Why One Airflow Hood Can’t Do It All

An airflow hood is one of the most common instruments contractors invest in — and one of the most misunderstood. The simple truth is this: There is no such thing as a “one size fits all” airflow hood.

Ernie Shortridge, who invented the flow hood in the late 1970s, never intended it to be the final authority on airflow — he intended it to be a proportioning tool.

Even with modern improvements, standard hoods can’t accurately measure very low flows (below ~70 cfm) because of the amount of free air that passes through. If you’re choosing a hood, the first question you should ask is: “What am I actually trying to measure?”

Are you measuring large filter grills? Low flow ventilation ducts? Commercial diffusers? Your answer determines the tool — not the brand name or the price tag.

Testing, adjusting, and balancing services graphic

Why Technicians Struggle with Instruments

I’ve done tech support for years now, both at NCI and Evergreen, and I can say this with confidence. Most field issues come down to one of two things:

  • The wrong instrument for the situation
  • Using the right test instrument incorrectly.

A classic example is the hot wire thermo-anemometer. It’s temperature sensitive, so you can’t use it in heat mode. Every winter, I’d get calls: “This bedroom is getting 400 cfm, but my windows are iced over!” No, you’re using a hot wire in heat. The instrument is reading incorrectly.

Every tool in your kit has an application — and a limitation.

Tools That Make Life Easier (and Safer)

One of Evergreen Telemetry’s most popular tools came directly from real world needs during COVID: the around-the-door probe. Hospitals across the country needed thousands of temporary isolation rooms, and traditional probes couldn’t measure
pressure without leaving doors cracked open.

This stainless steel probe lets you close the door completely while reading pressure — a small innovation that solved a massive problem. It’s also invaluable for reading a coil pressure drop without drilling holes. Many contractors stopped drilling units
altogether after adopting this tool.

It’s also ideal for reading static pressure on roof mounted exhaust fans, as illustrated in the NCI Commercial Air Balance manual.

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