© 2006 GE ECM by Regal-Beloit
- 45 -
Indoor Blower Motors
v0.2
ESP is simply the difference in pressure between the supply side of the system and
the return side of the system. Keep in mind that the return side static is negative
pressure since the air is being pulled through the duct, and the supply side static is
positive pressure since the air is being pushed through the duct. Static pressure is a
measurement of how much resistance there is to airflow in the duct system on both
sides combined.
Most furnaces recommend a maximum ESP of .5 in. wc. However this
recommendation may be different on air handlers and package systems. Always
follow the OEM’s specification. This information should be listed on the equipment
data plate or in the factory manuals.
On the diagram below the reading is taken under the evaporator coil for the supply
reading and the after the filter for the return reading, in relationship to the direction of
the flow of air. Furnaces are typically rated for ESP without the evaporator coil and
filter included, which means we have to include them in the external static pressure
of the ductwork that the motor must work against to move air.
The incline manometer shows a reading of .5 in. wc. from a combined total of .15 in.
wc. return and .35 in. wc. supply.
Air Filter
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