A flue does not block overnight. It closes in a few millimetres at a time across several years, which is exactly why almost nobody thinks to have one looked at until the fire has already stopped drawing properly.
Every winter we get calls that start the same way. The fire is harder to light than it used to be. It smokes when the door opens. It burns through more wood for less heat. The owner assumes the heater is getting old and starts pricing up a new one.
Most of the time the heater is fine. The flue is full.
That is the part nobody explains when a wood fireplace is sold. The appliance is the bit you look at, but the flue is the bit doing the work, and it is the only part of the system that quietly gets worse every single time you light a fire.
The short version
- Burning wood leaves deposits inside the flue. They are flammable, and they narrow the opening the smoke has to escape through.
- A restricted flue makes the fire harder to light, smokier and less efficient, long before it becomes dangerous.
- Fire and Rescue NSW lists keeping flues and chimneys regularly cleaned among its home heating safety measures.
- Once a year is the accepted interval, ideally before winter starts.
- Want yours looked at? Call Coffs Gas Company on (02) 6652 2411.
What is actually building up in there
When wood burns, it does not burn completely. Smoke leaving the firebox carries unburnt gases, moisture and fine particles, and as that smoke travels up a cooler flue, some of it condenses onto the walls. That deposit is creosote.
It does not all look the same. Early on it is a dry, dusty soot that brushes off easily. Left longer it turns into a sticky tar. Left longer again it hardens into a black, shiny glaze that has to be worked off mechanically. All three burn, and the glazed version burns hottest.
How fast it forms is mostly about how you run the fire. The South Australian EPA puts a number on it: “Low burning and smouldering can produce up to 10 times more smoke than a brightly burning fire.” More smoke means more deposit. A heater that is loaded up and shut down overnight will coat a flue far faster than one run hot and clean, which is why two identical heaters on the same street can be in completely different condition after five years.
Why damp wood is the expensive mistake
Unseasoned wood spends the first part of every burn boiling off water instead of making heat. The firebox runs cooler, the smoke runs cooler, and more of it sticks on the way up. You pay for it twice, once in the heat you did not get and again in the flue clean you now need sooner.
Seasoned hardwood is the single cheapest improvement most people can make to how their fire runs. There is more on fuel and firebox condition in our guide to what a wood heater is made of and what fails first.
Year one, year three, year five: what neglect actually looks like
The reason flue cleaning gets skipped is that the first year of neglect has no symptoms at all. Here is the progression as we usually see it.
The first season
A light coating forms. The fire behaves normally, nothing looks different from the room, and no reasonable person would suspect a problem. This is the season in which a clean is cheapest and quickest, and the season in which almost nobody books one.
Two to three seasons in
The coating thickens and starts to narrow the flue. The draw drops, which means the fire pulls less air, which means it burns cooler, which means it deposits faster. That is the loop that catches people out. It is not linear, it accelerates.
This is the stage where owners start adjusting their habits without noticing. Leaving the door ajar to get it going. Using more kindling. Running the air control wide open longer than they used to. The fire is telling them something and it reads as a quirk.
Four to five seasons and beyond
Now it shows. The heater becomes difficult to start, and smoke pushes back into the room when the door is opened. The NSW EPA names the underlying cause: “Check the flue, chimney and baffle regularly for a build-up of soot or creosote (a tar-like oily deposit). This build up indicates that the fire is not burning properly, and can cause chimney fires.” Glass blackens overnight. The room smells on humid days, because the deposits absorb moisture. Wood consumption climbs.
By this point the damage is not confined to the flue. Sustained cool, smoky operation is hard on baffles, seals and glass, and a fire that has been run with the door cracked open for years has usually pulled its door seals out of shape. The flue cleaning is still the cheap part. The wear that comes with it is not.
The signs, and what each one usually means
Most people can work out roughly where they sit from the way the fire behaves. This is the shortlist we run through on the phone.
| What you notice | What it usually means | What it needs |
|---|---|---|
| Fire is harder to get going than it used to be | Deposits have narrowed the flue and the draw has dropped | Inspection and clean |
| Smoke comes into the room when you open the door | Restricted flue, blocked cowl, or a nest above the roofline | Clean, plus a look at the rain cap |
| Glass blackens within a night or two of cleaning it | The fire is burning cool and smoky, which is also feeding the build-up | Clean, and a review of wood and air settings |
| Smell from the fireplace on humid days, even in summer | Deposits in the flue drawing in moisture | Clean at the end of the season rather than the start |
| Rust marks or debris in the firebox after heavy rain | Rain cap or flue components deteriorating, common near the coast | Inspection, and usually a cap replacement |
| Roaring or crackling from inside the flue, sparks from the cowl | Possible fire in the flue right now | Get everyone out and call 000 |
None of the first five are emergencies. All of them are reasons to book. The last one is not a booking, it is a phone call to the fire brigade.
