Tell someone or document it before you close it up.
Duct transition too abrupt at fan/equipment
A transition that changes size too sharply at a fan or equipment connection can hurt airflow before the air even reaches the run. Check the submittal and approved layout before connecting and sealing it.
Do not force a transition to make a wrong opening, bad layout, or blocked access look acceptable.
Check
Check the equipment submittal for inlet/outlet connection requirements, straight-duct needs, transition limits, or manufacturer notes near the fan or equipment opening.
Look at the transition shape. A gradual taper is usually easier on airflow
a sudden size change, hard step, or abrupt square-to-round immediately off the fan is the concern.
Check whether the transition is being used to hide another problem, such as a wrong opening, bad layout, blocked access, or misaligned equipment connection.
If the transition is already fabricated and appears too abrupt for the submittal or project standard, the likely fixes are a longer transition, added straight duct, or a corrected shop piece.
Do not connect and seal a transition you already suspect will create airflow, noise, or TAB trouble.
Steps
Check the equipment submittal for inlet/outlet connection requirements, straight-duct needs, transition limits, or manufacturer notes near the fan or equipment opening.
Look at the transition shape. A gradual taper is usually easier on airflow
a sudden size change, hard step, or abrupt square-to-round immediately off the fan is the concern.
Check whether the transition is being used to hide another problem, such as a wrong opening, bad layout, blocked access, or misaligned equipment connection.
If the transition is already fabricated and appears too abrupt for the submittal or project standard, the likely fixes are a longer transition, added straight duct, or a corrected shop piece.
Do not connect and seal a transition you already suspect will create airflow, noise, or TAB trouble.
Say this to your foreman
The transition at [unit tag/location] changes from [size A] to [size B] over about [distance] near the fan/equipment. I think it may be too abrupt for the submittal or airflow. Do you want me to check the manufacturer requirement before we connect it?