Not a finished page once again, but some roughly presented information is better than none I hope you'll agree ;-) Semi-gravity This is the system layout most commonly installed from the 1960's through to about 1990.

I came to these conclusions after almost 40 hours of research, which included multiple conversations with five different duct tape companies, an email exchange with one of The Duct Tape Guys (a performance duo dedicated to everything duct tape) and my own extensive hands-on testing where I personally unspooled over 900 feet of tape during indoor and outdoor testing. Duct tape is the essential fill-in-the-cracks patching, sealing and hanging item.

They are inexpensive, widely available, and easily serviced by local contractors.

For many North American homes, they are a logical way to supply space heat.

The system can be made out of sheet metal, fiberglass ductboard, insulated plastic, or cloth.

Many times, a combination of these materials is used in the same home.