Heavy fittings need support close enough to keep their weight out of the adjacent duct joints. If the fitting is hanging from the neighboring sections, add support before covering or loading the run.
Do not let a heavy fitting hang from the nearest joint.
Check
Identify what makes the fitting heavy: transitions, large elbows, tees, damper housings, volume dampers, coils, filters, sound attenuators, or inline equipment all create concentrated weight.
Check the approved hanger/support detail for required support near heavy fittings. Do not rely on normal straight-run spacing when a fitting adds concentrated load.
Look at whether the fitting is currently hanging from adjacent duct joints. If there is no dedicated support, the joint connections are carrying weight they were not meant to carry.
If structure above does not allow a direct rod, check whether a trapeze or alternate approved support detail can pick up the fitting from nearby structure.
Do not insulate or cover a heavy fitting that is missing its intermediate support. It is much harder to add after the run is closed in.
Steps
Identify what makes the fitting heavy: transitions, large elbows, tees, damper housings, volume dampers, coils, filters, sound attenuators, or inline equipment all create concentrated weight.
Check the approved hanger/support detail for required support near heavy fittings. Do not rely on normal straight-run spacing when a fitting adds concentrated load.
Look at whether the fitting is currently hanging from adjacent duct joints. If there is no dedicated support, the joint connections are carrying weight they were not meant to carry.
If structure above does not allow a direct rod, check whether a trapeze or alternate approved support detail can pick up the fitting from nearby structure.
Do not insulate or cover a heavy fitting that is missing its intermediate support. It is much harder to add after the run is closed in.
Say this to your foreman
There is no intermediate support directly under this [fitting type] at [location]. The nearest supports are [distance/location] away on each side. Do you want me to add a dedicated support here before we move on?