Most homes have fresh air (outside air) intakes generally located in the furnace area. Some have only a pipe that dumps air straight onto the floor, this causes cold, uncomfortable drafts in winter. The solution applied by most is to block the tube with paper, rags or whatever is handy to get rid of that awful cold air. This is a very dangerous solution. Why is that pipe there? To supply combustion air to the furnace and hot water tank burners. Without a good supply of combustion air a negative pressure can occur in cold weather. The cause is the cold outside air which is heavier than warm air flows down the chimney and into the home, this is known as a downdraft. When the furnace or hot water tank burner comes on it cannot overcome the cold air and instead of venting the gases (carbon monoxide, etc.) up and out of the chimney it vents these gases into the house, poisoning the air with carbon monoxide which is deadly. By providing a good supply of combustion air the pressure in the home stays positive. With a supply of combustion air the small amount of heat produced by the pilot light of the furnace or hot water tank or even just the warmer inside air is enough to maintain positive pressure. The fresh air intake ensures that a positive pressure will be maintained and enough air is present for complete combustion. Many homes are equipped with draft diverters as in the picture below at the end of the black pipe. This is only one type that is available for purchase at most home supply stores. If you have the old style air supply pipe with no diverter attached and the cold draft is a problem I suggest that you purchase one and install it. Never block the supply pipe, it could cost you your life.
Charlie Teets
Above Board Home Inspections
Calgary, Alberta
charlieteets@shaw.ca 
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