Your HVAC Glossary: A Plain-English Guide to Common Heating and Air Terms

When you talk with a heating and air conditioning professional about your home’s system, it can sometimes feel like you have stepped into a conversation in a foreign language. Technicians, in an effort to be precise, often use industry jargon and technical terms that can leave a homeowner feeling confused and uncertain. Words like tonnage, SEER, and heat exchanger get used frequently, but what do they actually mean for your comfort, your safety, and your wallet? At 5 Starr Heating and Air, we operate on a simple principle: an empowered customer is a happy customer. We believe you have the right to understand exactly what is happening with your system and why we recommend a particular solution.

There is no good reason for this information to be confusing. The concepts behind how your HVAC system works are straightforward, and understanding the vocabulary is the first step toward making confident, informed decisions about repairs, maintenance, and new system purchases. Our expert-crafted guide is designed to serve as your plain-English translator for the world of heating and cooling. We will break down the most common terms you are likely to hear, explain what they mean in practical terms, and show you how they apply directly to keeping your Daphne home comfortable, safe, and efficient year round.

The Basics of System Performance and Efficiency

This first group of terms deals with the fundamental measurements of your HVAC system. They are the numbers that define how powerful your system is, how efficiently it operates, and ultimately, how much it costs to run. Understanding these core concepts is essential when choosing a new system or evaluating the performance of your current one.

One of the most important terms you will encounter is SEER, which stands for Seasonal Energy Efficiency Ratio. The simplest way to think of SEER is to compare it to the MPG, or miles per gallon, rating for a car. It is a direct measurement of your air conditioner’s efficiency. A higher SEER number means the unit uses less electricity to produce the same amount of cooling. As of 2023, a new standard called SEER2 is being used, which provides an even more accurate, real world measurement of efficiency. For homeowners in Daphne, where our cooling season is long and our air conditioners work hard for many months, a higher SEER2 rating translates directly into lower monthly power bills. While a higher efficiency system may have a larger initial investment, the energy savings can be substantial over the life of the unit.

Another term that often causes confusion is tonnage. This measurement has absolutely nothing to do with the physical weight of your air conditioner. HVAC tonnage is a measure of the system’s cooling capacity, or its ability to remove heat from your home. One ton of cooling capacity is the equivalent of melting one ton of ice over a 24 hour period. The size of your system is critical, and bigger is definitely not better. A system that is too small will run constantly and struggle to cool your home on the hottest days. A system that is too large, a common problem, will cool the space too quickly and shut off before it has had a chance to effectively remove our coastal humidity from the air. This leads to a cold, clammy feeling, inefficient operation, and increased wear and tear. Our technicians perform a detailed load calculation to ensure your unit is perfectly sized for your home’s specific needs.

For your heating system, the primary efficiency measurement is AFUE, or Annual Fuel Utilization Efficiency. This rating applies to furnaces and is expressed as a percentage. It tells you how much of the fuel your furnace consumes is converted directly into usable heat for your home. For example, a furnace with a 95% AFUE rating means that for every dollar you spend on fuel, 95 cents becomes heat, while the other 5 cents is lost through the exhaust process. If you have a heat pump instead of a furnace, its heating efficiency is measured by its HSPF, or Heating Seasonal Performance Factor. Just like SEER2, this standard was recently updated to HSPF2 for greater accuracy.

Key Components of Your Air Conditioning System

Your air conditioner is a complex system, but it is made up of a few key components that work together to move heat from inside your house to the outside. Understanding these parts can help you grasp what is happening when a technician diagnoses a specific problem.

The compressor is often called the heart of the air conditioning system. Located in the outdoor unit, its job is to pressurize the system’s refrigerant, a specialized fluid that absorbs and releases heat. By pressurizing the refrigerant, the compressor enables it to circulate through the system and carry out the heat exchange process. It is a major mechanical component, and a failure here is often one of the most significant and expensive repairs an AC unit can have.