What a flue fire actually is, and why you may have already had one
A flue fire is the deposit itself igniting inside the flue. It burns extremely hot, and the two things it threatens are the flue system, which can distort or fail, and the roof structure it passes through.
The part people find surprising is that a small one can come and go without anybody realising. A short, hot burn that runs out of fuel and goes out on its own leaves signs rather than damage you would notice from the lounge room: a distorted or discoloured rain cap, sections of flue that have changed colour, deposits that look puffy or rainbow-streaked rather than flat black. We find that evidence on flues whose owners are certain nothing has ever happened.
That is the argument for having a flue looked at even when the fire seems fine. An inspection tells you whether the system has already been through something, and a flue that has had a fire in it needs assessing rather than just sweeping.
The three things that actually block a flue
Creosote is the one everybody has heard of, and it is the most common. It is not the only one.
Nests and debris from above
A flue is a warm, sheltered vertical shaft with a view. Birds treat it accordingly, usually over spring and summer while the fire is not in use. A nest sitting on top of a cowl can restrict a flue that is otherwise perfectly clean, and it explains a lot of the fires that will not draw on the first cold night of the year.
The rain cap, which is where the coast gets you
The flue itself is stainless and generally outlasts everything around it. The cap on top is the part that goes, and salt air accelerates it. We see far more rusted-out caps closer to the water than we do up around Dorrigo. A failing cap lets rain and rust into the system, and the debris ends up sitting in the top of the flue.
Damage inside the system
Joins that have moved, a damaged liner in a masonry chimney, or a baffle that has warped and shifted position all change the way a flue draws. This is the category that a clean alone will not fix.
A flue clean and a service are two different jobs
These get used interchangeably and they are not the same thing, which causes genuine confusion about what has actually been done.
A chimney cleaning deals with the flue system. Rotary brushes and vacuums to take the deposits out, then an inspection of the flue, the joins and the cap. That is what protects against a flue fire and restores the draw.
A service deals with the appliance. Door and glass seals, firebricks, the baffle plate, the fan if it has one, and the general condition of the firebox. That is what stops a tired heater from destroying its own efficiency, and it is covered under our repairs and maintenance work.
Most homes want both, and it makes sense to do them in one visit, because the flue tells you how the appliance has been run and the appliance tells you why the flue looks the way it does. Ask for a clean and you get the flue. Ask for both and you get the whole system.
Does a gas heater have a flue that needs attention
Yes, and it gets forgotten more often than wood does, because there is no soot to make the point.
A flued gas heater vents its combustion products outside through a flue, and that flue has to be clear and intact for the appliance to be safe. Gas does not leave creosote, so the risk is different: it is blockage, corrosion and joins that have failed, and the consequence is combustion products staying in the house rather than a fire in the flue.
That is a carbon monoxide question, and carbon monoxide cannot be seen, tasted or smelled. It is the reason a flued gas heater needs a professional service on an interval rather than when something seems wrong, and our flue work covers gas heaters as well as wood.
How often, and when to book it
Once a year is the accepted interval. The NSW EPA tells householders to “clean the chimney, flue and baffle at the end of every winter”, and the South Australian EPA says the same thing from the other direction in its guidance on domestic heating smoke: “it is recommended the flue be cleaned once a year”. Fire and Rescue NSW does not commit to a number, but includes “ensure flues and chimneys are regularly cleaned” in its advice on heaters and open fires.
Heavy users should think in terms of the season rather than the calendar. A woodfire heater that runs every night from May to August is working far harder than one lit a dozen times a winter, and if you burn anything less than properly seasoned hardwood you should assume you are on the faster end of the scale.
On timing, there are two sensible answers. Before winter is the traditional one, and it means you go into the cold months with a clear flue and any faults already found. After winter has an argument too, because deposits sitting in a flue through a humid Coffs summer are what produce the smell in the room in February.
