Chimney odors and fireplace smells may be attributed to a multitude of different things. Fireplace smells come from creosote deposits in your chimney, a natural byproduct of burning wood. Chimney odors are usually stronger in the summer when the humidity is high, on rainy days, and / or when the air conditioner is running. As air moves down through your chimney, it brings the inner fireplace smells and chimney odors along with it. Tight sealing, top mounted dampers may help reduce or minimize the airflow (fireplace smells) coming down your chimney.

The real question isn’t why does your fireplace smell smoky: the question is why is the odor entering your house? The biggest air pathway to the outside in most houses is the fireplace chimney. A fireplace chimney can allow airflow in both directions. When in use, a fireplace chimney is a powerful evacuating force: the chimney updraft created by an open fireplace fire can move hundreds of cubic feet of air per minute out of the house, in many cases more air than the other pathways combined can supply! This is why you don’t smell the smoky odor when a fire is burning in the fireplace: it is only when the fire dies down, and the updraft diminishes to the point where evacuation from other sources overcomes it, that the airflow in the fireplace flue reverses and the odor returns.

What can you do to stop your house from using the fireplace chimney for makeup air? All you need to do is create enough resistance to the flow of air down the chimney so that the other air pathways will provide less resistance to nature’s tendency to equalize air pressure inside and outside the house. Here are some solutions:

  1. Close the fireplace damper when not in use. This will sometimes do the trick, although a damper alone may not provide sufficient flow resistance, as most fireplace dampers are pretty leaky.
  2. Consider installing a top sealing damper at the top of your chimney.
  3. This will provide a weatherproof barrier when you’re not burning a fire. The top sealing damper is opened and closed via a stainless steel cable running down the inside of the flue.Provide a source of outside air to your combustion appliances, so your gas furnace, oil furnace, woodstove and water heater aren’t siphoning air out of the house: the demand for replacement air will be reduced.