Things You'll Need
The small vents that are cut into the floor are heating and cooling registers, and in some rooms of your house there may also be some near or on the ceiling. These registers are connected to ducting that channels air from the central heating/cooling unit throughout your home. Sometimes you may need to block the flow of heat and air conditioning through one of the registers. If the vents are wood, it may be necessary to build your own airflow blocker. If your vents are metal, covering them takes much less effort.
Measure the size of the registers in the rooms you would like to block. Don't block more than 30 percent of the registers in your home. Blocking too many vents or ducts can create significant problems with air distribution, leading to poor heating/cooling performance and possibly damaging your furnace or other equipment.
Close off the airflow at each register by closing the register louvers, using a dial or lever on the side of the register. Metal registers typically have louvers, while wood and other custom registers often do not.
Close the in-duct damper, if available. Dampers are designed to restrict airflow to a register or branch ductwork. If your ductwork is accessible, look for dampers indicated by a small handle or other hardware on the outside of the duct. Turn the handle to close off the duct completely. Typically, the damper is closed when the handle is perpendicular to the length of the duct, but this varies by damper type and installation. Dampers may be located on ductwork in a basement or crawl space, or they can be found inside the duct near the register. In the latter case, you may need to use a mirror and flashlight to locate the damper.
Cover each metal register with a magnetic-sheet-type cover. They simply align with the edges of the register and magnetically cling to the top of the register.
Remove wooden or odd-sized registers using a screwdriver. Measure and cut cork sheeting to fit snugly into the inner frame on the back side of the register. Your cork sheet should fully block all airflow. Replace the register and secure it with the screws.
Hire a local HVAC specialist to perform an off-season evaluation of your home based on heated and cooled areas that are not in use. Some heating and air conditioning systems are negatively affected by blocking ducting. Ask about having areas professionally blocked for long-term solutions. Sometimes you can replace register vents with dummy vents. These are available at heating and air conditioning companies. You may still need to locate and close dampers.
Blocking heat and air conditioning may cause closed-off rooms to develop moisture-related problems, including mold and mildew growth, and can allow pipes to freeze during very cold weather. Allowing some heat into these rooms may be advisable.