When you’re making a big purchase like a new air conditioner, it’s natural to look for ways to save money. Often, a smaller unit comes with a lower price tag, which can seem like a smart financial choice at first. However, that initial savings can quickly disappear. An undersized AC unit has to work overtime just to try and keep your home comfortable, causing a major spike in your monthly energy bills. This constant strain also leads to more frequent breakdowns and a shorter overall lifespan for the system. In the end, the “cheaper” option can cost you far more in the long run. Let’s explore why getting the right size is the best investment for your comfort and your wallet.
Undersized AC units are common in many homes. In some cases, it may be a financial choice because of the lower upfront costs with smaller models. Another reason is that household needs have changed, usually through renovations or by adding more members. Whatever the reason, an undersized AC unit can cause problems during the hot and humid Winston-Salem summers. Read on to learn how to size an AC unit to meet demand and find out some common signs that your unit may be too small for your home.
Could Your AC Be Undersized?
When your air conditioner first starts working during the hot summer months, all you care about is that you’re finally getting relief from the heat. However, over time, you may start to notice something isn’t quite right. Here are a few signs of an undersized AC unit.
Your house never reaches the desired temperature
If your home never cools to the desired temperature set on your thermostat, you likely have an undersized AC system. The outdoor temperature isn’t the only thing contributing to standing heat in your home. Furniture, people, and even walls can increase your home’s internal temperature. Cooling a home is easier and more efficient if the base temperature never varies more than five degrees from the set. An air conditioner takes one hour to decrease the temperature by one degree.
Uneven cooling and some rooms are always hot
Hot spots in your home indicate an inefficient and undersized system. In some cases, you can make adjustments by closing blinds and opening the vents in hot rooms and spaces. However, your system still needs to work extra hard to adequately regulate the temperature in your home.
Constant AC running without sufficient cooling
When your AC runs constantly but doesn’t cool, it’s a sign of an undersized system. A well-sized AC system should effectively cool your home without running nonstop, even on the hottest days.
Excessive Noise and Frequent Repairs
If your air conditioner sounds like it’s working overtime, it probably is. An undersized unit has to run almost constantly to keep up with your home’s cooling needs, putting a massive strain on its components. This relentless operation often results in loud, disruptive noises like buzzing, clanking, or groaning. A properly sized system should operate relatively quietly in the background. If your AC is making its presence known with a lot of noise, it’s a strong indicator that it’s struggling because it’s too small for the space.
That constant overexertion doesn’t just create noise—it also leads to premature wear and tear, resulting in more frequent breakdowns. You might find yourself scheduling more HVAC service calls for issues that shouldn’t be happening with a healthy system. The cost of these repeated repairs can add up quickly, and the ongoing stress can dramatically shorten your AC unit’s overall lifespan. If you’re dealing with a noisy, unreliable system, it’s worth having a professional evaluate whether your unit is the right size for your home.
Why Undersized ACs Cause Problems
So your AC is too small for your house — at least it offers some relief, right? Unfortunately, beyond poor cooling, an undersized AC causes other problems. When your AC isn’t cooling the whole house, humid spots may develop, which offer excellent breeding grounds for mold and mildew. Mold presents serious health concerns and potential remediation costs. You may incur high energy bills with an undersized AC system. A constantly running system uses more energy than a properly sized unit, which leads to excess wear and tear and frequent repair costs. The overcompensation and wear shorten the service life, meaning you’ll have to replace it sooner. In the end, the cheaper upfront cost of a smaller model can cost you more in day-to-day operation, repair costs, and early replacement.
Higher Energy Consumption
When an air conditioner is too small for the space it’s trying to cool, it has to run almost constantly to keep up. This continuous operation means the system never gets a break, especially on hot North Carolina days. According to HVAC experts, an undersized system “has to work much harder and run longer to try and keep your home comfortable, which uses more energy and costs you more money.” This constant strain translates directly into higher electricity bills. Instead of cycling on and off efficiently, your AC is in a perpetual state of catch-up, consuming a significant amount of power without ever achieving the desired result. It’s a frustrating cycle of paying more for less comfort.
