How to cofire: Mixing fuels for maximum efficiency

While traditional house coal is no longer available for domestic use in the UK, the principle of cofiring – mixing different fuel types in your stove or fireplace – remains one of the most effective ways to maximise heat output and efficiency. By combining traditional logs with modern heat logs, wood briquettes, or smokeless coal, you can achieve longer burn times, more consistent warmth, and better value from your fuel supply.

Here we explain how you can cofire to get the most from your fuel, and show you which fuel combinations deliver the best results for your home.

What is cofiring?

Cofiring is the practice of burning two or more different fuel types together in the same fire. Rather than relying on a single fuel source, cofiring takes advantage of the different properties of various fuels – their burn rates, heat output, and how they burn – to create a more efficient, longer-lasting fire.

Cofiring used to mean burning coal and wood together, but household coal was banned for domestic use in the UK in May 2023, so modern cofiring focuses on combining kiln-dried firewood with manufactured fuels like heat logs or briquettes.

The concept is straightforward: some fuels burn hot and fast, providing immediate intense heat, while others burn slowly and steadily, offering sustained warmth over several hours. By combining these complementary fuel types, you get the best of both worlds: quick heat when you need it and extended burning time that keeps your home warm without constant attention.

Why does cofiring work?

Different solid fuels have distinct burning characteristics that make them suited to different purposes:

• Traditional firewood ignites relatively easily, creates attractive flames, and provides good initial heat. However, wood burns through fairly quickly, requiring regular refuelling to maintain warmth
• Heat logs and wood briquettes are made from compressed wood materials with very low moisture content. They’re incredibly dense, burn much hotter than regular logs, and last significantly longer – often two to three hours per heat log
• Smokeless coal produces intense, long-lasting heat with minimal smoke and ash. It burns slowly and steadily but can require a well-established fire to ignite properly

When you combine these fuels strategically, each compensates for the other’s limitations. Fast-burning fuels help ignite slower-burning ones, while long-burning fuels extend your fire’s life and reduce the need for constant refuelling.

The benefits of cofiring

• Extended burn time: By combining fast and slow-burning fuels, you can maintain warmth for several hours without constantly adding fuel. This is particularly valuable during evenings or overnight
• Improved efficiency: Cofiring optimises combustion by maintaining consistent temperatures and better airflow. This means you extract more heat from your fuel and waste less energy
• Cost savings: While heat logs and smokeless coal tend to cost more per kilogram than traditional firewood, they produce significantly more heat and last much longer. Cofiring allows you to use premium fuels alongside cheaper options, balancing performance with cost
• Reduced maintenance: High-quality heat logs and smokeless coal produce far less ash than traditional logs. And less ash means less frequent cleaning and easier maintenance of your stove or fireplace
• Flexibility: Cofiring gives you options. Running low on one fuel type? You can adjust your ratio or switch combinations based on what you have available while still keeping warm
• Better heat consistency: Rather than the fluctuating temperatures you get with fast-burning logs alone, cofiring provides more stable, sustained warmth that keeps your home comfortable without dramatic temperature swings

Best fuel combinations for cofiring

Traditional firewood with heat logs: This is perhaps the most popular and practical cofiring combination for modern households. Products like Hotties XL and Roastie Toasties work brilliantly alongside regular firewood

How it works: Start your fire with kindling and traditional logs to establish a good flame and heat base. Once the fire is burning well, add one or two heat logs. The traditional logs provide the initial flames needed to ignite the denser heat logs, while the heat logs then take over, providing intense, sustained heat for hours.

Benefits:

• Extended burn time without constant refuelling
• Higher overall heat output than logs alone
• Reduced ash production compared to burning only traditional wood
• Cost-effective, as heat logs last much longer than equivalent weight in traditional logs
• Convenient: pre-formed heat logs are consistent in size and easy to handle

Best for: Wood-burning stoves, multi-fuel stoves, and open fireplaces. Ideal for evening heating when you want consistent warmth without repeatedly adding fuel.

