How To Make An Outdoor Fireplace Draw Better

An outdoor fireplace can be a delightful addition to any backyard, providing warmth and ambiance for gatherings or quiet evenings. However, a fireplace that does not draw properly can become a source of frustration, filling the surrounding area with smoke and rendering it unusable. A fireplace is said to "draw" when it effectively pulls smoke up and out of the chimney instead of allowing it to billow into the seating area. Improving the draw of an outdoor fireplace involves understanding the factors that influence airflow and implementing strategies to optimize these conditions.

The primary principle governing the draw of a fireplace is the stack effect. This principle relies on the difference in air pressure created by temperature variations. Warm air is less dense than cool air, causing it to rise. In a fireplace, the fire heats the air within the firebox and chimney, creating a column of rising warm air. This rising air creates a negative pressure zone that pulls air from the surrounding environment, including the firebox, up through the chimney. When this process functions efficiently, the fireplace draws well.

Conversely, a poorly functioning fireplace experiences disruptions to this natural airflow. Cold air downdrafts, obstructions in the chimney, or design flaws in the fireplace itself can all impede the upward movement of smoke. Understanding these potential issues is the first step in correcting a poor draw.

Ensure Proper Chimney Height

The height of the chimney is a critical factor in establishing a good draw. A chimney that is too short may not create enough draft to effectively pull smoke away from the firebox. As a general rule, a chimney should extend at least two feet above any part of the roof within 10 feet of it. This height requirement ensures that the chimney is above the turbulent airflow created by wind passing over the roof. Furthermore, the overall chimney height should be sufficient to create an adequate column of rising warm air. For most outdoor fireplaces, a minimum height of 10 feet from the firebox to the chimney termination is recommended. If the surrounding landscape includes tall trees or structures, additional height may be necessary to ensure proper draw.

Furthermore, consider the diameter of the chimney flue. The flue size should be appropriately sized for the firebox opening. An undersized flue will restrict airflow, while an oversized flue can allow the smoke to cool too quickly, reducing the draft. Consult a professional chimney sweep or fireplace expert to determine the optimal flue size for the specific fireplace design.

Altering chimney height is a significant undertaking that may require professional assistance. However, it is often a necessary step to achieve a properly functioning outdoor fireplace. Before making alterations, it is important to check local building codes and regulations regarding chimney height and clearances.

Eliminate Obstructions and Downdrafts

Obstructions within the chimney are a common cause of poor draw. These obstructions can be anything from bird nests and leaves to accumulated creosote deposits. Regular chimney cleaning is essential to maintain a clear and unobstructed flue. A professional chimney sweep can inspect the chimney for obstructions and remove any debris that is hindering airflow. It is recommended to have the chimney inspected and cleaned at least once a year, especially if the fireplace is used frequently.

Downdrafts, caused by wind pushing air down the chimney, can also disrupt the draw. Certain geographical locations or architectural features can exacerbate downdraft issues. A chimney cap can significantly reduce the effects of downdrafts by deflecting wind away from the chimney opening. Choose a chimney cap with a design that promotes upward airflow while preventing rain, snow, and debris from entering the chimney.

Another factor influencing downdrafts is the surrounding landscape. Tall trees or buildings can create wind patterns that force air down the chimney. Trimming back branches or strategically planting trees can help to mitigate these effects. Analyzing the prevailing wind patterns at the location of the fireplace can provide valuable insights into how to minimize downdrafts.

Optimize Firebox Design and Fuel Source

The design of the firebox itself can significantly impact the draw of the fireplace. A well-designed firebox will promote efficient combustion and direct smoke towards the chimney opening. Ensure that the firebox has sufficient air vents to supply oxygen to the fire. Insufficient air supply can lead to incomplete combustion, resulting in excessive smoke and a poor draw. The location and size of these vents are crucial for optimal performance.

The fuel source also plays a role in the quality of the draw. Wet or unseasoned wood produces more smoke than dry, seasoned wood. Dry wood burns hotter and more efficiently, creating a stronger draft. Ensure that the wood used is properly seasoned, meaning it has been air-dried for at least six months. Seasoned wood will have a lower moisture content, typically below 20%, and will burn with a clean, bright flame.

Consider the type of wood used in the fireplace. Hardwoods, such as oak and maple, generally burn longer and produce more heat than softwoods, such as pine and fir. However, softwoods tend to produce more smoke due to their higher resin content. Mixing hardwoods and softwoods can provide a balance between heat output and smoke production.

Finally, the way the fire is built can also influence the draw. Start with a small fire and gradually add larger pieces of wood. This allows the chimney to warm up slowly, establishing a draft before a large amount of smoke is produced. Avoid overloading the firebox with too much wood, as this can stifle the fire and create excessive smoke. Building the fire in a pyramid shape, with kindling at the bottom and larger logs on top, can promote efficient combustion and a strong draw.