It also helps to clean the AC duct work.

I've just had a 3 ton electric system installed, with all of the ductwork for $ 4200I had a 2.5 ton electric system, with existing ductwork for 3200It all depends on the size, the system and the hvac company

The cost of installing 2 units and duct work was around $13k. 

Come to find out there were air handlers and duct work in each unit and A/C too, the kicker is, the heating portion was electric elements, not gas.

The ducts, ductwork, filters and even walls and ceilings near the ductwork can be contaminated.

Is the insulation around the duct work in good shape? 

I want to keep the duct-work in case I need it later. 

They have to have a water source , cut into the ductwork .Its not a DIY project .

Is there already ductwork through-out?

Your talking new HVAC (ductwork?)