Reduced Lifespan and System Strain
Think of your AC unit like any other machine; if you run it at maximum capacity all the time, it’s going to wear out faster. An undersized unit is always under immense strain, pushing its components like the compressor and fan motor to their limits. This relentless operation leads to premature wear and tear on critical parts. As one plumbing and repair service notes, “An undersized AC unit will break down much sooner because it works too hard.” Essentially, you’re shortening the functional lifespan of your investment. A properly sized unit might last 15-20 years, but an overworked, undersized one may fail much earlier, forcing you into a costly replacement you weren’t prepared for.
Increased Risk of Breakdowns
The constant stress on an undersized AC doesn’t just wear it out faster—it also makes it more prone to sudden breakdowns. When a system is always running, there’s no downtime for its components to cool off, leading to overheating and mechanical failures. This “constant strain from overworking can cause parts to break down more frequently,” leaving you without air conditioning when you need it most. Instead of enjoying a cool home, you could be facing emergency repair calls for issues that could have been avoided with a correctly sized system. These frequent repairs add up, turning a seemingly cheaper initial purchase into a long-term financial drain.
Refrigerant Leaks
One of the more serious consequences of an overworked AC is the potential for refrigerant leaks. The constant vibration and high pressure within a system that never stops running can cause cracks or weaknesses in the refrigerant lines. According to HVAC professionals, an undersized unit might even “leak harmful chemicals (refrigerant).” A refrigerant leak not only prevents your AC from cooling effectively but also poses an environmental and potential health risk. Repairing these leaks can be complex and expensive, often requiring a certified technician to handle the refrigerant safely and recharge the system.
Electrical Issues
The electrical components of your AC unit are also at risk when the system is undersized. The constant power draw can overheat wiring, damage capacitors, and wear out the compressor’s electrical connections. In a worst-case scenario, these “electrical problems… could lead to fires.” Frayed wires or failing components create a significant safety hazard. If you notice flickering lights when your AC kicks on or smell a burning odor near your unit, it’s a critical sign that the electrical load is too high, and you should have your system inspected immediately by a professional.
How to Properly Size an AC Unit
Figuring out the right size for your air conditioner is more of a science than a guessing game. It’s not as simple as picking the biggest unit you can afford or grabbing the same one your neighbor has. The goal is to find a system that is perfectly balanced for your home’s unique needs, ensuring it cools efficiently without wasting energy or wearing out prematurely. A correctly sized AC provides consistent comfort, better humidity control, and lower energy bills. It’s a crucial step that requires careful calculation and an understanding of how your home retains and loses heat. Getting this right from the start saves you from years of discomfort and unnecessary expenses.
Understanding Cooling Power: BTUs and Tons
When you look at air conditioners, you’ll see their cooling capacity measured in BTUs (British Thermal Units) or tons. A BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. In cooling terms, it’s the amount of heat an AC unit can remove from a room in one hour. One ton of cooling is equivalent to 12,000 BTUs per hour. While online calculators can give you a rough estimate based on your home’s square footage, they often miss the critical details that influence your actual cooling needs, like ceiling height, window quality, and insulation levels.
The Professional Method: Manual J Load Calculation
The industry standard for accurately sizing an HVAC system is a process called the Manual J load calculation. This isn’t a quick estimate; it’s a comprehensive analysis of your entire home. A certified technician will measure your home and factor in dozens of variables, including local climate, window size and type, insulation levels, air leakage, the number of occupants, and even heat-generating appliances. According to experts, a technician should perform an “‘ACCA Manual J load calculation’ [to] determine the correct HVAC size.” At QRC, our experienced technicians perform these detailed calculations to ensure we recommend a residential HVAC system that is perfectly tailored to your home, guaranteeing optimal performance and efficiency.
Is It Better to Undersize or Oversize an AC Unit?
It might seem logical to think that a bigger air conditioner will cool your home faster and better, but that’s a common and costly misconception. When it comes to HVAC systems, bigger is definitely not better. Both undersized and oversized units create significant problems, but in different ways. An undersized unit struggles to cool your home at all, while an oversized unit cools it too quickly, leading to a host of other issues. The ideal scenario is a “Goldilocks” fit—a system that is just right. A properly sized unit will run for consistent, long cycles, which allows it to cool your home evenly and effectively remove humidity from the air, all while operating at peak efficiency.
