Having sufficient airflow is one of the biggest factors in how well a cooling or heating system works. Any ducted, forced-air HVAC system requires a specific airflow rate to work effectively and energy efficiently. If there isn’t a sufficient volume of air circulating through the system, the cooling and heat output will be greatly reduced. Insufficient airflow also leads to greater energy waste and higher energy costs. It also puts extra strain and increases the wear on the AC, furnace or heat pump as well as the blower. In this article, we’ll explain everything you need to know about airflow rates, why they’re important and what issues can contribute to your HVAC system having poor airflow.

Understanding Airflow Rates and Why They Matter

The volume of air that needs to circulate through the system depends on the size of the AC or other HVAC unit. To work effectively, a system needs to circulate 400 cubic feet of air per minute (CFM) for every 1 AC ton. To effectively cool a 1,000-square-foot home in the San Diego area, you usually need a system that produces between 50,000 and 55,000 BTUs of air conditioning. One AC ton is equal to 12,000 BTUs, which means the system would need a 4.5- or 5-ton AC and would need to produce 1,800 to 2,000 CFM of airflow.

The volume of airflow an HVAC system can produce depends on the size of the ducts, the layout of the ductwork and how powerful the blower is. If the ducts are too small or the duct system isn’t properly designed and installed, the airflow will be restricted and the system won’t be able to move a sufficient volume of air for it to cool or heat effectively. If there isn’t a sufficient volume of air constantly moving through the system, it will often also lead to issues like the AC evaporator coil frequently freezing or a furnace regularly overheating.

Static Pressure Explained

Static pressure is a technical term that refers to the amount of airflow resistance there is inside a ducted HVAC system. In ideal conditions, an HVAC system will have quite low static pressure so that the air circulates through the ducts easily. Unfortunately, the majority of HVAC systems have various issues that contribute to high static pressure. In fact, high static pressure is one of the biggest, if not the biggest, contributors to energy waste in most homes.

High static pressure is a major problem, as it can greatly reduce the airflow rate. This means that the system won’t circulate a sufficient volume of air. If the system isn’t circulating enough air, it will take a longer time for it to fully cool or heat the home to the desired temperature, leading to increased energy consumption.

High static pressure can also lead to comfort issues, as it makes it harder for the blower to circulate air through the entire duct system. The more centrally located rooms where the vents are closer to the air handler will usually still receive sufficient cooling or heating. However, high static pressure will typically reduce the volume of air that flows out of the vents toward the end of the various duct branches. This often results in the rooms supplied by those vents remaining hotter than you want in the summer and cooler in the winter since they aren’t receiving adequate airflow.

High static pressure can also cause blowouts at various points in the duct system. This results in holes or gaps in the duct connections or joints that allow lots of air to leak out. This can have a cyclical effect, as air leaks lead to the static pressure increasing which can in turn lead to more air leaks.

If your HVAC system runs loudly, it also often means that the system has high static pressure. When the static pressure is too high, you’ll be able to hear the air flowing through the ducts more easily. High static pressure also increases the workload on the blower, which can make it run more loudly.

Issues That Can Contribute to Decreased Airflow and High Static Pressure

If you’re having issues with your HVAC system not working effectively, a technician can measure the airflow rate and static pressure to find ways to improve the system’s efficiency and effectiveness. In some cases, the issue is simply that the blower is beginning to wear out or is too dirty, both of which will prevent it from circulating the necessary volume of air. Keeping the blower clean is one of the many reasons why annual HVAC maintenance is important. When servicing your HVAC system, the technician will also test the blower so that you can then get it replaced if it is starting to wear out or isn’t the correct size for your system. If your HVAC system has any of these other issues, it can also contribute to poor airflow and/or high static pressure.

Old or Damaged Air Ducts

Any time you replace any HVAC unit, it is important to have your ductwork inspected to ensure the new unit works effectively and the system has proper airflow. There is simply no point in pairing a new, energy-efficiency HVAC unit with an extremely old, damaged or leaking ductwork system. If you do, it will lead to the new unit not being nearly as energy efficient as it should be. Air ducts usually only have a lifespan of 25 to 30 years at the most, and they should also be fully resealed at least every 10 years.

Clogged or Too Restrictive Air Filter

The air filter in an HVAC system can make a massive difference in terms of static pressure and airflow rates. If the filter isn’t replaced frequently and clogs up, it will significantly restrict the airflow coming into the system and how much air it can put out. Using an air filter that is too efficient will also essentially have the same effect as running the system with a clogged filter. If your HVAC system is fairly new, you can possibly use up to a MERV 12 filter. However, a MERV 12 filter will often be too restrictive in an older system.

Closed or Obstructed Supply Vents

To achieve proper airflow, all of the supply vents in a home need to be fully open. It’s also important that the vents are unobstructed so that air easily flows out of them. Closed or obstructed vents will always lead to higher static pressure and restrict how much air the system can move.

Inadequate Return Air Ducts and Vents

HVAC systems are a closed loop. Air is first drawn into the system through the return air vents and then travels through the return ducts to the furnace or indoor AC unit before finally circulating through the supply ducts and flowing out of the supply vents. Many older homes have issues where they don’t have a sufficient number of return air vents or the return ducts are too small. These issues will reduce the amount of air coming into the system and lead to it not circulating sufficient CFM of air to work properly.

If your cooling or heating system isn’t putting out enough air or has any other issues, you can trust the HVAC experts at Comfort Bros Heating, Air & Plumbing for help. Our team works on all makes and models of cooling and heating equipment and is ready to take care of your HVAC repair, maintenance and installation needs. Give us a call today if you need an inspection or any other HVAC service in El Cajon or the San Diego area.

Meet the Author
Travis Smith
Travis Smith

Travis Smith started in his family's Heating and Air Conditioning business at 6 months and 5 days old "helping daddy do trim outs". He then worked at Sky Heating & AC for over 22 years before partnering with the Comfort Bros.
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