Having proper airflow in your HVAC system is one of the most important factors in how efficiently the system performs and how long it lasts. Unfortunately, a fairly significant percentage of homes have various issues that prevent their HVAC system from having the correct amount of airflow.

General HVAC Airflow Requirements

The airflow an HVAC system produces is measured in cubic feet per minute (CFM), and every HVAC system must constantly produce a certain CFM for it to work properly. The level of airflow required for an HVAC system to operate effectively and efficiently depends on how many BTUs of heating or cooling. It also varies slightly based on the type of unit, such as an air conditioner, furnace, or heat pump.

The general rule of thumb for central air conditioners is that the system needs to have an airflow of 400 CFM for every one ton of cooling. One AC ton produces 12,000 BTUs of cooling. That means a 2-ton central AC system needs to move 800 CFM of air, and a 5-ton system needs to produce an airflow of 2,000 CFM. Central heat pump systems typically have slightly higher airflow requirements and need to produce 500 CFM per ton.

Calculating the necessary airflow for a heating system with a furnace is slightly different since it also depends on how efficient the furnace is, meaning what AFUE (annual fuel utilization efficiency) rating it has been given. All modern furnaces are either high-efficiency condensing units that draw air in from outside to supply oxygen to the burners or conventional induced-draft furnaces that just draw air in from the surrounding area. Condensing furnaces range between 90% and 98.5% AFUE, and almost all conventional furnaces are between 80% and 85% AFUE. What AFUE tells you is the total percentage of gas the furnace effectively uses to provide heat and what percentage is wasted.

The basic rule for condensing furnaces is that you need around 150 CFM for every 10,000 BTUs of heating produced. Nonetheless, this varies slightly depending on how efficient the furnace is with the highest-efficiency units having slightly higher CFM requirements. For conventional furnaces, you generally need around 130 CFM per 10,000 BTUs. The reason that condensing furnaces have higher airflow requirements is because this type of HVAC system needs to be able to pull sufficient air in from outside through the air intake vent while also having sufficient airflow to move air around the house at the same time.

Another thing to note about furnaces is that these numbers are based on a heating system installed in a building at sea level. As you increase in elevation, the air continues to lose its density. The result is that the CFM requirements increase the higher in elevation you are since it takes more force to move the thinner air found at higher elevations.

Understanding Why Proper Airflow Is Important

The heating and cooling performance of an HVAC system will never be as good as it should be if it doesn’t have sufficient airflow or if the airflow is too high. When the airflow is too low, you end up with much less coming into the system and much less conditioned air getting blown back throughout the house. That means your HVAC won’t cool or heat as quickly as it should, and the longer cooling/heating cycles will cause your energy bills to be higher.

Having too much airflow basically creates the same problems, just for a different reason. When the airflow is high, it results in air flowing through the furnace or over the AC evaporator coil faster than it should. That means your heating system won’t be able to add as much heat to the air flowing through it and your cooling system won’t be able to remove as much heat from the air. This again leads to poor performance and higher energy costs since it prevents your HVAC from raising or lowering the temperature in your house as quickly as it should.

Another reason proper airflow is so important is that it can make a major difference in how long your HVAC units last and how often they need to be repaired or have issues that prevent them from working. If your heating or air conditioning isn’t performing as well as it should, it increases the number of hours it must run for each year. That means the system will experience more wear and tear and almost always end up failing quite a bit faster than it normally would if it had the correct amount of airflow. Insufficient airflow can also lead to issues like overheating or the evaporator coil freezing up, which can result in damage that further shortens its life. The increased wear and tear can cause various components to wear out faster as well, leading to the system needing additional repairs.

What Can Cause an HVAC System to Have Airflow Issues?

It’s fairly rare for the airflow in an HVAC system to be too high since technicians should always test and calibrate the blower during installation to ensure that the system has the correct amount of airflow. If the airflow is too high, it generally means that your HVAC wasn’t properly installed or a technician made a mistake when servicing or repairing the system. The other possibility is that your ductwork is poorly designed and needs to be replaced.

Insufficient airflow is a much more frequent problem that can occur for a variety of reasons. It commonly happens due to running your HVAC with a dirty filter that restricts how much air the blower can bring in. Older ductwork systems also tend to have leaks that can greatly reduce how much air the blower can bring in and circulate around the house.

Another common problem that affects many HVAC systems is that their static pressure is too high. In HVAC terminology, static pressure is just another term for airflow resistance. As the static pressure or resistance in the HVAC system increases, it makes it more difficult for the blower to pull air into the return ducts and blow air back out of the supply ducts. The result is that you end up with the airflow being lower than it should. High static pressure can happen because the ducts are overly dirty and filled with a large amount of debris, the ductwork system is poorly designed and too small or for a variety of other reasons.

Contact the Pros

Crystal Blue Plumbing, Heating & Air is a locally owned and operated company that has been serving Sacramento and the surrounding areas since 1976. As one of the area’s leading HVAC companies, you can trust us to handle all your home’s heating and air conditioning needs. We offer expert HVAC maintenance, repair and installation services, and our team will do whatever it takes to ensure your HVAC system works just like it should. If you’re experiencing issues with poor airflow or any other problems with your air conditioning, heating, or plumbing, contact us today, and we’ll ensure the issue is solved in the most effective, most cost-efficient way.