Chimney Draft Issues 101

If you have a chimney, chances are that you have at least heard of chimney draft issues, even if you haven’t experienced them.

As we delve into the topic of chimney drafts, it’s important to first understand what a draft is and how it works. Draft is the term used to describe how air flows up a chimney or how gasses travel up the stack (which is why it is also referred to as stack effect). The temperature of the flue gasses come into play, as does volume, speed, and pressure.

How does chimney draft work?

Flue gasses move up the chimney because a vacuum is created. The pressure in the chimney is usually less than that outside of the house because of the temperature difference between the two. The draft effect is caused because the air inside the chimney is being pushed up by the air in the house.

In the winter, air outside is colder and heavier than that within the house. When air comes off of a fire, it’s hot and expands, causing it to be pushed up the chimney to the cooler air outside. If this doesn’t happen correctly, problems can occur.

Causes of draft common problems

Airflow issues

Draft problems can be caused by Dynamic Wind Loading. When wind is blowing on one side of the house and not the other, a vacuum can be created, sucking air out of the house. Air will pull down on the chimney, preventing it from exiting a home.

Fans

Bad draft can also occur when chimneys have to overcome fans (kitchen, bathroom, radon) in the house. It’s fairly easy for a fan to overtake fireplaces or wood stoves. This can be solved by allowing “make up air” in the house.

Air coming in

Sometimes, air blows down the chimney if the chimney is short or next to a larger building. This can also occur if a home is located at the base of a mountain. Raising the chimney to a proper height is a potential solution, as is adding a chimney stack.

If you have questions regarding air draft issues in your home, give CMO a call. We’ll be happy to take care of all of your chimney needs.