high efficiencies, buying one doesn’t always make sense.
Here are some of the reasons you should take into consideration.
You Plan to Move Before Breaking Even
If you plan to move before you recoup your extra upfront cost through your reduction in energy bills, then buying a variable-speed HVAC system might not be a good idea. But, who knows? However unlikely, a variable-speed AC unit might get you a slightly better offer when you sell your home.
Condensation buildup on uninsulated metal ductwork is common when paired with a variable-speed AC unit. Insulating ductwork is usually cost prohibitive as you would have to remove drywall.
In this case, it might be better to purchase a two-stage AC unit instead to avoid potential water damage and mold problems.
You Live in a Mild Climate
As you’re contemplating whether or not you should get a variable-speed AC unit, ask yourself – how often do you use air conditioning? What are the summers like where you live? If your answers are “not often” and “pretty mild,” single-stage and two-stage are likely a better fit.
Your Energy Costs are Low
Perhaps you live in an area with extremely low-cost energy, or you might collect your own power with windmills and solar panels. Whatever the case, if your energy is cheap, it will be hard to recoup the extra upfront cost through electricity savings.