Simply closing your floor vents may not be enough to block the air. When you use a forced-air heating system in your home, you're bound to have heat registers too. Sections of duct work, like hallways in a school, run through your home's framing, carrying heated or cooled air to various rooms.etal Registers. Assuming the cover is temporary, and you'll wish to use the register again at some future date, simply get a magnetic vent cover to block a metal heat register in the floor. You can find these at hardware and other assorted stores.