Knowing if a HVAC system or fan is working efficiently for your customer is important and can be determined by the airflow it produces. Here are several techniques to measure airflow in an HVAC system.  

Measure Air Flow with a Device

Let’s start with the basics. First, airflow is usually measured in cubic feet per minute, known as CFM. We understand that this may seem a little overwhelming at first, but when using a device, it is actually pretty painless. An HVAC system or fan will list the recommended airflow in the owner’s manual, so you can compare the readings to that. 

Checking the Air Flow of Your HVAC with an Anemometer  

An anemometer is a device that measures wind speed and direction, so it only makes sense that it would be an accurate way to measure your HVAC’s airflow. 

The only issue technicians run into is that anemometers sometimes only measure in feet per minute. So, you will need to convert to cubic feet per minute. However, there are some anemometers out there that let you measure in cubic feet per minute.

Start by making sure the anemometer is on the setting to measure airflow. Then, hold the vane wheel next to the fan or the duct. It is best to hold in the direction of the airflow for the most accurate reading. Move the anemometer around to see airflow readings at different points. Remember, the readings will fluctuate, so to pause a particular reading, press and hold ‘pause.’ You can also toggle through the measurements taken to see the highest and lowest readings. This can give you a pretty good idea of the average airflow measurement. 

Converting FPM to CFM

If you do need to convert cubic feet per minute to feet per minute, you can use an online converter or try to do the math yourself with the following formula: Multiply FPM by pi, then multiple by the radius of the duct squared.

Using a Balancing Hood to Measure Air Flow

Another device that can be used for airflow measurement is a balancing hood. First, the balancing hood needs to be set to exhaust mode. Of course, read the manufacturing guide for complete instructions to receive the most accurate reading. 

Start by placing the hood over the exhaust fan grille. Make sure there is slight pressure upward to keep it over the grille firmly and not let any air escape, as this can cause a less accurate reading.  

What does the exhaust fan grille look like? It is usually a square or rectangular piece of metal that contains long slats to cover the fan or at the opening of the air duct. The exhaust fan grille is usually found on the floor or wall close to the ground or at times on the ceiling. 

The screen on the balancing hood will display the airflow in CFM. Keep in mind that this reading can fluctuate. This is because air volume is not always constant, so always take several measurements. 

When you are new on the job, things can seem stressful at first. Keep in mind this is how HVAC issues appear to most customers since they have no experience in the field. After being an HVAC technician overtime, you become a professional and can sometimes forget your customers are not as knowledgeable as you in this area. Take the time to explain to your customers the importance of measuring air flow to determine the efficiency of their HVAC system.

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