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How To Know if You Have an Undersized HVAC System

undersized air conditioner

Are you struggling to maintain a comfortable temperature in your home? It’s possible that you have an undersized air conditioner. To ensure optimal performance, it’s crucial to have an AC unit that matches your home’s needs in terms of British thermal units (BTU capacity).

An oversized air conditioner can lead to short cycling and higher energy bills, while an undersized system can make your air conditioner work harder without reaching the desired temperature.

In this guide, we will help you identify whether your AC unit is undersized and what steps you can take to resolve the issue. Keep reading to learn more about how to achieve a comfortable and energy-efficient home!

Among the signs that you may have an undersized HVAC system, high energy bills stand out as a major concern. An undersize unit tends to work harder and longer to cool or heat your home, which can lead to decreased energy efficiency. This is particularly true when it comes to air conditioning systems.

The size of your AC system should be determined based on the square footage of your home. Generally, the bigger your home, the more powerful your AC system should be to effectively maintain a comfortable temperature.

If you’re experiencing high energy bills despite your efforts to conserve energy, it might be time to assess whether your current HVAC system is appropriately sized for your home’s needs.

2. Low Airflow

Another sign that you might have an undersized unit is experiencing low airflow throughout your home. An undersized AC often struggles to push enough air through the air handler to adequately cool or heat your space. An oversized unit on the other hand might cool or heat too quickly, resulting in short cycling and uneven temperatures. To create equal comfort levels in every room, it’s essential to have an HVAC system that can complete a regular cycle without overworking itself.

There are several possible causes of low airflow in an undersized unit:

  1. Inadequate air handler capacity: If your air handler is too small, it won’t be able to effectively circulate air throughout your home, leading to low airflow.
  2. Leaky or blocked air ducts: Air can escape through gaps or holes in your ductwork, or it can be obstructed by debris or insulation, reducing the airflow in your home.
  3. Clogged air filters: Dirty or clogged filters can restrict airflow, forcing your AC system to work harder and less efficiently.
  4. Frozen evaporator coils: When your AC unit is undersized, it might struggle to remove enough heat, causing the evaporator coils to freeze and further reducing airflow.

By identifying and addressing these issues, you can improve the airflow in your home, enhance HVAC system energy efficiency, and ensure that your HVAC system is working efficiently.

3. You're Getting Warm Air

This sign, specifically, is when your HVAC system is blowing warm air instead of cold air, indicating that your cooling capacity might be insufficient. An undersized condenser unit can struggle to remove more heat than it can handle, leading to warm air being circulated instead of the desired cool air.

This issue not only impacts your comfort but also causes additional wear and tear on your HVAC system as it works harder to compensate for the lack of cooling.

There are so many factors that contribute to this problem, but ensuring that your HVAC system is properly sized and well-maintained can help you enjoy a consistent supply of cool air throughout your home.

4. Inconsistent Room Temperature

Your air conditioners should provide consistent comfort throughout your home, maintaining the desired temperature in every room. When your air conditioner works inefficiently, it can lead to inconsistent room temperatures, impacting your overall comfort.

One of the main reasons behind this issue is the improper sizing of HVAC systems. A new HVAC system that is either too small or too large for your home can struggle to maintain a consistent temperature set point, resulting in some rooms feeling too hot or too cold.

Tips on Choosing the Right Size of HVAC System for Your Home

Choosing the Right Size of HVAC System

Selecting the right size of HVAC system for your home is crucial for maintaining consistent comfort and energy efficiency. An improperly sized unit can lead to uneven temperatures, increased energy bills, and reduced system lifespan.

  1. Consult HVAC professionals: The first step in choosing the right size of HVAC system is to consult with experienced HVAC professionals. They possess the knowledge and expertise to assess your home’s specific needs and recommend the most suitable system size.
  2. Determine your home’s square footage: Knowing your home’s square footage is essential in calculating the required heating and cooling capacity. Measure the length and width of each room and multiply them to find the area. Add up the areas of all the rooms to get the total square footage.
  3. Perform a load calculation: A load calculation is a detailed analysis that considers various factors, such as insulation levels, window types, and local climate, to determine the heating and cooling requirements of your home. HVAC professionals can perform this calculation to ensure you choose a system with the right capacity.
  4. Avoid relying on ‘big box’ store recommendations: While big box stores may offer a wide range of HVAC systems, their staff may not have the expertise to recommend the right size for your home. It’s best to consult with HVAC professionals who can provide personalized guidance based on your specific needs.
  5. Consider water vapor and humidity control: An HVAC system should also control the water vapor and humidity levels in your home. A properly sized system will effectively remove excess moisture, improving indoor air quality and preventing mold growth.
  6. Understand model numbers: HVAC system model numbers often indicate the system’s capacity. Familiarize yourself with these numbers to make an informed decision when comparing different units.
  7. Remember that not all HVAC systems are created equal: Different brands and models may have varying levels of efficiency and performance. Research and compare multiple options to find the best fit for your home.
  8. Factor in ceiling height: Ceiling height can significantly impact the heating and cooling requirements of a room. Higher ceilings require more energy to maintain a comfortable temperature. Ensure your chosen HVAC system can accommodate rooms with varying ceiling heights.
  9. Don’t oversize your HVAC system: Bigger is not always better when it comes to HVAC systems. An oversized system may cost more money upfront and lead to higher energy bills, increased wear and tear, and shorter system lifespan. Stick to the recommended size based on your load calculation.

Consider the maximum size guidelines: As a general rule, the maximum size unit you should buy would be 15% over the BTUs needed for cooling and 40% of the BTUs for heating. For heat pumps, the max is 25%, since they handle both cooling and heating.


Selecting the right size of HVAC system is essential for maintaining a comfortable and energy-efficient home. By consulting with HVAC professionals, performing a load calculation, and considering factors such as your home’s square footage, ceiling height, and humidity control, you can make an informed decision when choosing an HVAC system.

Remember that bigger is not always better, and adhere to the maximum size guidelines for optimal performance.

If you are in Phoenix and other nearby areas, and in need of professional HVAC service, feel free to call us here at Gladiate Air Conditioning & Heating.

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