How often should a chimney be swept?

Every time you light your stove, smoke leaves a little soot and tar inside the flue. Over a season this builds up, narrowing the flue and creating fuel for a chimney fire. Regular sweeping removes it, checks the flue is clear and is one of the simplest ways to keep a stove safe.

In short

• Wood: HETAS advises at least twice a year, and NACS guidance is quarterly when in use.
• Smokeless fuel: at least once a year.
• Book a sweep before the heating season, and again after the busiest burning months if you sweep twice.
• Always sweep after a long period of disuse and when you move into a home with a stove.
• Keep the sweep's certificate, as your home insurer may ask for evidence of maintenance.

What the industry bodies recommend

There is no single legal rule for how often an owner-occupier must sweep a chimney. Instead, the main industry organisations publish guidance, and their figures differ slightly.

HETAS

HETAS, which runs the competent person scheme for solid fuel installers, advises sweeping at least twice a year when burning wood and at least once a year for smokeless fuel. It suggests sweeping just before the heating season starts and, if you sweep twice, again after the peak of the season.

NACS

The National Association of Chimney Sweeps gives guidance figures of quarterly when in use for wood and at least once a year for smokeless fuel. It stresses that the right frequency depends on the fuel, the appliance, how much you use it, the moisture content of your wood and the type of chimney, and that your sweep can advise.

Other trade guidance

The Solid Fuel Association recommends sweeping at least once a year, ideally before the heating season, and more often for wood or bituminous coal. Members of trade bodies such as the Guild of Master Chimney Sweeps can also advise on a schedule for your particular stove.

In practice, a stove used every evening through a Northumberland winter will need more attention than one lit a few weekends a year. The common thread is clear: wood needs sweeping more often than smokeless fuel.

What affects how quickly a flue gets dirty?

• Wet fuel. Burning logs above 20% moisture is the biggest cause of heavy tar deposits. Our guide to choosing the best firewood explains how to check.
• Slumbering. Turning the air right down and leaving the stove to smoulder overnight cools the flue and encourages tar.
• Flue condition. An unlined or oversized old chimney stays cooler and collects more deposits than a correctly sized insulated liner. Find out more about lining a chimney.
• Usage. More hours of burning means more soot.

Signs your chimney needs sweeping sooner

• the stove is harder to light or draws poorly,
• smoke puffs back into the room when you open the door,
• the glass blackens quickly even with dry wood,
• there is a strong smell of soot or tar when the stove is cold,
• you see soot or debris falling into the stove,
• birds have been nesting in or around the chimney pot.

If you notice any of these, book a sweep before using the stove heavily again. If your carbon monoxide alarm ever sounds, stop using the stove and get it checked. See our guide on carbon monoxide alarms.

What does a sweep do?

A professional sweep will protect the room, sweep the flue with brushes or rotary equipment, remove soot from the stove and smoke chamber, and check the flue is clear. Many will also carry out a smoke draw test and point out problems such as damaged rope seals, a cracked baffle or a defective cowl. Afterwards you should receive a certificate recording the appliance, the flue and the work done.

Chimney sweeping and home insurance

Many home insurance policies include conditions about maintaining chimneys and solid fuel appliances, and some require sweeping by a professional at a stated frequency. If you make a claim after a chimney fire, your insurer may ask for evidence that the chimney was maintained. Terms vary widely between insurers, so read your own policy wording or ask your insurer directly rather than relying on general advice.

It is also worth telling your insurer if you have a new stove fitted, and keeping both the installation certificate and your sweep certificates together.

Can I sweep my own chimney?

Legally you can, but it is hard to do thoroughly, you will not get an independent certificate, and you may miss defects a trained sweep would spot. If your policy requires a professional sweep, doing it yourself may not meet that condition.

Moving into a home with a stove

If you have just bought or rented a property with a wood burner, NACS advises having the chimney swept as soon as possible, because you cannot be sure when it was last done. While you are at it:

• ask the seller or agent for the installation certificate from a competent person scheme or Building Control,
• check there is a working carbon monoxide alarm in the room,
• look for the notice plate that records the flue and appliance details,
• find out what fuel the stove is designed for, and whether you are in a smoke control area.

If no paperwork exists, or the sweep raises concerns about the flue, it is worth having the installation checked before you rely on it through the winter.

Getting a flue that is easier to maintain

If your stove draws poorly or the flue needs sweeping unusually often, the underlying problem may be the chimney itself, the stove or how it was installed. A survey can identify whether relining or replacing an older stove would help. Get in touch to arrange a visit and a written quote.