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IWC ( Inches Water Column )

In a recent survey conducted at the National Balancing Institute, less than 6% of the companies surveyed said they measured static pressures on a regular basis. In fact, many companies make the mistake of measuring static pressure only as a last resort when they're in trouble and have exhausted all other traditional testing.

History tells us that our industry measured static pressure many decades ago. When and why did we lose the habit of testing this basic factor that affects the total efficient operation of the heat and air system? How and why did we lose touch with the air side of HVAC systems?

Years Ago it was the "U-tube" . . .

Years ago a method of measuring air flow and air pressure was required, and the "U-tube" was used. This instrument is still used today. It's a 1/4-in. tube formed into a 'U' shape. A scale is written on it in inches, and it's filled half-full with water. I still had one when I retired from the business.

When pressure is collected in the duct with a static pressure tip. The pressure travels through the hose to the manometer, or pressure reading gauge. The distance the pressure moves the water is Inches of Water Column or (IWC).

Modern instruments usually use pressure sensors to interpret the readings digitally, which makes our jobs much easier. But the old liquid-filled gauges still do the job, if that's all you have to get started.

How long does it take to read static pressure? About five minutes. Drill holes into the duct or equipment to insert your static pressure tip, set up the pressure measuring gauge, and read and record the supply and return sides of the system for a total static pressure reading, and is taken ahead of the Evaporator Coil. That's all there is to it.

1 inch of water [4 °C] = 25.399 999 83 kilogram-force/square meter