What is not sensible is May and June. That is when everybody rings at once, and the queue gets long precisely when you want the fire working.
Can you clean your own flue
You can do part of it, and plenty of people do. A brush run down from the top will shift loose soot, and if you are comfortable on a roof and the deposits are dry and light, you will get something out of it.
Where it stops being a maintenance job is hardened glazed creosote, which does not brush off, and anything involving the condition of the system itself. Assessing joins, a masonry liner, a cap or evidence of a previous flue fire is not a visual you can take from the roof with a torch. Neither is a gas flue, which should not be touched by anyone other than a licensed gasfitter.
The honest position is that sweeping is the easy half and inspection is the half that matters, and the inspection is what you are paying a professional for.
Getting your flue cleaned in Coffs Harbour
Chimney and flue cleaning is a rare service around here and we are one of very few offering it, which is not a boast so much as an explanation of why the diary fills the way it does once the weather turns.
Every clean includes an inspection, because taking the deposits out without looking at the condition of the system would only be doing half the job. We use flexible rotary brushes and vacuums, we work on wood and gas, and we clean flues on appliances we did not sell just as readily as the ones we did.
We also sell, install and repair the appliances at the other end of those flues, from wood fireplaces and woodfire heaters through to installation and ongoing repairs and maintenance. Family owned here since 1982, and still the same family.
If you are weighing up wood against the alternatives before you commit to a flue at all, our guide to choosing between a gas fireplace, a wood fireplace and an electric flame fire is the better place to start.
FAQs
How often should a flue be cleaned?
Once a year for most homes, ideally before the cold weather starts. If you run the fire most nights through winter, or you burn wood that is not properly seasoned, you are in the group that should not stretch it past twelve months. Light users can sometimes go longer, but that should be a decision made after an inspection rather than an assumption.
What happens if I have never had my flue cleaned at all?
It can still be cleaned, and being years overdue is not a reason to avoid making the call. Expect it to take longer than a routine clean, expect hardened deposits rather than loose soot, and expect the inspection to matter more than usual, because a flue that has never been looked at is the most likely place to find a damaged cap, a moved join or signs of a previous flue fire.
How do I know if my flue is blocked?
The two clearest signs are a fire that has become difficult to start and smoke entering the room when you open the door. Blackening glass, more wood for less heat and a smell from the fireplace on humid days all point the same way.
Does a chimney fire damage the flue permanently?
Sometimes, and that is why one needs assessing rather than just sweeping. A short, hot burn can distort flue sections, damage a liner or wreck the cap. Some systems come through fine and only need cleaning. The point is that it is not safe to assume either way without someone looking at it.
Do gas heaters need their flues cleaned?
Flued gas heaters need their flues checked and kept clear, yes. There is no creosote involved, so the concern is blockage, corrosion and failed joins, and the consequence is combustion products entering the room instead of venting outside. That makes it a carbon monoxide issue, and it is licensed work.
Will a flue clean fix a fire that will not draw?
Usually, because a restricted flue is the most common cause. It is not the only one. A flue that is too short, a heater sitting against an outside wall, a damaged liner or a baffle that has shifted will all affect the draw, and none of those are solved by sweeping.
Do you clean flues on heaters you did not sell?
Yes. We clean and service appliances bought anywhere, as long as they meet Australian Standards. Plenty of the flues we work on came with the house.
Book Your Flue Clean Before the Queue Starts
The fire you are going to light in May is connected to a flue that has been getting slowly worse since the last time you used it. It costs very little to find out what condition it is in, and a good deal more to find out the hard way.
We will clean it, inspect it, and tell you honestly whether the appliance at the bottom needs anything while we are there.
Come and see us at 92 Industrial Drive, North Boambee Valley, call (02) 6652 2411, or send us an enquiry. We look after Coffs Harbour, Scotts Head, Dorrigo, Grafton and everywhere in between.
Written by the team at Coffs Gas Company.
Disclaimer: This article is general information only. Appliance and flue requirements vary between manufacturers, models and installations, and the guidance here is current at the time of writing. Follow the manufacturer’s documentation for your specific appliance, and have solid fuel and gas appliances installed and serviced by a licensed professional. If you suspect a fire in your flue, leave the building and call 000.
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