The Problems with an Oversized AC
An oversized air conditioner might sound like a luxury, but it functions more like a liability. These systems blast your home with cold air and then shut off abruptly, a process known as short cycling. This constant on-and-off jarring is incredibly inefficient and puts a lot of stress on the system’s components. Because it doesn’t run long enough, it fails to properly dehumidify the air, leaving your home feeling cool but clammy. This can lead to problems with mold and mildew growth. Ultimately, an oversized unit costs more to purchase, more to operate, and will likely need to be replaced sooner than a correctly sized one.
Short Cycling and Increased Wear and Tear
Short cycling is the number one problem with oversized AC units. The system uses a massive burst of energy to turn on, runs for just a few minutes to satisfy the thermostat, and then shuts off. This happens over and over again. This frequent starting and stopping puts excessive strain on the compressor, the heart of your AC system. As one source explains, a unit that is too big will “turn on and off too often… This can shorten its lifespan.” This repeated stress accelerates wear and tear on the most expensive component of your air conditioner, leading to premature failure and a costly replacement.
High Humidity and Poor Air Quality
A key function of your air conditioner is to remove moisture from the air as it cools. This process requires the system to run for a sustained period. Because oversized units cool the air so quickly and shut off, they “shut off before they can remove enough moisture from the air.” This leaves you with a room that feels cool but uncomfortably damp and sticky. High indoor humidity can lead to condensation on windows, a musty smell, and can even encourage the growth of mold and mildew, which can negatively impact your home’s air quality and your family’s health.
Wasted Energy and Higher Bills
You might think a system that runs for shorter periods would save energy, but the opposite is true for an oversized AC. The startup phase of an air conditioner’s cycle consumes the most electricity. Since an oversized unit is constantly starting and stopping, it never reaches its peak operational efficiency. As HVAC experts point out, “Bigger units use more power. They also don’t run long enough to become truly energy efficient, so they waste energy.” This inefficiency means you’re paying higher utility bills for a system that provides less comfort and poor humidity control.
Before You Replace: Other Causes of Poor Cooling
If your home isn’t staying cool, it’s easy to assume the AC unit itself is the problem. But before you start budgeting for a full system replacement, it’s important to investigate other potential culprits. Sometimes, an air conditioner that seems undersized is actually a perfectly capable unit that’s being held back by a different issue. Simple problems like a clogged filter or more complex ones like leaky ductwork can severely impact your system’s performance, mimicking the symptoms of an undersized unit. Taking the time to rule out these other possibilities can save you a lot of time, money, and stress. A thorough diagnosis is the first step toward finding the right solution.
Check for Common Issues First
Before calling for a major repair or replacement, there are a few simple things you can check yourself. These common issues are often overlooked but can have a huge impact on your AC’s ability to cool your home. Addressing them might be all you need to restore comfort and efficiency. Start with the easiest and most common problem: the air filter. From there, you can look for signs of other simple-to-spot issues. These preliminary checks can help you have a more informed conversation with an HVAC technician if you do need to make a service call.
Dirty Air Filters
A clogged air filter is one of the most frequent causes of poor cooling performance. The filter’s job is to trap dust, pollen, and other debris, but when it gets too full, it restricts airflow. This forces your AC’s blower motor to work harder to pull air through the system, reducing its efficiency and cooling power. It can even cause the evaporator coils to freeze over, stopping the cooling process entirely. Checking and changing your air filter regularly—typically every 1-3 months—is a simple, inexpensive maintenance task that can make a world of difference.
Low Refrigerant Levels
Refrigerant is the lifeblood of your air conditioning system; it’s the substance that absorbs heat from inside your home and releases it outside. If your system is low on refrigerant, it’s almost always because of a leak. A system with low refrigerant won’t be able to cool the air effectively, and you might notice symptoms like warm air blowing from the vents or ice forming on the refrigerant lines. This is not a DIY fix—handling refrigerant requires a certified technician who can find and repair the leak before safely recharging the system to the correct level.
