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Understanding Confusing HVAC Terms

Understanding Confusing HVAC Terms

Let’s be honest: Picking out a new heating and cooling system is confusing enough without having to decode every word the technician or consultant uses. Terms like “SEER” (does that have something to do with seersucker?), “tonnage” (in this case, not a measurement of weight), and “plenum” are coming out of the technician’s mouth but are not ringing a bell. It may feel as though the HVAC industry has a language of its own. With an abundance of acronyms and a variety of industry-specific terminology, it can make purchasing a replacement HVAC system or getting repairs done a little confusing. Well, today we hope to alleviate some of that confusion and help you understand some of the most common terminology you will hear in reference to your HVAC system. 

Residential HVAC System Equipment

Condenser/Outdoor Unit

This is the portion of the central air conditioning system that is located outside of the home. It functions as a heat transfer point for collecting heat from the home and dispelling it to the outdoor air. 

Heat Pump

A heat pump is an air conditioner that contains a valve that allows the season to alternate between heating and cooling.

Air Handler

The air handler is the portion of a central air conditioning or heat pump system that delivers heated or cooled air throughout the home ductwork. In some systems, a furnace completes this function.

Split System

A split system is a type of heat pump or central air conditioning system with components located both inside and outside the home. This is the most common design for residential use.

Package Unit

This year-round heating and air conditioning system has all of the components contained in one unit outside the home. 

Components of Your Unit


This pump moves refrigerant from the indoor evaporator coil to the outdoor condensing unit and then back to the evaporator. You might say that the compressor functions as the heart of the system as it circulates refrigerant through this loop.

Evaporator Coil

This is the portion of the heat pump or central air conditioning system that is located within the home. It functions as the heat transfer point for heating or cooling air.

Condenser Coil

The condenser coil is a network of refrigerant filled tubes where heat produces hot refrigerant vapor that then condenses into a liquid capable of absorbing more heat. 

HVAC Efficiency Measurements & Ratings


AFUE stands for annual fuel utilization efficiency and is a measure of a furnace’s heating efficiency. The higher this number, the more efficient the furnace. Currently, the government-established minimum AFUE rating is 81% AFUE.


BTU stands for British Thermal Unit and represents the amount of heat required to raise the temperature of 1 pound of water by 1-degree Fahrenheit. 


Standing for Heating Seasonal Performance Factor, HSPF is a measure of a heat pump’s heating efficiency. The higher the HSPF, the more efficient the heat pump. There is not a government-established minimum HSPF rating for heat pumps.


MERV stands for Minimum Efficiency Reporting Value and is the measure of an air filter’s efficiency. The higher the rating, the more efficient the filter is at capturing particles in the air. Generally, the highest-rated filter is MERV 16, which is a hospital-grade filter that captures the smallest particles in the air.


This stands for Seasonal Energy Efficiency Ratio and is the measure of the efficiency of an air conditioner. It’s calculated by taking the BTU/hour of cooling divided by the watts of electricity over one cooling season. The minimum SEER level is 13 with higher-performing models at SEER levels of 18, 19, 20, or higher. The higher the SEER rating, the more energy-efficient the system and the more you will save on your electric bills. 


Tonnage is a measure of the cooling capacity of an air conditioning system. It’s equal to the amount of heat needed to melt one ton of ice over 24 hours. One ton of cooling is equivalent to 12,000 BTU/hour. For example, a one-ton air conditioner would be rated at 12,000 BTU per hour.

Miscellaneous HVAC Terms

Balance Point

The balance point is when an outdoor temperature is equal to the exact heating needs of the home. This temperature is typically between 30° F and 45° F. Below this point, the heat pump will need to use supplementary electric resistance heat to maintain indoor comfort.

Load Calculation

The load calculation determines how much heating or cooling your home needs and is completed by an HVAC professional. It helps to determine the system size necessary for your home based on how much heat is gained or lost. 

Supplementary Heat

When a heat pump reaches its balance point, auxiliary or emergency heat, usually electrical resistance heat, provides an additional heating source. 


We hope this guide to commonly used HVAC terms has helped you in understanding how your HVAC system works. If you have additional questions, please do not hesitate to reach out to Peninsula Heating & Air at 804-642-6163. We’re here to help!

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