Matt, how do you calculate the proper airflow for a given tonnage of an HVAC system?

In this edition of “HVAC Skill Builder,” Matt discusses calculating the proper airflow for an HVAC system.

Matt, how do you calculate the proper airflow for a given tonnage of an HVAC system? Well, to calculate the proper airflow for a system, depending on the tonnage, number one is actually you have to do your load calculation and your manual S and your manual D, that’s part of the design series. But what you need to do is once you select a piece of equipment and you select the static in which you’re going to design the system, it should tell you the CFM that you’re going to have to design the system to. However, if you’re not doing a system design, you need to get in the ballpark of how much airflow a system may need. Usually an industry rule is 400 CFM of air per ton. So for example, if you have a two ton system, ideally you’re going to be looking for 800 CFM of air as the manufacturer says otherwise.