Faulty Thermostats
Sometimes the problem isn’t with your AC unit at all, but with the device that controls it. A malfunctioning thermostat can send incorrect signals to your HVAC system, causing it to run improperly or not at all. It could be a simple issue like dead batteries, incorrect settings, or poor placement where it’s exposed to direct sunlight. If the thermostat’s sensor is faulty, it might not accurately read the room’s temperature, preventing the AC from turning on when it should. Upgrading to a modern, programmable or smart thermostat can also improve both comfort and efficiency.
The Importance of Ductwork
Your ductwork is the circulatory system for your home’s conditioned air, and its condition is just as important as the AC unit itself. If the ducts are leaky, blocked, or improperly sized, even the most powerful and efficient air conditioner won’t be able to cool your home effectively. The air will either escape into your attic or crawlspace or won’t be able to reach certain rooms at all. Many HVAC professionals believe that when a system is underperforming, the issue often lies with the ductwork, not the unit. A thorough inspection of your ducts is a critical step in diagnosing any cooling problem.
Leaky, Blocked, or Undersized Ducts
Leaky ducts are a major source of energy waste. Holes, cracks, or poor connections can allow as much as 30% of your cooled air to escape into unconditioned spaces like the attic or walls. Blocked ducts, whether from crushed sections or accumulated debris, can prevent air from reaching its destination, creating hot spots in your home. Similarly, if the ducts are too small for the system’s airflow, it creates high pressure and strain on the AC’s blower. As some homeowners have found, the problem might be with the “air ducts, not the HVAC unit itself,” making duct sealing and repair a cost-effective solution.
Solutions Beyond a Full Replacement
Discovering your AC is struggling doesn’t automatically mean you need to replace the entire system. There are several effective strategies that can improve your home’s comfort without the cost and disruption of a full HVAC overhaul. These solutions focus on either reducing your home’s cooling load or supplementing your existing system to handle problem areas. By thinking beyond the central unit, you can often find a more targeted and affordable way to solve your cooling challenges. Exploring these options with a professional can help you create a more comfortable and efficient living space.
Improve Your Home’s Efficiency
One of the best ways to help a struggling AC is to reduce the amount of work it has to do. This means improving your home’s thermal envelope to keep the cool air in and the hot air out. You can start by sealing air leaks around windows, doors, and electrical outlets. Adding insulation to your attic and walls can make a massive difference in preventing heat gain. Other strategies include installing energy-efficient windows, using blackout curtains to block solar heat, and planting shade trees on the south and west sides of your house. Each improvement lessens the cooling load on your AC system.
Add a Ductless Mini-Split System
If your cooling problems are concentrated in one or two areas—like a new home addition, a converted garage, or an upstairs bedroom that’s always hot—a ductless mini-split system is an excellent solution. These systems consist of an outdoor compressor connected to one or more indoor air-handling units. They are incredibly efficient and allow you to create independent temperature zones in your home. Installing a mini-split to supplement your central AC is often much more cost-effective than replacing the entire system, providing targeted cooling right where you need it most.
Install a Zoning System
A zoning system allows a single HVAC unit to cool different areas of your home to different temperatures. It works by installing dampers in your ductwork that can open and close to control airflow, all managed by separate thermostats in each “zone.” This is a great solution if your family has different temperature preferences or if you have a multi-story home where the upstairs is always warmer than the downstairs. Zoning can help your existing AC work smarter, not harder, by directing cool air only to the areas that need it, which can improve comfort and save energy.
Understanding Modern AC Technology
Air conditioner technology has advanced significantly over the years. Gone are the days when your only option was a single-speed unit that was either fully on or completely off. Today’s systems are much more sophisticated, offering variable speeds and stages that allow them to adapt to your home’s changing cooling needs with incredible precision. Understanding these modern features is key to choosing a new system that provides superior comfort and efficiency. These advanced systems run more quietly, offer better humidity control, and can lead to substantial savings on your energy bills compared to older, traditional models.
