I recently purchused a forclosed home and have come to find that some of the duct work in the crawl space is in disrepair. The house was built in 1974 (not sure if it is original duct or not) What is the life span of crawl space duct work. Also, a previous owned bricked up the garage and built a subfloor and did run duck work into the room under the subfloor but the air flow is low in that room. Is that because they didnt replace the HVAC unit or because the duct is to small? I have a funny feeling that im going to have to replace th unit and all the duct work, does this happen alot?