When the air pressure in your home is lower than the air pressure outside, air will seek to find a way into your home. When air comes into the home via the stove pipe and brings in smoke, this is known as backdrafting. The smoke particles are bad for your health and can cause the contents of your home to smell like smoke. The odor from the buildup of creosote from inside the pipes has a an unpleasant sourness. Keeping the air from entering the stove pipe and exiting the stove involves reducing the difference between the inside air pressure and the outside air pressure.
When the wind blows against the side of your home it can create a high and low pressure zone on different sides. If the stove pipe coming from the roof is on the side of the home with high pressure, and the top of the pipe is below the high pressure zone, the air will rush down the pipe and into your home. Each house is different so there is no one-size-fits-all answer to how high the smoke stack should be. Caps also are available for the pipe to help minimize the effect of the air pressure from the wind.
Another source of the backdraft is a gas furnace that is operating. If the HVAC unit does not draw oxygen from an outside air vent it must draw from the home's supply of air to keep running. This reduces the air pressure in the home, encouraging air to rush in from every opening to the outside, including the stove pipe. This can be minimized when you are having problems lighting the fire in the stove because of the backdraft. Open a window in the room to allow the air pressure to equalize while lighting the stove.
Appliances that help create backdraft include bathroom and kitchen exhaust vents, central vacuum cleaners and clothes dryers. One or more operating at the same time might be enough to create a lower-pressure zone inside the home, and bring outside air down the stove pipe. Only use one at a time, and if the backdrafting still seems to be a problem, stop the appliance until the air pressure inside and outside equalizes.
Starting a Fire
Creating a fire in the stove heats the inside-the-stove air so that it has the energy to force its way up the pipe against the draft of air coming in. Getting the fire started, though, might be a problem with the cold air pouring into the fire chamber from the pipe. Place crumpled newspaper sheets as near the vent as you can and light them one at a time. This begins to heat the air in the pipe so that it starts to move upwards, pulling the inside air with it to the outside, instead of the reverse. Hold the paper with fireplace or other long tongs to avoid burning yourself.
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