how to tell if chimney flue is open

3 min read 30-01-2025

A blocked chimney flue is a serious issue, posing risks from carbon monoxide poisoning to chimney fires. Knowing how to check if your flue is open is crucial for home safety and efficient heating. This guide provides various methods to determine if your flue is functioning correctly.

Visual Inspection: The Simplest Check

Is the damper open? The first, and easiest, step is to check the damper. This is a valve located at the bottom of your chimney, inside the fireplace.

Open damper: You should see a clear opening leading up the chimney.
Closed damper: The opening will be blocked by the damper plate. This needs to be opened before use.

Looking up the chimney: If your damper is open, try to visually inspect the flue.

Use a flashlight: Shine a strong light up the chimney. You might be able to see obstructions. A partially blocked flue will show reduced light penetration.
Caution: Never lean over the opening to look. Use a mirror on a long stick or a chimney camera.
Professional inspection: If you can’t clearly see the top of the flue, it’s time to call a professional chimney sweep.

Testing for Airflow: The Practical Approach

The tissue test: A simple and effective method is the tissue test.

Light a match: Light a match or use a lighter.
Hold near the flue opening: Hold the lit match near the opening of the flue (with the damper open!).
Observe the flame: A strong updraft will pull the flame towards the chimney. A weak or no updraft indicates a potential blockage.
Repeat with a piece of tissue: A small piece of lightweight tissue paper held near the opening will also be drawn upward by a functioning flue.

The smoke test: Similar to the tissue test, you can use smoke.

Incense or smoke bomb: Use incense or a specialized chimney smoke bomb (available online or at hardware stores).
Observe the smoke: If the smoke is drawn up and out of the chimney freely, the flue is likely open. If it wafts back into the room, there's a problem.

Hearing the Draft: An Auditory Cue

Listen for the sound of wind: If you place your ear near the flue opening (with the damper open), you might hear a slight whooshing sound caused by wind drafts. This indicates airflow through the chimney. The absence of such a sound doesn’t definitively mean a blockage, but it warrants further investigation.

Advanced Techniques: When a Visual Inspection Isn't Enough

Chimney Camera: A chimney camera is a specialized tool that provides a detailed visual inspection of your chimney flue from the bottom. It allows chimney sweeps to identify blockages, cracks, and other issues that are not visible using a simple flashlight.

Pressure Testing: Pressure testing measures the airflow within the chimney to identify obstructions or leaks. This is a more precise method used by professionals.

What to do if your Chimney Flue is Blocked

If you determine your flue is blocked, do not attempt to clear it yourself. This can be dangerous and lead to further complications. Instead, contact a qualified chimney sweep. They have the expertise and equipment to safely clear blockages and ensure your chimney is working properly.

Regular Chimney Maintenance: Prevention is Key

Regular chimney maintenance is crucial for preventing blockages and ensuring safety. Schedule an annual inspection by a professional chimney sweep to identify and address potential issues before they become serious problems. This proactive approach helps maintain the efficient and safe operation of your fireplace and chimney.

Remember, a blocked chimney flue poses significant risks to your safety and the health of your home. By employing these methods, you can proactively check your chimney's functionality and take necessary actions to ensure a safe and comfortable winter season.