Working in heating, ventilation, and air-conditioning (HVAC) means caring about how air is conditioned and distributed. It's only logical to have an understanding of the dynamics at play in duct airflow.

Most airflow issues and how to fix them

A duct system's viability is dependent on how well it distributes HVAC air. After all, convenience is the reason why HVAC systems exist. Comfort is out the window (pardon the pun) if the HVAC system isn't working properly. The building owner is then stuck with a duct system that serves no function.

That's why it's so important for HVAC technicians to learn about the most common airflow problems and how to fix them. Contractors, manufacturers, and distributors may incur additional expenses in the form of replacements and service calls due to improper HVAC airflow.

A Primer on Airflow in Duct Systems

The cooling system's evaporator coil. In an air conditioner, the evaporator coil is responsible for taking in warm air. It is generally accepted in the heating, ventilation, air conditioning, and refrigeration (HVAC&R) industry that 400 cubic feet per minute (cfm) per ton of air across the evaporator coil is adequate, while 500 cfm is ideal for heat pumps and 350 cfm is ideal for cooling applications that require removal of a lot of latent heat.

Accordingly, 1,200 cfm of airflow is required over the evaporator coil of a 3-ton home cooling HVAC system. For example, a 5-ton system needs 2,000 cfm of airflow, a 6-ton system needs 2,400 cfm, and so on.

Airflow problems in a home's duct system can be quickly identified by measuring the degree to which actual airflow readings differ from those predicted values.

How Static Pressure Affects Airflow in HVAC Systems

Static pressure is lost if air moves in a different direction. The pressure reduces as air flows across the evaporator coil. The larger the volume of air that flows over the evaporator, the larger the static pressure drop will be.

Manufacturers typically list the static pressure values of their HVAC units on their websites to aid HVAC technicians in measuring static pressure. Keep in mind that the evaporator coil's airflow might fluctuate depending on whether or not it is wet, hence many manufacturers provide two numbers.

The HVAC Mechanical Pro Troubleshooting course at Carrier University is just one example of how seriously Carrier Enterprise takes the topic of airflow and the education of HVAC professionals.

The main lesson here is that a well-functioning HVAC system relies on enough ventilation. As an HVAC contractor, realizing that is the first step toward making sure the system you install lasts as long as possible.

Conclusion

Check if the capacity of your air conditioning and heating equipment is appropriate for your dwelling. You don't want to over-condition your home with a unit that is too big, but you also don't want to leave too much space between the indoor and outdoor units. Problems arise in the home when the furnace is too big for the space. From excessive short-cycling to inefficient performance to a generally unpleasant environment.

A professional HVAC technician should be consulted for assistance in determining the proper furnace size. The technician needs to look at the entire house to make an informed decision about what size furnace to install.