The short answer: once a year is the floor, not the target

If you burn wood on a stove, you should have the chimney swept at least once a year — and that is genuinely the minimum rather than a comfortable target. For a stove lit most evenings from October to March, twice a year is far more realistic, and many sweeps suggest one clean at the end of the burning season and another before you start again in autumn.

The reason is simple. Burning wood produces soot, and it also produces creosote — a sticky, tar-like deposit that condenses on the cooler upper parts of the flue. A thin film of it is normal. A thick layer is fuel sitting inside your chimney, waiting for hot enough flue gases to ignite it. Chimney fires are not rare, and they are almost always the result of a flue that has gone too long without attention.

What actually changes the timetable

No single answer fits every house, because four things shift the schedule: what you burn, how often you burn it, how you burn it, and what sort of flue you have.

• Seasoned wood: sweep at least twice a year when the stove is in regular use, and more often if you burn daily.
• Smokeless fuel: once a year is usually adequate.
• Bituminous coal: twice a year, as it leaves heavier deposits.
• Gas and oil: once a year, by a qualified engineer.
• Open fires: at least once a year, twice if the fire is your main source of heat.

Overnight burning is the factor most people underestimate. Shutting the stove down and letting it smoulder for eight hours produces cooler, smokier flue gases, and cool gases deposit far more creosote than hot ones. If you bank the stove up every night through winter, treat twice-yearly sweeping as an absolute floor and consider a mid-season check.

Warning signs the flue is overdue

• A sooty or acrid smell in the room, particularly on mild or damp days when the flue is idle.
• Smoke spilling back into the room when you open the door or add fuel.
• Glass blackening faster than usual, or the fire struggling to establish.
• Flakes of soot or tar appearing on the stove top, register plate or hearth.
• A weaker, duller draught than you remember from last winter.
• Scratching or flapping sounds from the chimney — birds nesting in an unused flue is common in spring.

Any one of these is a reason to book a sweep rather than wait. If you suspect a chimney fire — a low roaring sound, a vibrating stove, a hot flue pipe or burning debris outside — get everyone out, call the fire service, and have the chimney inspected before you light it again.

What a proper sweep actually involves

A good sweep is not just a brush on a rod. Expect the chimney to be cleaned from the appliance upwards and, where safe access allows, from the top down, with dust sheets laid and a vacuum running to keep the room clean.

• Removing soot and tar from the flue, the bends, the register plate and the stove's baffle.
• Checking the flue for cracks, missing mortar, damaged liners and correct termination above the roof.
• Checking the cowl or terminal and clearing any nest or debris.
• A smoke test to confirm the flue is sound and pulling correctly.
• Checking ventilation and confirming your carbon monoxide alarm is present and in date.
• Issuing a certificate or record card showing the date and the work carried out.

Habits that keep the flue cleaner for longer

Sweeping frequency is partly in your hands. Burn well and deposits build slowly; burn badly and you will be paying for a sweep every few months.

• Use wood with a moisture content below 20 per cent. A cheap moisture meter pays for itself in a season.
• Never burn unseasoned, painted, treated or pallet wood, and never household rubbish.
• Run the stove hot for a while each day rather than keeping it permanently slumbering.
• Keep the air supply open enough for visible flames; smoke means incomplete combustion and more deposit.
• Only burn coal or smokeless fuel in an appliance designed for it.

When to book, and why the paperwork matters

Late summer is the sweet spot. Sweeps get booked solid from the first cold snap in October, and the last thing you want is a flue untouched since March when the frost arrives. If you burn heavily, add a second appointment in spring, once the stove has gone out for the year.

Keep the certificate. Many home insurance policies require you to maintain the chimney, and some will ask for proof of sweeping if you need to claim. A recent certificate is also a quietly reassuring document if you ever sell. And if you have moved into a house with a stove you have never used, or one that has sat idle for a couple of years, have it swept and inspected before the first fire — not after.