It is rather amazing to think that duct was put in where leaks and under-sizing and flex lengths were exceeded, but we see it everyday as we help our customers. Some was a result of short cuts taken during the building boom, and I am sure it would still be happening if the codes had not been given some "teeth" to make sure all contractors were doing their best to make a tight system. So as we go from project to project - we try and improve what is there and always do the most metal duct, avoiding flex, and sealing we can do on the new system.