Smokeless coal with traditional firewood

For multi-fuel stoves in Smoke Control Areas, combining smokeless coal with wood offers powerful, long-lasting heat.

How it works: Establish a strong wood fire first using kindling and logs. Once you have a good bed of hot embers, add smokeless coal. The established heat from the wood fire will ignite the coal, which then provides intense, sustained warmth. You can continue adding small amounts of wood for flame and ambience while the coal provides the heat foundation.

Benefits:

• Exceptional heat output: smokeless coal produces significantly more heat than wood alone
• Very long burn time – coal can smoulder overnight
• Approved for Smoke Control Areas when using authorised smokeless fuel
• Economical for extended heating periods
• The wood provides attractive flames while coal provides sustained heat

Best for: Multi-fuel stoves, particularly if you want overnight burning capability or extended daytime heating with minimal refuelling.

Kiln-dried logs with wood briquettes or heat logs

Another excellent combination uses premium kiln-dried hardwood logs alongside compressed wood briquettes or heat logs.

How it works: Kiln-dried logs have very low moisture content (typically under 20%), making them efficient burners that produce good heat and minimal smoke. When combined with even denser compressed briquettes, you create a long-lasting fire that burns efficiently.

Benefits:

• Both fuels are Ready to Burn certified and compliant with all UK regulations
• Minimal smoke and emissions – important for Smoke Control Areas
• Very low ash production makes cleaning easier
• Excellent heat output from both fuel types
• Suitable for all stove and fireplace types

Best for: Those prioritising clean burning and efficiency, particularly in Smoke Control Areas or for anyone with respiratory conditions.

How to cofire effectively: Top tips

Getting the best results from cofiring requires understanding the proper technique:

1. Start with the right base. Always begin with kindling and the faster-burning fuel (traditional logs or firelighters) to establish a strong fire. Never try to light dense heat logs or smokeless coal from cold – they need existing heat to ignite properly.
2. Layer strategically. Add your slower-burning, denser fuels (heat logs, briquettes, or smokeless coal) once your initial fire is well established with good flames and a bed of hot embers. This ensures they ignite properly and burn efficiently.
3. Don’t overload your fire or stove. Resist the temptation to pack your stove or fireplace full. Overcrowding restricts airflow, which is essential for efficient combustion. Leave space between fuel pieces for air to circulate.
4. Control airflow. If you’re using a wood-burning stove, adjust the air vents to suit the fuel combination you’re using. Dense fuels like heat logs and smokeless coal need good airflow to burn efficiently, while too much air will cause traditional logs to burn through too quickly.
5. Time your fuel additions. Add your longer-burning fuels (heat logs or coal) when you still have good heat and flames, not when the fire is dying down. This ensures they’ll catch light properly and will burn efficiently.
6. Consider proportions. A good starting ratio is roughly 60-70% longer-burning fuel (heat logs or coal) to 30-40% traditional logs – but of course, you can adjust based on your preferences for flame appearance versus long-lasting heat.

Choosing the right fuels to cofire

If you’re new to cofiring, keep it simple to start with. Combine traditional firewood with one type of heat log to get familiar with how they work together. Pay attention to how long different combinations burn, how much heat they produce, and how often you need to refuel.

As you gain experience, you’ll develop an instinct for the right fuel ratios and timing for your particular stove or fireplace. Every appliance behaves slightly differently, so some experimentation will help you find the perfect combination for your needs.

And of course, when selecting fuels for cofiring, prioritise quality:

• Look for Ready to Burn certification on wood products, ensuring moisture content below 20%
• Choose approved smokeless fuels if you live in a Smoke Control Area
• Select reputable heat logs like Hotties XL or Roastie Toasties that are designed for cofiring
• Store all fuels properly in dry conditions to maintain their performance

We stock a comprehensive range of cofiring fuels including traditional firewood, Hotties XL heat logs, Roastie Toasties, and a range of smokeless coals. With the right combinations and techniques, you’ll get more heat, longer burn times, and better value from every fire you light.