If both systems are forced air systems it's possible to use the existing duct work; however, with out viewing you project, I would suggest having an air duct specialist evaluate your system to determine if modifications are necessary .
My parents did it with existing ductwork.
There should be a lever somewhere on the duct near the furnace. If it is open, the lever will be parallel to the duct. If the damper is closed, it will be perpendicular to the duct.
The heat it making the duct expand
To change a furnace air filter, first turn off the furnace. Locate the filter, usually near the return air duct. Remove the old filter and note the size. Insert the new filter, making sure it is facing the correct direction. Secure the filter in place and turn the furnace back on.
Don't laugh, duct tape.
I heard that you should have ducts cleaned but I don't know how often. How often should furnace duct cleaning be done and how much does it cost?
To maintain and clean furnace duct work for optimal performance and efficiency, it is recommended to schedule regular professional inspections and cleanings, change air filters regularly, seal any leaks in the ductwork, and ensure proper ventilation in the home.
The duct work does not need to be different from the rest just because of the I beam. Just be sure there is room so you do not compress it.
I would like to do some furnace duct cleaning but I am nervous. Do I need a special vacuum to do this? Will I get soot all over my carpet if I mess up?
Try looking where the return air duct connects to the furnace, if not there the next place to look is in the return air grille in the living space. Either way it is somewhere in the return air duct between the grille and the furnace.
It all depends upon your setup. You need to find where the return duct is connected to your airhandler/furnace. You could have a return filter grill or there is a door/panel on your airhandler/furnace that must be opened to replace the filter.
the filter on a central unit is the same as the furnace filter usually located in duct work directly beside furnace