A log burner smokes into the room when the flue is not pulling hard enough to carry the smoke away. The most common causes are a cold flue when lighting, opening the door too quickly, wet wood, a room short of air (often because of extractor fans), and a blocked or poorly sized flue.
Warm the flue, light a hot top-down fire with the vents open, burn wood under 20% moisture and open the door slowly. If smoke leaks with the door shut or a carbon monoxide alarm sounds, stop using the stove and have it checked. Start with the table below: when the stove smokes is the best clue to why.
When does it smoke? That is the clue
| When it smokes | Most likely cause | What to do |
|---|---|---|
| Only for the first few minutes after lighting | Cold flue full of heavy air | Warm the flue first and light top-down |
| When you open the door to add logs | Door opened too fast, or fire burnt down and flue cooling | Open the air controls a minute before, then open the door slowly |
| Whenever the cooker hood or bathroom fan is on | House under negative pressure | Turn fans off to test; more air to the room |
| In windy weather, or wind from one direction | Downdraught: outlet in a pressure zone | Cowl or extra height, installer to assess |
| All the time, getting worse over weeks | Soot build-up, nest or debris | Stop using it and have it swept |
| With the door shut | Leaking door seal, flue joint or register plate | Stop using it; get it checked |
| Thick smoke from the chimney outside | Wet wood or a fire turned too low | Dry logs, hotter fire |
| Smell and haze from the stove body on first fires | New paint curing | Normal; ventilate and follow the manual |
Smoke carries carbon monoxide. Brief puffs when lighting are common. Smoke that keeps coming into the room is not. If a CO alarm sounds, open windows and doors, let the fire die, get everyone out into fresh air and get medical help if anyone feels unwell (call 999 in an emergency).
Smoke when lighting: the cold flue
Before you light, the flue is full of cold air that is heavier than the warm air in the room. A small fire cannot push it out, so the smoke rolls back into the room. This is worst on mild, still days and in chimneys on an outside wall.
Open every air control fully, hold a lit roll of newspaper or a natural firelighter under the flue outlet inside the stove for a minute until you feel it pull, then build a top-down fire: larger logs at the bottom, kindling above, firelighter on top. It gets hot fast and drives the cold air out. Our lighting guide shows the method step by step.
Smoke when the door opens
Opening the door quickly creates a puff of low pressure in the room that pulls smoke out with it. The fix is a routine: open the air controls fully, wait a minute so the fire livens up and the flue heats, then open the door a little, pause, and open it fully. Refuel when the fire has burned down to a bed of glowing embers but before it goes cold, because a cooling flue draws less.
A magnetic stove pipe thermometer helps here: it shows when the flue is in its working range, so you refuel before it drops too low.
Wood burner vents: open or closed?
For lighting and refuelling, open them. Once the fire is going well, turn the primary air (usually below the door or under the grate) down or closed for wood, because wood burns best on a bed of ash with air from above. Then use the secondary or airwash control to set the burn rate. Smokeless fuel is the opposite: it needs air from below through a grate.
Control positions vary by model, so check your manual to see which way is open; many stoves mark them with a plus and minus or with arrows. Never shut all the air off to make a load last: a starved fire smoulders, smokes and tars the flue.
Smoke from extractor fans and airtight rooms
A cooker hood, bathroom fan or tumble dryer pulls air out of the house. If the room is airtight, the chimney becomes the easiest way for replacement air to get in, and it brings the smoke with it. Test it: turn the fans off and open a window. If the smoke stops, the room needs a proper air supply.
Approved Document J sets out when a permanent air vent is needed; our guide do I need a vent for a log burner? explains the rules. Some stoves take combustion air from outside through a duct, which can help, but your installer should still check for spillage with the fans running. The Carron ECO 5kW can take an external air supply, and Opus cylindrical stoves use the Opus external air kit.
Smoke blowing back down the chimney
If it only happens in wind, the outlet is probably in a zone where wind pressure pushes down the flue: too close to a ridge, a taller building, trees or high ground. An anti-downdraught cowl helps in many cases. Where the outlet does not meet Approved Document J's position rules, extending the flue is the proper fix; see how tall should my chimney be?
Note which wind direction causes it and how strong the wind was. That record helps an installer or sweep diagnose the problem quickly.
