Quick answer: Why is my fireplace smoking? Usually because the chimney isn’t drawing. The usual causes are a closed damper, a cold flue, a blockage such as a bird’s nest or creosote, wet firewood, wind, or a house competing for air. A puff at lighting is normal. Smoke that keeps coming back means the flue needs checking. If anyone feels headachy, dizzy or sick while the fire is going, get everyone out and call 000 in an emergency.
Written by Ofek Shamir, owner of The Guys Group · Updated 29 September 2026 · Sources: Australian Home Heating Association, Fire and Rescue NSW, NSW Health and other sources linked below.
Is smoke from my fireplace dangerous?
Yes, it can be. Wood smoke contains fine particles and carbon monoxide (CO), a gas you cannot see or smell. If anyone in the house has a headache, nausea, dizziness, weakness, tiredness or confusion while the fire is going, open the doors and windows if you can do it quickly, leave the house, and seek medical advice. In an emergency, call 000.
NSW Health lists headache, nausea, vomiting and weakness as common symptoms of carbon monoxide poisoning. The Better Health Channel notes that a badly vented or leaking wood heater can raise CO levels indoors, and that drowsiness can be a warning sign. As a precaution, consider fitting a carbon monoxide alarm in the room with the fireplace or heater.
Why does my fireplace only smoke when I first light it?
A little smoke at start-up is normal while the flue warms. The Australian Home Heating Association (AHHA) says you can expect some smoke from the flue when you first start a fire, but it should not last longer than about 10 to 15 minutes. Smoke that keeps spilling out after that points to a drawing problem.
What should I check first when my fireplace smokes?
Work through these in order:
- Check the damper. Make sure it is fully open before you light anything.
- Warm the flue (open fireplaces only). See the newspaper method below.
- Check the firewood. It should be under 20% moisture.
- Open a nearby window slightly and turn off exhaust fans. If the smoke clears, the house is competing with the fire for air.
- Note the weather. Smoke only on windy days points to downdraught.
- If none of that helps, stop using the fire and have the chimney inspected and swept.
What is my smoky fireplace telling me?
| What you notice | Likely cause | What to try | When to call a sweep |
|---|---|---|---|
| A puff of smoke when lighting, then it clears | Cold flue | Warm the flue first | If it lasts beyond 15 minutes |
| Smoke pours out from the start, every time | Closed damper or blocked flue | Check the damper is fully open | Now, if the damper is open |
| Fire smoulders, hisses, little flame | Wet or unseasoned wood, not enough air | Wood under 20% moisture, air open | If it smokes with dry wood too |
| Smoke stops when a window is opened | House competing for air (negative pressure) | Crack a window, fans off | If it keeps coming back |
| Only smokes on windy days | Wind downdraught | Note whether it only happens in wind | To check the cowl and flue height |
| Smoke puffs out when the heater door opens | Door opened too fast, low draw | Open the door slowly | If it still happens |
| Birds in the chimney, debris in the firebox | Nest or debris blockage | Do not light the fire | Before you light it again |
Is the damper open?
A damper that is closed or only partly open is a common reason a fireplace smokes, and the easiest to fix. The damper is a metal plate in the throat of the chimney, just above the firebox. If it is not fully open, smoke has nowhere to go but back into the room. Open it fully before you light anything. If it will not open all the way, a sweep can check it during a clean.
How do I warm up a cold flue?
On an open fireplace, roll up a sheet of newspaper, light one end and hold it inside the firebox near the throat of the flue, with the damper open, for 30 to 60 seconds until the smoke starts pulling upwards. Then light the fire as normal. A cold flue holds cold air that acts like a plug, pushing smoke back out.
This tip is for open fireplaces only. For a slow combustion heater, follow the manufacturer’s instructions; the AHHA’s lighting method uses firelighters and kindling, not newspaper.
If you suspect a bird’s nest or other blockage, do not light anything. Dry nesting material catches easily and can start a chimney fire, so have it cleared first.
How dry should my firewood be?
Firewood should be under 20% moisture. The AHHA recommends a range of 12 to 20% and says wet wood wastes the fire’s energy boiling off water instead of heating the room. Damp wood smoulders, makes far more smoke and leaves more creosote in the flue.
- Store wood under cover in a dry, ventilated spot, stacked so air can move through it.
- The AHHA suggests storing wood for at least 12 months after you buy it, and buying in spring or summer for the following winter.
- The only reliable check is a moisture meter reading taken from the inner core of a freshly split piece.
- Never burn treated or painted wood.
How long should the air controls stay open on my slow combustion heater?
