Terry's Tips are personal observations based on my experience and seeing the cause and effects of things. There may be many ways to address different problems and all opinions are welcome. I am always open to suggestions and certainly want you to correct me on any mistakes that might be written.
If you look and listen to your house, it will talk to you. Are you listening?
Do you have dark stains in your carpet along walls. Most likely you have a forced hot air heating system. At some point some builder or HVAC contractor though it would be a good idea to not install ducts and use building cavities as duct work. This is no longer permitted today, but I see this practice alot in homes built in the 80's and 90's.
Basically what you are seeing is air being sucked from the room through the carpet. The carpet is acting like a filter as the air passes through it. From an indoor air quality and efficiency stand point these systems are very poor. You are usually spending much more money to heat and cool your home because of the poorly installed duct work. Ideally you want your returns to only take conditioned air from the living space back to be re-conditioned. By having leaky duct work air can depressurize or pressurize spaces in between floors and walls. Air can be sucked from attic and crawlspaces where there are possible contaminants in the air. Loose supply ducts can be blowing air literally outside in some cases. Especially when mechanicals are installed in the attic outside the buildings thermal envelope.
What to do? First, I would hire an energy auditor to do a duct blaster test to see exactly how leaky the ducts are. If used in conjunction with a blower door the auditor can determine how much of the air is literally connected to outside. The results will determine the next action to take. It obviously can be expensive to open up walls an run new ducts.