I recently switched from oil to gas and decided to upgrade my cooling system as well. Last year I noticed condensation coming from the main vent but didn’t think it was anything major since the cooling system worked great -so ignored it. My plumber brought to my attention the issue I noticed and ignored from last year only this time it was not just water. You could visibly see a ton of mold growing on the outside of the vent. It was completely inundated with water and mold- it was disgusting. I thought I was going to need new ducts. Dr. Green Thumb came and took care of everything at a very reasonable price and I did not need new ducts. I highly recommend them for any air duct cleaning service you need. I really wish I could share before and after pictures of my ducts. True professionals- I give them two thumbs up!