Log Sizes & Burn Performance: The Complete Guide
When it comes to firewood, size really does matter. From quick-lighting small logs to long-lasting large logs, the dimensions of your firewood directly affect how efficiently it burns, how much heat it gives off, and how often you need to refuel your stove or fireplace.
In this guide, we’ll break down the most common log sizes, explain how they impact burn performance, and share expert tips on choosing the right log size for your stove, fireplace or outdoor fire pit.
Why Log Size Matters
The size of a log affects:
- Burn speed: Small logs catch fire faster but burn down more quickly. Large logs burn slower and release heat over a longer period.
- Heat output: Bigger, denser logs tend to produce a steadier, more consistent heat.
- Ease of use: Smaller logs are ideal for kindling or quick top-ups, while larger logs reduce how often you need to refuel.
- Compatibility: Log size must fit your appliance. Many stoves have a recommended maximum log length.
Log Size Comparison Table
| Log Type | Typical Length | Burn Speed | Heat Output | Best For | Key Benefits |
|---|---|---|---|---|---|
| Small Logs | 20–25 cm | Fast | Moderate | Small stoves, quick top-ups | Easy ignition, ideal for starting fires or short burns |
| Medium Logs | 25–30 cm | Moderate | High | Most standard stoves | Balanced burn speed and heat output |
| Large Logs | 30–40 cm | Slow | High | Large stoves, open fires | Fewer refuels, steady heat, longer-lasting flames |
| Slow-Burning Logs | 30+ cm | Very Slow | Very High | Overnight burning | Perfect for long burning logs, maximum efficiency |
Small Logs: Quick Heat & Easy Lighting
Small logs are cut thinner and shorter, making them ideal for:
- Quick ignition: Their smaller surface area means they catch fire easily.
- Top-up burning: Perfect for boosting heat output without overloading your appliance.
- Small stoves and fireplaces: They fit easily and burn efficiently in compact spaces.
Typical Use Cases:
- Starting a fire quickly.
- Providing short bursts of heat during milder weather.
- Mixing with large logs to control temperature and burn speed.
Large Logs: Long-Burning Heat
Large logs are the go-to choice for those who want sustained heat output. Their size means they take longer to ignite but reward you with:
- Extended burn times: Bigger logs smoulder for longer, making them perfect for slow burn logs.
- High, steady heat: Ideal for long winter evenings or overnight burning.
- Less ash production: Larger logs tend to burn more completely, creating less ash to clean up.
Typical Use Cases:
- Overnight burns in wood-burning stoves.
- Open fireplaces where visual impact matters.
- Mixing with smaller logs to maintain a steady fire.
What Makes Long Burning Logs?
A long-burning log isn’t just about size. Several key factors contribute to burn performance:
- Wood Density – Dense hardwoods like oak or birch burn slower and produce more heat than softwoods.
- Moisture Content – Kiln-dried logs with moisture content below 20% burn hotter and longer because less energy is wasted evaporating water.
- Log Size – Larger logs smoulder slowly, making them excellent slow burning logs, while smaller logs burn faster due to their increased surface area.
- Airflow – The way logs are stacked in your stove or fireplace affects how they burn. Tighter packing can slow combustion, while good airflow speeds it up.
- Stove Efficiency – Modern stoves with secondary burn technology extract more heat from each log, making even mid-sized logs burn for longer.
Mixing Log Sizes for the Best Results
In practice, the best fires are created with a mix of small logs and large logs:
- Start small: Use small logs or kindling to get the fire established.
- Add medium logs: Once a good ember bed is formed, add medium logs to build steady heat.
- Finish with large logs: When the fire is hot, add larger slow burn logs for a slow, controlled burn.
This method not only improves efficiency but also helps you make the most of your firewood supply.
Choosing the Right Size for Your Appliance
Different heating appliances have different log size requirements:
- Small Stoves (3–5 kW): Best with small logs (20–25 cm).
- Medium Stoves (5–8 kW): Use medium logs (25–30 cm) for steady, balanced heat.
- Large Stoves/Open Fires (8+ kW): Can handle large logs for long burning logs overnight.
If you’re unsure, choose medium-sized logs — they’re versatile and work in most stoves and fireplaces.
Key Takeaways
- Small logs = fast lighting, quick heat.
- Large logs = slow, steady, long burning logs.
- Moisture content, density, and stove efficiency also affect burn performance.
- Mixing log sizes gives you the best of both worlds.
By understanding log sizes and how they impact burn performance, you can optimise your fire for efficiency, convenience and comfort.