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Time to Dump the “Hand-o-Meter”

By Rick Kincel

It never ceases to amaze me that in this day of tech devices and instant information that we are still using the “Hand-o-Meter” for our primary method of measuring CFM.

Rick Kincel, Coburn Supply
Rick Kincel, Coburn Supply

We get calls here at Tech Support every day asking what the Superheat should be on any particular unit, or, is this Superheat a good number?

Let’s try this little experiment:

  • Run a unit with a fixed piston metering device.
  • Maybe you come up with 15 degrees of Superheat.
  • Lower the fan speed and the coil gets colder.

When the coil gets colder the Superheat decreases to let’s say 5 degrees:

  • Go back to the beginning.
  • Run a unit with a fixed piston metering device.

Maybe you come up with 15 degrees of Superheat again. Raise the fan speed and the coil gets warmer.

When the coil gets warmer the Superheat increases to let’s say 25 degrees,
notice that changing the CFM changes the Superheat; also notice that you never knew what the right CFM was.

So, if you don’t have the right CFM, then Superheat means nothing.

In this day of high efficiency equipment, the charge is critical, and the CFM needed to acquire the right charge DOES NOT GET SET AT THE FACTORY.

CPS and other manufacturers have come out with very user friendly flow hoods with the residential / light commercial contractor in mind. An example is the CPS ABM Hood 200, which is inexpensive, light, easy to hook up, and will produce a report right from its free software downloaded to your smartphone.

Every time I ask my students “How important is airflow?” the answers are always “10 out of 10,” “Real Important,” “Very Important.” Then when I ask how we are checking the “Huge Important” part of our industry the sheepish grins and downturned eyes always lead back to the “Hand-o-meter.”

It is my opinion that it is high time we dump the Hand-o-meter for CFM measurement and have it used for something more practical. When it comes to measuring CFM, velocity, Duct temperatures, and RH% on the problem jobsites, let’s invest in a Flow hood built for the Residential Light Commercial contractor.