When you light a slow combustion heater, leave the air controls fully open for at least 30 to 45 minutes. After each reload, give it full air for 15 to 20 minutes before turning it down. That is the AHHA’s guidance. Turning the air down too early starves the fire, so it smoulders, smokes and builds creosote in the flue.
Why does my slow combustion heater smoke when I open the door?
Opening the door quickly lets room air rush in and pushes smoke out before the flue can carry it away. Unlatch the door and leave it slightly ajar for a few seconds, then open it fully. It also helps to turn off nearby exhaust fans, which pull air out of the house and can draw smoke back through the heater. If smoke still spills out with the door opened slowly, the flue may be restricted and is worth having swept.
Is something blocking my chimney?
If the damper is open, the flue is warm and the wood is dry but the fire still smokes, something in the chimney is probably restricting the airflow:
- Birds’ nests. A nest can block a flue almost completely.
- Leaves and debris collected around the cowl or cap at the top.
- Creosote. The tarry layer left by smoke narrows the flue over time and, combined with soot, can catch fire. See the signs of creosote build-up in a chimney.
The AHHA advises cleaning a flue or chimney at least once a year, and more often if you use your heater almost every day. It warns that a neglected flue can cause backdrafts, meaning gusts of smoke or combustion gases entering your home. Fire and Rescue NSW also says to “Ensure flues and chimneys are regularly cleaned.” See how often you should sweep a chimney in Sydney.
Why does my fireplace smoke when it’s windy?
Wind blowing across the top of a chimney can create a high-pressure zone that forces air back down the flue. It is more likely when the chimney top sits close to a higher roof ridge or a taller building.
For wood heater flues, the AHHA summarises the Australian and New Zealand installation standard as a flue at least 4.6 metres from hearth to flue cap. If the flue is within 3 metres of the roof ridge, it must sit at least 600 mm above it. A cowl on the flue top is designed to deflect wind and keep the draw going upwards. A sweep can check the cowl and flue top during a clean.
Why does it smoke when the rangehood or exhaust fan is on?
In a well-sealed home, a running rangehood or bathroom exhaust fan pulls air out of the house and lowers the indoor pressure. The easiest path for replacement air then becomes the chimney, and the smoke comes down with it.
Test it by opening a window near the fire slightly while it is struggling. If the smoke clears and the fire picks up, the house is competing with the fire for air.
Is my fireplace too big for its chimney?
Sometimes the opening is simply too large for the flue to handle. As a rule of thumb, a flue’s cross-section should be no less than one-tenth the area of the fireplace opening. A flue that is too small cannot exhaust the smoke properly, so the fire smokes even when everything else checks out. A sweep can measure the opening and the flue and tell you whether the proportions are likely to be the problem.
When should I stop using the fire and call a sweep?
Stop using the fire straight away, and do not relight it until the chimney has been checked, if:
- you hear a loud roaring or rumbling from the chimney, or see sparks or flames coming out of the top. That can be a chimney fire: get everyone out of the house. Fire and Rescue NSW’s advice is that once you get out, “stay out and dial Triple Zero (000)”.
- anyone has a headache, dizziness, nausea or drowsiness while the fire is going (leave the house and call 000 in an emergency)
- smoke keeps pouring into the room after the first 10 to 15 minutes
- you have heard birds in the chimney or found nesting material or debris in the firebox
- you notice a strong tarry smell or black, flaky build-up in the firebox
Book a sweep soon, even if the fire seems fine, when:
- the smoke keeps coming back after you have checked the damper, warmed the flue and used dry wood
- the chimney has not been swept in the past 12 months
See what is included in a professional chimney sweep, or our fireplace cleaning in Sydney.
Book a chimney sweep in Sydney
The Chimney Guys Sydney sweep open fireplaces and slow combustion heaters across Sydney. A sweep clears the flue, checks for nests and debris, looks at the damper and cowl, and tells you whether a drawing problem is a blockage or something structural. Chimney sweeps start from $349 + GST. See our chimney sweep service.
Sources
- Tips and FAQs, Australian Home Heating Association
- Fuelling your fire, Australian Home Heating Association
- How to choose and treat firewood, Australian Home Heating Association
- Cleaning your flue, who knew?, Australian Home Heating Association
- Everything you need to know about flue systems, Australian Home Heating Association
- Heaters and open fires, Fire and Rescue NSW
- Home fire safety checklist, Fire and Rescue NSW
- Carbon monoxide poisoning, NSW Health
- Carbon monoxide poisoning in the home, Victorian Department of Health
- Wood fires and breathing problems, Better Health Channel
- Why does my wood burner smoke when I open the door?, The Sweeping Company
- Chimney math: fireplace and flue size correlation, Environmental Chimney Service
