Using a tape measure from the interior side of the fascia backwards to the soffit 4 3/4 inches. It is important that the bevel of the nose is flush with the bottom edge of the fascia and the interior edge sits in the angle of the bevel. Using a pencil measuring 4 3/4 inches back from the interior side of the fascia on the soffit. Make sure that there is a clearance of 2 1/4 inch away from the rafter.
Using a hand drill place a 4 1/2 inch hole saw with a pilot drill bit place it on the pencil mark.
If replacing an obsolete vent that is already in place see if the existing hole meets the specified measurements of the new soffit vent. If not, remove the old vent, close up the hole and make a new hole.
If the existing ductwork is old or faded it is suggested that you buy a new one. If replacing the extension tube start by inserting it into the hold of the neck of the vent pushing it into the attic. This will give a better access to reaching it. When pulling it into the attic do not damage the exterior covering when pulling it through the hole in the soffit. Two people might be necessary, one pushing from the exterior and the other pulling tt within the attic.
Pull the extension tube until it reaches the exhaust fan. Take the end of the ductwork and place it on the neck of the exhaust fan. Attach it securely wi!h a jubilee clip and tighten the screw to hold it in place.
Brands of ductwork vary depending on the ductwork that is in place, Normally the ductwork for a bathroom exhaust fan has a thin membrane shelve in the interior of a plastic tube. Others have plastic tube with wrapped in insulation and a aluminum covering.