Can you burn coal and heat logs together in a multi-fuel stove?

Homes across the UK frequently feature multi-fuel stoves rather than dedicated wood burners. These versatile appliances are equipped with a raised grate and an ash pan, theoretically allowing homeowners to burn either wood or smokeless coal.

As eco-friendly compressed heat logs become more popular, many people wonder if they can mix their remaining bags of coal with the new briquettes to create the ultimate fire. While it might seem like a logical way to combine heat sources, mixing coal and wood products in the same firebox is highly discouraged. Here is the technical explanation of why burning them together causes problems.

The main reason you should not mix the two fuels is that they require completely opposite airflow dynamics to burn efficiently.

• Smokeless coal: Coal needs a constant supply of oxygen from below. To burn coal efficiently, you must open the primary air vent at the bottom of the stove, allowing air to rush up through the raised grate.

• Heat logs and wood: Wood products burn best on a flat bed of ash and require oxygen from above. To burn wood, the primary air vent is closed, and the secondary air vent (at the top) is opened.

If you put both fuels in at the same time, you cannot optimise the airflow. Either the coal will lack oxygen and smoulder uselessly, or the heat logs will receive too much air from below and burn out in minutes.

There is a more serious, hidden danger to mixing these fuels. All coal, even modern smokeless varieties, contains trace amounts of sulphur. When coal burns, it releases sulphur dioxide into the firebox.

Even though premium heat logs have an extremely low moisture content (under 10%), burning any wood product naturally releases water vapour. When the sulphur dioxide from the coal mixes with the water vapour from the wood inside the chimney, it creates a highly corrosive chemical compound known as sulphuric acid.

Over time, this acid will eat away at the metal lining of your stove, severely corrode a stainless steel flue liner, and cause irreversible, expensive damage to the entire heating system.

To protect your appliance and get the best heat output, always burn fuels independently. If you want a quick, bright, and intense fire, clean the grate and burn solely heat logs or kiln dried wood with top airflow. If you require a fire to last all night with minimal attention, use solely smokeless coal with bottom airflow. Never mix the two in the same lighting cycle.