Performing Under Pressure

5 Facts About KEES Pressure Relief Doors

September 27, 2023

KEES positive- and negative-pressure relief doors prevent damage to ductwork exposed to pressures exceeding design conditions due to unintended duct damper closure, excessive blower RPM, or other circumstances causing duct conditions outside the normal designed operational range. The doors feature an adjustable latch which is factory preset to release the door from its closed position at a specified pressure threshold. The closure springs automatically return the door to its closed position when the excessive pressure condition is no longer present.

Here are 5 things to know about KEES pressure relief doors:

  1. Recommended relief airflow is based on 75% of the total system CFM.
  2. The recommended relief pressure setting is one-inch water gauge beyond the system’s normal operating static pressure (1” higher for positive pressure ducts and 1” lower for negative pressure ducts).
  3. Pressure relief doors must be mounted vertically with the hinge at the bottom of the door to ensure that the closure springs automatically close the door.
  4. Because the closure springs limit the amount the doors open, KEES pressure relief doors are not intended to be used as duct access doors. Standard duct access doors (ADH or ADC) are suitable options.
  5. The doors do not need to match the size of the duct. (See Figure B below for recommended sizing).

Relief Airflow vs Static Pressure
Recommended Relief Door Sizing Chart

KEES offers pressure relief doors that open outward for positive pressure (Model BO) and inward for negative pressure (Model BI) in a full range of standard sizes with custom dimensioning available upon request. Standard construction is galvanized steel with available options that include stainless steel construction, viewports and insulation.