Smoke that keeps getting worse
A flue that slowly loses its draw over weeks is often blocking up with soot, or has a nest or fallen debris in it. Stop using the stove and call a sweep. Fire and rescue services recommend sweeping a wood-burning chimney quarterly when in use, and at least once a year for smokeless fuel. Book a sweep before the season starts, because nests and debris collect over summer.
Smoke with the door closed: stop and get it checked
A stove should be sealed when the door is shut. Smoke or smell with the door closed means a leak: a flattened door rope, a cracked glass seal, a leaking flue pipe joint or a gap round the register plate. Leaking smoke carries carbon monoxide. Stop using the stove until a HETAS registered installer or sweep has found and fixed the leak, and make sure there is a working carbon monoxide alarm in the room. Building Regulations require one in the room whenever a new or replacement stove is installed.
If the CO alarm sounds: open windows and doors, let the fire die, get everyone out into fresh air and get medical help if anyone feels unwell (call 999 in an emergency). Do not use the stove again until it has been checked.
Thick smoke from the chimney pot
That is unburnt fuel, almost always from wet wood or a stove turned down so low it smoulders. It wastes heat, coats the flue in tar, annoys neighbours and, in a smoke control area, can lead to a penalty: in England, a chimney releasing smoke in a smoke control area can incur a penalty of up to £300. Burn wood under 20% moisture, ideally certified Ready to Burn, and run the stove with enough air to keep flames visible. A hot, well-set stove should show little more than a heat haze at the pot once it is up to temperature.
See our guide to the best wood to burn for how to buy, test and store logs.
Smoke from a brand new stove
New stoves are finished with heat-resistant paint that cures during the first few fires. Expect a smell and some haze from the stove body itself, not from the firebox. Follow the curing instructions in your manual, which usually mean several small fires before a full one, open the windows and keep pets and anyone with breathing problems out of the room until it stops. If smoke is coming from the door or flue joints rather than the paintwork, treat it as a leak.
If you are replacing a stove that has never drawn well, choose one sized for the room and exempt for smoke control areas, and have it installed to the right flue size. Browse smoke control exempt stoves and flue pipe.
Quick checks before you call anyone
- Wood dry? Under 20% on a freshly split face.
- Controls open fully for lighting and before opening the door?
- Flue warmed for a minute before lighting?
- Fans off and a window open as a test?
- Swept within the last season, with no nest or debris?
- Door rope sound? With the stove cold, close the door on a strip of paper; it should grip.
Common questions
Why is smoke coming out of my stove when the door is closed?
A sealed stove should not leak smoke with the door shut, so there is a leak at the door rope, glass seal, flue joint or register plate, or the flue is blocked. Stop using it and have it checked, as leaking smoke contains carbon monoxide.
Should wood burner vents be open or closed?
Open all of them for lighting and before opening the door. Once the fire is established, close the primary (bottom) air for wood and control the burn with the secondary or airwash. Check your manual for which direction is open on your model.
How do I stop smoke blowing back down my chimney?
If it happens in wind, fit an anti-downdraught cowl or extend the flue so the outlet meets the Building Regulations position rules. If it happens when fans are on, the room needs more air.
Why does my fireplace smoke into the house?
An open fireplace needs a large air supply and a warm flue. Smoke into the room usually means a cold or oversized flue, too little air in the room, or a blockage. Open a window to test, warm the flue before lighting and have the chimney swept.
Is it dangerous if my log burner smokes?
Brief puffs when lighting are common, but smoke entering the room carries carbon monoxide. If it happens regularly, with the door closed, or a CO alarm sounds, stop using the stove until it has been checked.
Is it normal for a new log burner to smoke?
Some smoke and smell from the stove body is normal for the first few fires while the paint cures. Ventilate the room and follow the curing instructions. Smoke from the door or flue joints is not normal.
Why does my log burner only smoke when it is windy?
Wind is pushing down the flue because the outlet sits in a high-pressure zone near the ridge, a taller building or trees. A cowl often helps; otherwise the flue may need extending to meet the outlet position rules.
Will a bigger stove stop the smoking?
No. An oversized stove is usually run turned down, which makes it smoulder and smoke more. Choose a stove sized for the room and run it hot enough to keep visible flames.
Still smoking?
Send us a short video of your stove and a photo of the chimney outside and we will help you narrow down the cause and what to ask your installer or sweep.
