duct blasters test both flex and hard pipe ducting.
it is a great piece of equipment but there are others that perform as well
such as balomerers, pans & even blower doors. different diagnostics can be performed with a variety of equipment (all fun to work with...imho)
duct testing can also be done with a blower door, and blower door testing will test home & ducts where as duct blaster will only test ductwork.
the blower door identifies leaks by de-pressurization.
the bd pulls air from house, creating a negative pressure. this allows the amount of leakage to be measured. leakage sites are identified by feeling leakage from individual leakage sites.
I usually do a whole house leakage test then a room by room leakage for identifying each leakage.
Once this is done I test for duct leakage..still de-pressurizing.
This gives me the amount of duct leakage.
I've found that to then pressurize the ducts is the most effective way of pinpointing the duct leakage areas for hvac company or home owner to seal leakage areas. It is pretty hard to dispute that the ducts are leaking when you can feel the air blowingout of the leakage areas.
this type of testing is quite an eye opener for everyone, and is ideal for
reducing air leakage & improving efficiency of not only the duct work but also the building envelope.
The cure of the part should not be attempted without the cure of the whole. ~Plato