That outdoor unit is also home to the condenser coil. The condenser’s function is to release the heat that was absorbed from inside your home. As the hot, high pressure refrigerant flows through the coils, a large fan pulls outdoor air across them, allowing the heat to dissipate into the atmosphere. This is why keeping that outdoor unit clean and clear of debris, grass clippings, and bushes is so important. A dirty condenser coil cannot release heat effectively, which forces your compressor to work harder, drives up your energy bills, and can lead to a system breakdown.

The counterpart to the outdoor coil is the evaporator coil, which is located in your indoor unit. This is where the cooling actually happens. The cold, low pressure refrigerant flows through these coils, and as your home’s warm air is blown across them, the heat is absorbed into the refrigerant. This process also removes humidity from the air, which is critical for comfort along the Gulf Coast. The moisture condenses on the coil and is drained away. If airflow to the evaporator coil is blocked, most often by a dirty air filter, it can get too cold and freeze over, stopping the cooling process entirely.

Understanding Your Heating System

Whether you have a furnace or a heat pump, your heating system also has several critical components that are essential for safe and effective operation during the cooler months.

For furnaces, the single most important safety component is the heat exchanger. This is a sealed metal chamber, or a series of tubes, where the combustion process takes place. The hot exhaust gases from the burning fuel heat the metal walls of the chamber. Your home’s air, propelled by the blower motor, circulates over the outside of the heat exchanger, picking up the heat before being distributed through your ductwork. The key here is that the exhaust gases and your home’s air should never mix. Over time, the metal of the heat exchanger can develop cracks from stress. A cracked heat exchanger is a serious safety hazard because it can allow carbon monoxide, a deadly and odorless gas, to leak into your home’s air supply. This is the primary reason why annual professional furnace inspections are not just recommended, they are essential for your family’s safety.

The blower motor is the powerful fan that moves air through your home’s ductwork. It is a true workhorse, operating year round for both your heating and air conditioning cycles. Some modern systems feature a variable speed motor, which can run at different speeds to provide more precise airflow. This results in more even temperatures, better humidity control, and quieter operation compared to a standard, single speed motor.

Finally, you will hear about the ignitor or pilot light. Very old furnaces used a constantly burning pilot light to ignite the gas burners. Modern furnaces are much more efficient and use an electronic ignitor. This device, often a hot surface ignitor, heats up to a glowing red hot temperature to light the burners only when your thermostat calls for heat, saving a significant amount of fuel.

Air Distribution and Quality

Your HVAC system creates comfortable air, but the distribution system is what delivers it to you. These components are just as important for your overall comfort and efficiency.

Your home’s ductwork is the network of channels, often running through an attic or crawlspace, that acts as the circulatory system for your heated and cooled air. Leaks, disconnected sections, or crushed ducts are incredibly common and wasteful. Leaky ductwork can lose a significant percentage of your conditioned air into unconditioned spaces, forcing your system to run longer to heat or cool your home. It can also pull dirty, dusty air from your attic or crawlspace directly into your air supply, negatively impacting your home’s air quality.

The final stage of air quality control is your air filter. Filters are rated using a system called MERV, which stands for Minimum Efficiency Reporting Value. The rating, which typically ranges from 1 to 16 for residential systems, indicates how effective the filter is at capturing airborne particles. A higher MERV rating means the filter can trap smaller particles, like pollen, mold spores, and pet dander. However, there is a trade off. A very high MERV filter can also be more restrictive to airflow, which can put a strain on your system’s blower motor. It is important to choose a filter that provides the level of filtration you desire while still being compatible with your specific HVAC system.

We hope this guide has helped to translate some of the more common HVAC terms and demystify how your system works. Our commitment at 5 Starr Heating and Air is to always communicate with you in clear, understandable terms. We want you to feel confident in the work we do and the recommendations we provide. When you call us for service in the Daphne area, you will get expert advice without the jargon, just straightforward solutions to keep your home comfortable and safe.