I had to call the HVAC company last week, because all the dust and odors from outside were coming into our home. It was like someone had switched the fan and it was blowing in instead of out. I immediately called the HVAC company. I knew this shouldn’t be happening. When I told the HVAC company what was happening, they sent a specialist over as soon as possible. He checked out the ductwork and told me that the problem was with the ductwork. There was a hole that was working like a vacuum and sucking up the air and dirt from outside. He said they had to have someone come in and repair the hole immediately. When the HVAC tech came out, he had special aerosol sealant that was released into the ductwork. The sealant was flowing through the ductwork and as it escaped through the hole; it gathered there and completely sealed it, along with any other areas that were allowing air to escape. The HVAC technician told me it was unusual for this to happen. Normally there would just be a lack of airflow. In our case, we ended up with a type of back draft. I was glad we had noticed it before there was any permanent damage to the HVAC system. I couldn’t believe how quickly we noticed the difference. I had a lot of cleaning to do when the HVAC technician was done with the ductwork, but the odors were quickly dissipating. I thanked the HVAC technician for his help and told him how happy I was that he was quick to find the hole in the ductwork.