Sweep Sisters carrying out a chimney smoke test on a wood burning stove
HETAS-certified sweeps across Essex, Herts & North & East London

Chimney Smoke Testing

A chimney smoke test shows whether your flue pulls smoke up and out of the house, and whether any of it is escaping through cracks into your rooms, loft or next door. Every sweep we do ends with one. Rated 5.0 from 105 Google reviews.

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What a smoke test is

A simple test that tells you if your chimney is safe to use

A chimney smoke test does two jobs. First, it proves the flue draws: smoke released at the fireplace or stove should be pulled straight up the chimney and out of the pot. Second, it checks the flue is sound: with the top sealed off, smoke is pushed through the whole length of the chimney, and anywhere it seeps out shows a crack, gap or open joint.

We are Adele and Sian, sisters and HETAS-certified sweeps based in Harlow, and we do every test ourselves. We use smoke pellets that give off a thick, harmless white smoke, so even a small leak is easy to spot. We check the room the fire is in, the rooms above, the loft and, on terraced and semi-detached houses, any shared chimney breast.

A smoke test comes as standard with every chimney sweep we carry out, and the result goes on your sweeping certificate. If you only need the test on its own, for example before buying a house or relighting an old fireplace, just ask when you book.

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What a chimney smoke test checks

A smoke test is quick, but it answers the questions that matter most before you light a fire.

Draw and flow

We watch how quickly the smoke is pulled up the flue. A healthy chimney takes it away cleanly. Smoke that lingers, curls back into the room or rolls out of the fireplace points to a blockage, a cold flue or a draught problem.

Leaks through the flue

With the pot sealed, smoke fills the flue under light pressure. Any crack in a clay liner, gap in the mortar or split in a steel liner lets smoke out, and that is exactly where fumes would escape when the fire is lit.

Rooms, loft and next door

We walk the house while the test runs: bedrooms above, the loft space and the chimney breast on every floor. On a shared stack we can ask you to check with your neighbour, because a leak can show up on their side of the wall.

When you need a chimney smoke test

You get one with every sweep. These are the times it is worth booking one even if the chimney was swept recently.

  • As part of every annual sweep
  • When you're buying a house with a fireplace or stove
  • Before relighting a fireplace that hasn't been used for years
  • After a chimney fire, before the fire is used again
  • Before a new stove goes into an existing chimney
  • Landlords checking a rental before new tenants move in
  • You can smell smoke in an upstairs room or the loft
  • Your neighbour can smell smoke when your fire is lit

Stove installers carry out their own smoke test when they commission a new appliance, but a chimney that's going to take a stove should be swept and tested first so any problems are found before the money is spent. After a chimney fire, don't light anything until the flue has been checked. Read our guide to the signs of a chimney fire if you're not sure whether you've had one, and our advice on carbon monoxide and log burners.

How we smoke test a chimney

This is how we carry out the test in your home. Dust sheets go down first and stay down until we've packed up.

  1. We sweep and look over the flue

    A smoke test is most reliable on a clean flue, so it normally follows the sweep. We check the fireplace or stove, the register plate and anything we can see of the flue before we start.

  2. We warm the flue and test the draw

    We light a smoke pellet in the grate or stove with the chimney open and watch the smoke. It should be drawn up steadily and leave through the pot. If it hangs about or spills back into the room, we look for the reason.

  3. We seal the top and fill the flue

    Next the pot or outlet is closed off and more pellets are lit. The flue fills with smoke, and while it does we check every room the chimney passes through, the loft, the stack and the outside walls for any smoke coming through.

  4. We explain the result and write it down

    We tell you straight away whether the chimney passed or failed and what we saw. The result goes on your certificate, along with any notes or recommendations.

How long does it take? The smoke test doesn’t take long and is done as part of the visit. On a bigger house, or one with several floors above the fireplace, it can take a little longer because we check each room in turn.

Pass or fail: what the result means

Plenty of chimneys pass first time, but older flues can show leaks. When a chimney fails, we tell you why and what to do next.

A pass

  • Smoke is drawn up the flue quickly and steadily
  • Smoke leaves only through the pot or terminal
  • No smoke in other rooms, the loft or next door
  • Recorded on your certificate, ready to use

A fail

  • Smoke seeping through the chimney breast or ceiling
  • Smoke in the loft, an upstairs room or a neighbour's house
  • Smoke escaping from the stack below the pot
  • Poor draw, with smoke spilling back into the room

If your chimney fails a smoke test

A failed test means the chimney shouldn't be used until the cause is found and put right. The usual culprits are a cracked or broken clay liner, an old flue that was never lined, open mortar joints, gaps where the chimney breast has been altered or partly removed, or a damaged steel liner on a stove. Poor draw can also come from a blockage such as a nest, or from a pot or cowl that isn't suited to the chimney.

