How do you know if your chimney needs sweeping?

A chimney needs sweeping when the fire tells you so: smoke drifting back into the room, a fire that is slow to catch or burns lazily, a sharp tarry smell when the stove is cold, black flakes or oily deposits in the firebox, and soot on the hearth in the morning. Any of those means a sweep before the next fire. And if the next fire is the first of the season, book it anyway: what matters is what is in the flue now, not how often you lit it last year.

What are the signs to look for?

• Smoke coming back into the room. The flue is not carrying the gases away. If it happens every time, the flue is narrowed or partly blocked. If it only happens at lighting and clears once the fire is going, the flue is cold and slow to pull, which is a warm-up problem more than a deposit problem, but have it checked anyway. Either way, smoke in the room means combustion gases in the room, and carbon monoxide comes with them with no smell and no colour, so stop using the fire until the flue has been checked and keep a carbon monoxide alarm in the room with the appliance.
• A fire that will not draw. Slow to catch, lazy flames, a stove that only burns with the door cracked open. The flue is narrowed by deposit, or there is a nest.
• A sharp, tarry smell when the stove is cold. Damp air pulls the smell of creosote down the flue and into the room, worst after rain. A faint woodsmoke smell is normal; a sharp tar smell means there is deposit to sweep.
• Black flakes or oily, shiny deposits in the firebox or on the baffle plate of a stove. That is creosote coming off the flue walls above, which means there is more of it still up there.
• Soot fall. A small pile in the firebox or on the hearth overnight, with no fire lit.
• Birds. Scratching or chirping in the chimney breast in spring, twigs or droppings in the firebox. A nest is a full blockage, and the flue is not to be lit until it is out.

How do you check the flue yourself?

This part is safe to do from the hearth. The roof is not part of it.

1. Wait until the stove or fireplace is completely cold, a full day after the last fire.
2. Open every air control and the damper so the flue is open end to end. On a stove, lift out the baffle plate if the manual shows it lifts out, so you can see straight up the flue. On an open fireplace, lay a dust sheet and look up from the hearth.
3. Put on glasses and a mask. Whatever is loose falls the moment the wall is touched.
4. Shine a strong torch up the flue. On a straight flue you should see daylight at the top. A dark mass where the daylight should be is a nest or a heavy deposit.
5. A mirror held at an angle, or a phone camera with the flash on, shows the first metre of the flue wall, which is where a hard layer often sits. A clean first metre does not prove the rest of the flue is clear, because a nest and the worst of the glaze both sit higher up and out of sight.
6. Scrape a coin along the wall just above the throat and look at what comes off. That tells you which stage the deposit is at, and the stage decides whether a brush is enough.
7. Leave the cowl and the pot to the sweep. Look at them from the ground with binoculars if you like; do not go up for them.

What does creosote look like at each stage?

• Stage one. Light, dusty, matt black soot that comes off the wall with a fingertip and falls as powder. Normal after a season of hot, dry fires. A brush removes it.
• Stage two. Crunchy, glossy black flakes, like burnt toffee, that come away in chips when scraped. It takes a stiff brush and real effort, and it is the point where a home kit starts to fail.
• Stage three. A hard, glazed, shiny coating, sometimes with runs down the wall like tar, so the flue looks wet or enamelled. No brush moves it. It is the most flammable form, it needs a chemical treatment or a rotary tool, and it usually means the flue has been burning cool for years.

Does a chimney used one week a year still need sweeping?

Yes. The rule of thumb is a sweep once a season for any fireplace or stove lit through the winter, done before the first fire rather than after the first problem, and more often if the stove runs most days. A flue lit only two or three times a year may have little in it to brush out, and it is still opened up and looked at every year, because a nest or a cracked liner does not care how often the fire is lit. The holiday home that burns for a week at Christmas is argued out of it on the grounds that a week of fires cannot lay down a season of soot. That is true, and it misses the point: the danger is not the deposit you are about to make, it is what is already in the flue when you strike the match.

A chimney that has stood open through spring and summer is the one most likely to hold a nest, and last year’s deposit has spent months in damp air turning acidic and hard. A week of hard burning in a flue nobody has looked up since last winter is exactly the week chimney fires happen. Before the first fire, a sweep is a check as much as a clean.

The timing is more predictable than the mild reputation suggests. At Faro’s airport station the mean daily minimum drops from 15.8 °C in October to 11.9 in November and 9.7 in December, which is also the wettest month of the year at 90.0 mm of rain (IPMA, Normais Climatológicas 1991-2020, Faro station). That station sits on the coast. By the time the first fires get lit, the flue has stood open to the autumn rain for weeks, so October is the month to look up it.

Why do burning habits matter?

Two flues the same age can be in completely different condition, and the difference is almost always how they were burned.

• Damp wood. Water boils off, cools the flue gases, and the tar in the smoke condenses on the flue wall instead of leaving the top. Firewood should be seasoned and dry; a cheap moisture meter reading below about 20 per cent is the test.
• Resinous wood. The pine and eucalyptus sold by the trailer here burn hot and fast and leave more tar than a dense hardwood such as olive.
• Slumbering the stove overnight. Shutting the air down to keep embers till morning makes a cool, smoky, starved fire, and the flue is too cool to carry the tar out. This single habit builds stage three creosote faster than anything else. Burn hot, then let it go out.
• A cold flue. An unlined masonry flue on an outside wall cools the gases faster than a lined one, so it needs sweeping more often for the same use.
• Treated or painted timber and household rubbish. Never. The fumes are toxic and the residue corrodes a liner.

What does a sweep do that a brush kit does not?

• Matches the rods and the brush to the flue: the right diameter, and nylon for a steel liner, since wire scores it.
• Seals the opening and runs a vacuum at the base, so the room stays clean.
• Works from both ends when the flue bends, with proper access to the roof.
• Uses a rotary tool or a chemical treatment on stage two and three deposit.
• Clears a nest in one piece rather than pushing it tighter into the flue.
• Checks the cowl for rust, bird damage or a winter storm, the pot for cracks, the joint between stove and flue, and the liner, with a camera when the history calls for it.
• Tells you plainly what condition the flue is in, in writing if you ask.

If the torch shows stage two or three deposit, a dark mass, or you simply do not want soot in the living room, this is the point to hand it over. Handyman Algarve arranges a chimney sweep in the Algarve with a free quote before the visit, and the professional assigned to your job brings the sheeting, the vacuum and rods sized to the flue. How the visit is priced is set out in how a chimney sweep is priced.

Where does DIY stop?

A chimney fire. A roar or rumble from the chimney breast, dense smoke or sparks from the pot, a chimney breast too hot to touch. Call 112 straight away, then, if it is safe to do it, shut the stove door and every air control to starve the fire, and get everyone out of the house. Never throw water on it. Whether it went out on its own or not, the flue gets a camera inspection before the next fire, because a fire hot enough to burn creosote is hot enough to crack a liner.

A cracked liner or flue. A smoke smell upstairs or in the loft, staining on the chimney breast, tar bleeding through the render of the stack, or pieces of liner in the firebox. Brushing does nothing for this. A cracked flue next to roof timbers is the route by which a chimney fire becomes a house fire, and the fix is a reline, which is a different trade from a sweep.

A nest above a bend, or a full blockage. Rods from below pack it tighter. It has to come out from above with the right access, and working on a pitched tile roof is not a job for a ladder and a good day.

Glazed creosote. A brush skids over it. It needs a chemical modifier over several fires or a rotary chain, and either way the liner underneath needs to be seen once it is off.