Arkansas HVACR NewsMagazine May 2025 Issue

HVACR NewsMagazine May 2025

Tech News

If you don’t have a dual port manometer, you can use one with a single port to take the readings. Take the first measurement from the point above the blower motor but before the coil. In our case, we are using the thermal limit switch hole. The picture below shows a measurement of 0.85” WC.

Step 5: In order to take the second measurement, drill a small 3/8" diameter hole, using a step bit, into the supply plenum above the evaporator coil. If using a dual port manometer, add the second static pressure tip to the negative side of the digital water column manometer. Insert the static pressure tip into the hole with the tip facing downwards to measure the static pressure of the supply plenum downstream of the coil.

The second measurement is downstream of the coil and in the supply plenum. This measurement is 0.18” WC.

Step 6: The image below shows a pressure drop of 0.67” WC across the coil because the dual port digital manometer is automatically subtracting the downstream measurement of 0.18" WC from the initial measurement of 0.85" WC to equal 0.67"WC.

Subtract the second measurement from the first to determine the static pressure drop. 0.85” WC - 0.18” WC = 0.67” WC. This is the same calculation we got from using our dual port manometer.