If you have a fireplace, you know all too well the snug, toasty glow that it can bring to your house. But with that warm light comes the duty of keeping a clean, safe chimney. One part of that is using the right-sized chimney sweep brush. Using the wrong size can be ineffective for cleaning or even damage your chimney.
Whether you’re a DIY chimney cleaner or just want to understand what the professionals are using, selecting the correct brush size is essential for safety, efficiency, and chimney longevity.
Why Chimney Brush Size Matters
The right brush size isn’t just a matter of convenience—it directly impacts how well your chimney is cleaned.
Too Short: A brush that is shorter than your chimney’s diameter will glaze over creosote and soot on your walls and deposit toxic residue.
Too Big: A brush that is too large will be difficult to push through, wear out your chimney lining excessively, or get stuck altogether.
Your brush size for chimney should be the exact size and shape of your flue chimney. This will ensure full contact with walls so you can remove as much soot, creosote, and debris as you can.
Step 1: Familiarize Yourself with Your Chimney Flue Shape
You need to know the shape of your chimney flue first before you can choose the appropriate size of the brush. Chimney flues are most often found in three shapes:
Round – Characteristic of stainless steel or metal liners.
Square –
Usually found in older brick chimneys.
Rectangular –
Another common shape in masonry chimneys.
Tip: Shine a flashlight inside your chimney from the top or bottom (when safe and cool to do so). If uncertain, also measure from the top of the chimney with a tape measure.
Step 2: Measure Your Chimney Flue
The single most important process when choosing the right size chimney sweep brush is measurement.
For Round Flues:
Measure from one side to the other, along flue walls.
For Square or Rectangular Flues:
Measure both the width and height of the inside chamber.
Step 3: Match the Brush to the Flue Size
When shopping for your brush, you need to choose one that is the exact size of your chimney flue.
Pro Tip: If you can’t find the exact measure, always better to be a little larger, not smaller. A slightly bigger brush will still get the job done, but less so for a smaller brush will be covered in residue.
Types of Chimney Brushes
Other than size, brushes are constructed in different materials depending on your type of chimney.
Wire Brushes – Ideal for masonry chimneys, tough on creosote, but not for metal liners.
Poly Brushes – Best for stainless steel liners; not as harsh as wire, yet effective.
Flat Wire Brushes – Best for glazed creosote and heavy buildup.
Size Selection: Quick Reference Table
The following table is to help you pick the correct chimney sweep brush size according to common chimney size and shape.
Chimney Shape
Typical Flue Size (inches)
Recommended Brush Size
Brush Material Suggestion
Round
6″
6″ round brush
Poly for metal, wire for masonry
Round
8″
8″ round brush
Poly or wire
Round
10″
10″ round brush
Poly or wire
Square
8″ x 8″
8″ x 8″ square brush
Wire for masonry
Square
12″ x 12″
12″ x 12″ square brush
Wire for masonry
Rectangular
8″ x 12″
8″ x 12″ rectangular brush
Wire or poly depending on liner type
Rectangular
9″ x 13″
9″ x 13″ rectangular brush
Wire or poly depending on liner type
What If You Have an Odd-Sized Flue?
Not every chimney simply fits the “standard” sizes mentioned below. If your flue is not of standard size, you can:
Buy a slightly larger brush and trim the bristles to your exact size.
Buy a bespoke brush at a chimney supplies store.
Use a flexible head brush that is able to adapt to varying shapes.
One Quote to Remember
As master sweep John Thompson used to say:
“A clean chimney is more than a question of efficiency—it’s your first line of defense against a house fire.”
This reminder highlights why accurate brush sizing is not merely a technicality—it’s an insurance measure.
DIY vs. Professional Cleaning
Although most owners want to sweep their chimneys themselves, there are times when you should call in the experts. When you have heavy creosote accumulation, an extremely high chimney, or obstructions that are difficult to reach, using a professional ensures safety and thorough cleaning.
A professional will already have an assortment of brushes in different sizes, so you don’t have to worry about selecting the wrong one.
First-Time Chimney Brush Buyers Tips
Examine liner material prior to picking brush material.
Buy quality rods-low price rods will crack and get stuck in the chimney.
Protect yourself with gear like gloves, goggles, and a dust mask.
Sweep from top to bottom when possible for maximum soot removal.
Conclusion
The proper chimney sweep brush size is predicated on two key factors—your type of flue and your exact inside dimensions. Whether you choose a poly brush for your stainless steel liner or a wire brush for your brick chimney, matching the brush size with your chimney ensures a cleaner, safer fireplace.
By spending a few minutes to measure right and select the correct brush, you protect your home from chimney fires, optimize fireplace efficiency, and extend your chimney system’s life.
