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Excessive negative pressure may also cause the backdrafting of vented combustion equipment. Read the Application Warning on the front of this manual! Prior to balancing, ensure that: 1. All sealing of the ductwork system has been completed. 2. All of the HRV/ERV's components are in place and functioning properly. 3. Balancing dampers are fully open. 4. Unit is on HIGH speed. 5. Air flows in branch lines to specific areas of the house should be adjusted first prior to balancing the unit. A smoke