Step 7. Installation

Install the Equipment According to Manufacturer's Recommendations

The best equipment will not work well if it is not installed correctly. The goal of installation is to maintain the airflow of the fan so the ventilation system will perform as designed.


  • Always follow the manufacturer's installation instructions – especially the wiring instructions.
  • Some ceiling-insert products can be installed from below and some cannot. Check the manufacturer's instructions.
  • Make sure the damper at the outlet of each fan operates properly and is not blocked by screws during duct installation.
  • Don't use a recirculating range hood. Duct the range hood to the outside.


  • Keep duct runs as short as possible, using UL 181 ducting with a minimum of turns, to avoid resistance to air flow.
  • Make sure that all ducts are tightly and securely connected to the fan and to the wall cap, roof jack, or grille.
  • Flex duct has to be stretched tight to work efficiently. Cut off what you don't need – don't just loop it into a pile in the attic.
  • Support flex duct as it crosses trusses or rafters, following the manufacturers' instructions.
  • In cool or cold climates, use insulated duct or bury the duct in attic insulation to minimize condensation. Warm, humid household air rises up through the bath fan or whole-building fan and can condense in uninsulated ducting; sometimes condensate drains back to the fan and drips into the house.
  • Seal joints carefully, following the International Mechanical Code, which requires meeting UL 181 standards. Use screws for connections and mastic or approved metal tape to seal joints.
  • Fabric duct tape is neither tight nor secure, and it is not allowed in the building code for securing ducts to anything. It provides initial sealing but as the adhesive dries out, it becomes useless.
  • Wall caps and roof jacks restrict airflow, so choose them carefully. Look for devices with the simplest possible path for air movement, plus screening to keep out critters.
  • Don't terminate the duct from an exhaust fan in the attic or crawlspace or basement. Terminate the duct outside, sealed to a wall cap or roof jack.
  • Don't ever use dryer connector to vent a fan. It's not UL-approved for burying in a wall or ceiling.
  • Don't install an outdoor air intake near areas such as a car idling spot, dog run, or barbeque. Locate the outdoor air intake at least 10 feet away from pollutant sources.


  • Make sure ventilation controls are wired correctly so the system can operate as designed.
  • Test the controls to make sure the system operates as designed.
  • Label the controls for their purpose.