The next step is usually a CCTV chimney inspection, which lets us see inside the flue and pinpoint where the leak is. From there we can quote for chimney repairs such as repointing or a new pot, or recommend a capping if the chimney isn't going to be used again. Where a flue needs relining, that is work for a HETAS-registered installer, and we'll tell you what to ask for. Nothing is done without a quote and your go-ahead first.

What our customers say

Reviews from homeowners across Essex, Hertfordshire and North & East London.

Google5.0★★★★★105 Google reviews
  • ★★★★★Google
    They are great. Turned up on time. Done a great job ,very clean. Cleaned my burner up lovely, fixed my rope on my door. Can’t recommend then enough. Definitely will be using the every year from now on
    Luke G.November 2026 · Google review
  • ★★★★★Google
    Recently moved into a property with a log burner, having not experienced the need for getting one cleaned I booked sweep sisters through recommendation and they were spot on! For my house insurance I needed an accredited sweeper which they are. Adele and Sian were so friendly and took care of my home when cleaning and left the room spotless! Spoke through what they had done, would highly recommend, you will not be disappointed!!
    Nicola D.October 2026 · Google review
  • ★★★★★Google
    Sweep Sisters always provide an excellent and professional service. We have used them for the past 3 years and we would fully recommend them to sweep your chimney.
    Donna C.October 2026 · Google review
  • ★★★★★Google
    Having been let down by someone else, we looked at reviews and thought we would try the Sweep Sisters. Great decision. So professional and friendly, quick and super clean job. Very knowledgeable, no one else will be sweeping our chimney going forward.
    Chris A.October 2026 · Google review
  • ★★★★★Google
    Adele came round today (Saturday) to sweep a couple of our chimney stacks, and the service was fantastic from start to finish. She was extremely knowledgeable, professional, tidy and clean, keeping dust to an absolute minimum and making sure everything was properly covered. The CO alarm and smoke evacuation tests were included in the price, and she cleaned the stoves too. I honestly couldn’t recommend her highly enough. We’ll definitely be using Adele for our annual chimney sweeps going forward and wouldn’t consider using anyone else. Fantastic service all round. Highly recommended.
    Paul C.October 2026 · Google review
  • ★★★★★Google
    It was a pleasure to have The Sweep Sisters in my home today. They let me know in advance when to expect them and arrived on time at my door with friendly smiles. Their work on my log burner and chimney was thorough and efficient. No fuss and no mess. I would be happy to recommend them.
    Linda W.October 2026 · Google review
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Chimney smoke test cost

There's no separate charge for the smoke test when we sweep your chimney. It's part of the job.

Sweep with smoke test

From £95

Full sweep, visual inspection, smoke test, clean-up and a sweeping certificate.

CCTV flue inspection

From £75

Added to a sweep. A camera survey of the whole flue, with photos of anything that needs attention.

Sweep and CCTV together

From £170

The best starting point for a new home, or a flue that hasn't been used for a while.

Repairs

Quoted

If the test finds a problem, we explain it and quote before any work starts.

Prices are for a single flue. No hidden call-out fees. Got a question? Get in touch.

Smoke testing across Essex, Hertfordshire and North & East London

We're based in Harlow and smoke test chimneys as a routine part of every sweep. Not sure if we cover your postcode? Send us a message.

Essex

Hertfordshire

North & East London

Chimney smoke test questions

What is a chimney smoke test?

It's a check that your chimney draws properly and doesn't leak. We light smoke pellets at the fireplace or stove, watch the smoke go up and out, then seal the top of the flue and look for smoke escaping into rooms, the loft or next door.

Is a smoke test included with a chimney sweep?

Yes. Every sweep we carry out ends with a smoke test, and the result is recorded on your sweeping certificate. Our standard sweep starts from £95.

How long does a chimney smoke test take?

It doesn't take long and is done as part of the visit. Larger houses take a little longer because we check every room and floor the chimney runs through.

Can I smoke test my own chimney?

You can buy smoke pellets, but knowing where to look and what a small leak means takes experience. A test done by a HETAS-certified sweep is also recorded on a certificate, which is what insurers, landlords and buyers want to see.

Do I need a smoke test before buying a house?

If the house has a fireplace or stove you plan to use, it's well worth it. A sweep and smoke test tells you whether the chimney is safe to use, and a CCTV inspection can be added if you want to see the condition of the liner.

What happens if my chimney fails?

Don't use the fire until it's sorted. We explain what we saw, usually recommend a CCTV inspection to find the exact cause, and quote for any repairs before work starts. Relining is done by a HETAS-registered installer.

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Book a chimney smoke test

Tell us your town, what you burn and when suits you, and we will confirm a date and price.

Prefer to talk? Call 0330 133 2121 or email contact@sweepsisters.co.uk.