If you’ve ever run your stove on a slow burn—maybe overnight or just to keep it ticking over gently—you might not realise it could be doing serious harm to your flue liner. It’s a common practice that many stove users rely on, but it can lead to unexpected and costly problems.
Let’s dive into why slow burning can damage your flue liner, what makes this happen, and what you can do to keep your stove running safely and efficiently.
Estimated reading time: 6 minutes
Table of contents
What Is Slow Burning?
Slow burning, often referred to as slumbering, is when a stove is operated at low temperatures or shut off, either to keep it going for long periods (like overnight) or simply to save fuel. It’s especially common when stoves are linked to a boiler or used in homes where steady, low heat is preferred.
While it might feel like a smart, economical way to use your stove, slow burning often means the fire doesn’t get hot enough to fully burn the fuel or properly vent exhaust gases. This is one of the worst things to do for your flue liner.
How Does Slow Burning Cause Damage?
1. Condensation Build-Up
When a stove runs cool, the flue system doesn’t get warm enough to carry away all the combustion gases. These gases cool down too quickly and turn into condensation inside the flue liner.
If you’re burning wood or coal derivatives, that condensation mixes with chemicals from the fuel—like sulphur and chlorine—to create acidic compounds. Over time, this can eat away at the metal liner, leading to serious corrosion.
2. Corrosion from Acid
The acids formed by condensation, especially sulphuric and hydrochloric acid, are incredibly corrosive. Flue liners made from 316-grade stainless steel (a common material) are particularly vulnerable. These liners, which were originally sold with a 10-year guarantee, often didn’t last that long when used in stoves that were regularly slow-burned.
Photo Source: Bonds Chimney Sweep
In response to this problem, manufacturers developed 904-grade stainless steel liners. These are much tougher and come with a 25-year guarantee, but even they aren’t immune to damage if the stove is frequently run at low temperatures.
3. The Role of Fuels
While burning wood is often linked to condensation issues in flue systems, research shows that coal derivatives, including smokeless fuels, can cause similar damage. When burned inefficiently, such as during a slow burn, these fuels can produce excess moisture and acid, significantly increasing the risk of condensation buildup and corrosion within the flue liner.
Wood under 20% moisture content should only be used and smokeless fuels like anthracite, smokeless coal, and manufactured briquettes are cleaner burning, emitting less smoke and soot.
However, if used improperly, they can still lead to blockages and damage over time. Burning them at the correct rate helps ensure flue liners stay clear, extend their lifespan, and maintain efficiency while reducing harmful emissions.
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The Risks of Ignoring the Problem
Slow burning might feel harmless in the short term, but the long-term consequences can be significant. Here’s what you’re risking:
- Costly Repairs or Replacement: Corroded flue liners might need replacing much sooner than expected, which can be an expensive job.
- Reduced Stove Efficiency: A damaged liner affects how well your stove vents gases, making it less effective at heating your home.
- Health Hazards: Corroded liners can allow dangerous gases like carbon monoxide to leak into your home.
- Increased Fire Risk: Acidic deposits and creosote build-up from slow burning raise the chances of a chimney fire.
How to Prevent Flue Liner Damage
To prevent damage, reduce the fire gradually, allowing proper airflow without completely suffocating it. Ensure the fire is completely extinguished before leaving the stove overnight, and always begin with a clean, fresh burn the following day.
It’s also essential to have your chimney professionally swept at least once a year to maintain safe and efficient operation.
If you want to keep your flue liner in good condition and avoid costly problems, here are some practical steps you can take:
1. Avoid Prolonged Slow Burning
This is the simplest and most effective solution. Try to run your stove at a proper temperature—hot enough to fully burn the fuel and vent gases efficiently. A stove thermometer can help you monitor this.
2. Burn the Right Fuel
Use dry, seasoned wood if you’re burning logs. Wet or green wood produces more condensation, so it’s best avoided. If you’re burning coal derivatives, choose high-quality, stove-approved smokeless fuels.
3. Upgrade to a 904-Grade Liner
If your current flue liner is the older 316-grade, consider upgrading to the more durable 904-grade. It’s better equipped to handle the acidic by-products of combustion, especially in stoves that are occasionally run cooler.
4. Insulate Your Chimney
An insulated chimney keeps the flue liner warmer, helping to prevent condensation from forming. This is particularly important if your chimney is on an external wall or exposed to cold weather.
5. Keep Up with Maintenance
Annual chimney inspections and regular sweeping are a must. A professional sweep can spot early signs of damage, remove creosote build-up, and keep your flue system in good working order.
The Bottom Line
While slow burning your stove might seem like a good way to stretch your fuel or keep the fire going overnight, it can cause serious damage to your flue liner. From condensation and acid formation to costly repairs and safety risks, the downsides of slow burning far outweigh the benefits.
By burning your stove at the right temperature, using quality fuels, and keeping up with maintenance, you can protect your flue liner and enjoy your stove worry-free. Investing in a durable liner and proper chimney insulation will also save you money and stress in the long run. Keep your stove burning brightly—and safely!
FAQ
Slow burning creates cooler flue temperatures, which lead to condensation inside the liner. This condensation mixes with combustion by-products to form acids, which corrode the liner over time.
A Strange or acidic smell will be coming from the stove or chimney. There also may be a reduced performance of your stove and visible rust or flaking inside the flue.
Yes, but you need to do it properly. Avoid letting the fire smoulder. Use dry, seasoned wood or a good-quality smokeless fuel, and ensure the stove is burning at a steady, moderate temperature.
At least once a year, though twice is recommended if you use your stove regularly. Frequent cleaning helps remove acidic deposits and reduces the risk of damage or fires.
If your current liner is 316-grade, upgrading to a 904-grade liner can be a smart investment. It’s more resistant to corrosion, especially if you occasionally slow-burn your stove.
