Had 3 estimates done to change out hvac system.

All 3 suggested addressing the plenum to increase airflow.

[current plenum](https://imgur.com/a/kWeXWen)

Company 1 suggested putting turning vanes in. Company 2 simply stated they would just put sheet metal inside the plenum to direct airflow (probably very cheap) Company 3 suggested making the boxy plenum to have flared bottoms.

In addition to addressing the boxy plenum all 3 said the new furnace would be on a box to help with airflow, unlike my current furnace that sits directly in the floor.

My thought. Would a combination of the plenum with flared bottoms and turning vanes work? Or would doing both the flared bottom and turning vanes in the plenum cancel each other out or make a difference?

I have a trunk line that is by a steel beam. It is connected over top of the steel beam.

[Trunkline above steel beam](https://imgur.com/a/6JoJO3T)

Company 1 suggested putting turning vanes in both trunk lines above the steel beam, again to help with airflow. Company 2 simply stated they would just again put sheet metal in to direct airflow, just like the plenum (probably very cheap) Company 3 stated nothing needed to be done to the trunk line above the steel beam since I would be installing a 2 stage variable speed furnace, and that would take care of it. Company 3 said do nothing because the furnace would take care of it?

Which of the above companies has the best idea to address the trunk line?

Company 1 & 2 both said that this is pretty common for trunk lines to be done this way around steel beams since they want to save head room in case the basement is ever finished.

In the trunkline by the steel beam, I get decent airflow if I have the inline dampers adjusted correctly. I do have a supply damper on that trunkline closed completely since we are never in that room.

Now Im changing out my current single stage Carrier 52mcb100-16 furnace to an American standard S9V2 2 stage variable speed furnace installed

Thanks for any insight. I greatly appreciate it.