Two-Stage and Variable-Speed Systems
Unlike traditional single-stage systems that only run at 100% capacity, modern air conditioners offer more flexibility. A two-stage system has two speeds: a low setting (around 60-70% capacity) for mild days and a high setting for the hottest days. Variable-speed systems take this a step further, with compressors and fans that can adjust their output in tiny increments, running anywhere from 25% to 100% capacity. This allows the unit to precisely match the cooling demand at any given moment, providing a much more consistent indoor temperature and using only the exact amount of energy needed.
Benefits of Longer, Low-Speed Run Times
The ability of two-stage and variable-speed systems to run for longer periods at a lower speed offers huge benefits. These extended, gentle cycles are far more effective at removing humidity from the air, eliminating that cold-but-clammy feeling. They also provide more consistent temperatures, getting rid of the hot and cold spots common with single-stage units. Because the system isn’t constantly cycling on and off, it uses less energy, operates more quietly, and experiences less wear and tear on its components, which can contribute to a longer, more reliable service life for your investment.
Upgrade to the Right Size AC
You’ll immediately notice the difference when you replace your undersized AC with a properly sized unit that meets your needs. The whole-home cooling, the decrease in energy bills, and the quiet that comes with not running your unit 24/7 are sure to make your life a little more comfortable. To determine the best size AC unit for your home, consider these factors:
- House location: A lack of shade trees leaves you without relief from the heat, and many south and west-facing windows increase the temperature in the home.
- Window quality: Double-pane and triple-pane windows and low-E glass help reduce heat absorption and keep the cool air trapped inside.
- Household members: A large household produces more heat just by being in the home.
- Duct layout: An efficient duct layout ensures each room gets adequate airflow to cool your home equally throughout.
- Ceiling pitch and overhead fans: High ceilings can trap hot air. Overhead ceiling fans help move cool air by pushing it down and creating a wind column.
- Insulation: Insulation and airflow in your attic, crawlspace, and basement can impact your home’s temperature.
- Square footage: The size of your home in square feet helps determine the best size AC unit for you.
There’s a lot to consider when choosing an AC replacement for a larger home or undersized unit. For best results, consult with a certified HVAC technician. They have the knowledge and expertise to ensure you get a properly sized unit that meets your needs and budget.
Choose QRC for Your AC Needs
An undersized AC system works overtime to meet your home’s cooling demands, leading to higher utility bills and frequent repair costs. Replace your system to enjoy a comfortable North Carolina summer. QRC HVAC and Refrigeration offers over 50 years of experience helping residents in Winston-Salem and the surrounding area with their heating and cooling needs. Our friendly team of certified technicians has the expertise to tackle your AC issues quickly. Contact us today to learn more about our AC installation services or to schedule a repair.
Frequently Asked Questions
Certain rooms in my house are always much warmer than others. Is this a sign of an undersized AC?
Inconsistent cooling is a sign of an undersized AC, especially if you’re making every effort to cool the room. Try closing the windows and blinds, opening all ducts and vents, and opening the door for added circulation.
My AC runs constantly, but doesn’t seem to make a difference. Why is this?
If your AC can’t cool your home, it’s likely too small. Schedule a consultation with one of our technicians to learn more about potential solutions.
Are my energy bills unusually high during the summer? Could an undersized AC be the reason?
An undersized AC works overtime to meet your home’s demands, resulting in increased energy bills. Consider upgrading to a well-sized AC unit to enjoy a comfortable summer.
Key Takeaways
- Find Your AC’s ‘Just Right’ Fit: Bigger isn’t better when it comes to air conditioners. An oversized unit will short-cycle, leaving your home humid and wasting energy, while an undersized one runs nonstop without ever cooling your space, leading to high bills and early system failure.
- Let a Pro Do the Math: Sizing an AC correctly requires more than a square footage estimate. A professional Manual J load calculation is the only way to account for critical factors like your home’s insulation, window efficiency, and layout to ensure your investment performs efficiently.
- Rule Out the Simple Fixes First: Poor cooling doesn’t automatically mean you need a new unit. Before you budget for a replacement, check for common issues like a clogged air filter or leaky ductwork—these problems can mimic an undersized system and are often much easier to solve.
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