At Bonfire, chimney sweeping involves much more than just clearing away soot and debris. We carry out a range of thorough safety checks and tests to confirm that your chimney is safe for use.
Below is an outline of the different tests we perform to detect any potential issues. If you’re uncertain whether your current chimney service provider is performing these essential checks, it may be worth considering a change.
Require any of these services? Call us on 0118 970 1717 or email info@bonfire.co.uk
Chimney Calculation For Open Fires
Using the top of the range software, we can precisely calculate the correct opening size and draw for an open fireplace which is crucial to ensure efficient operation and safety.

The fireplace opening in your home might have been previously compromised meaning that it will not draw or function properly. The opening must be proportionate to the room size and the chimney flue to prevent smoke from entering the room.
Typically, the flue area should be around 10% of the fireplace opening size to create the proper airflow. Adequate ventilation is also essential to maintain a steady draw, ensuring the smoke is carried out of the chimney effectively.
Chimney Airtightness Test (Smoke Test 1)
This test is designed to check the airtightness of your chimney by using smoke to reveal any leaks. It’s typically carried out when a new appliance is installed in an existing chimney or when a chimney is re-opened after a long period of disuse. It’s also useful if smoke is suspected of leaking into your home or neighbouring properties.
To conduct the test, the flue is first warmed. Then, a number of smoke pellets are lit in the fireplace, and the chimney pot is sealed once smoke reaches the top. While the smoke is contained, we closely inspect the chimney for any signs of leakage. Any smoke escaping from the chimney walls indicates a failure in airtightness that will need to be addressed.
Chimney Ventilation Test (Smoke Test 2)
This test checks the chimney’s ability to efficiently draw out smoke, ensuring that there’s enough ventilation in the room for safe use of the chimney. Unlike the airtightness test, the ventilation test does not check for leaks, as it doesn’t involve sealing the top or bottom of the chimney.
During the test, all doors and windows in the room are closed, and the flue is warmed for about 10 minutes. A smoke pellet is then ignited in the fireplace, and we observe how well the smoke escapes from the top of the chimney. If there’s any backflow of smoke into the room, additional ventilation may be required.
Flue Leakage Test
This test measures how much air is leaking from the flue and whether it meets the allowable limits set for safe operation. It’s commonly used for manufactured flue systems like rigid flues or flexible liners.
We use a leakage testing device to pump air into the flue, and the amount of pressure is measured to determine the rate of leakage. The results are printed for review, and we compare them to the required standards for safety and efficiency.
Flue Draught Measurement
This test measures the strength of the airflow through the chimney, ensuring that combustion gases are being safely drawn out. It’s particularly important when commissioning a new stove.

After warming the flue to its operating temperature, a flue draught gauge is inserted to take a reading. The result is compared to the manufacturer’s guidelines, and if the draught is too weak, remedial work will be necessary.
Draught Interference Test
To ensure that other appliances, such as extractor fans, aren’t interfering with the chimney’s operation, we perform a draught interference test. With the stove burning, all internal doors are opened, and extraction fans like kitchen or bathroom vents are switched on to their highest settings. The chimney draught is then measured to ensure it’s within the acceptable range, despite the extra airflow from these appliances. If the draught dips too much, adjustments may be needed to prevent any potential problems.
Core Ball Test
This test is used to confirm that the flue is free from obstructions and that it meets the minimum diameter requirements for safe operation. A weighted ball, known as a core ball, is lowered down the chimney to check for any blockages, such as bird nests or debris. If an obstruction is encountered, it’s cleared before the test is repeated.
Refuel Spillage Test
This test ensures that when you open your stove’s door to add more fuel, smoke doesn’t spill back into the room. Once the stove is at its normal operating temperature, we open the door and use a smoke match to see if smoke escapes into the room. This process is repeated with all extractor fans running to ensure the chimney can handle the additional airflow.
4 PA Test
The 4 PA test is used to measure the air pressure difference between the room containing the stove and the outside environment. It’s particularly useful in homes where external vents aren’t permitted, such as listed or heritage properties. By simulating the conditions required for proper combustion, this test helps verify whether there is sufficient air supply for the safe operation of the stove, and it can also provide vital data in cases of carbon monoxide investigations.
Why Trust Bonfire?
With over 100 years combined experience, we have a full in-house team of professional chimney sweeps that perform much more than just cleaning. It’s crucial to choose a reliable and qualified service provider to carry out these important tests.
Since many of these checks are difficult for homeowners to verify, it’s essential to have confidence in the expertise of the company you hire. Bonfire ensures every safety aspect of your chimney is covered, so you can enjoy your fire with peace of mind.
Get in Contact with Us
If you have any questions or need expert advice on your chimney or fireplace, don’t hesitate to get in touch. Our friendly team at Bonfire is always ready to help with any queries or to book an inspection.
You can reach us by phone, email, or through our online contact form, and we’ll get back to you as soon as possible. Whether it’s for chimney testing, maintenance, or advice on a new installation, we’re here to assist you.
Require any of these services? Call us on 0118 970 1717 or email info@bonfire.co.uk