If your plant runs a boiler, furnace or thermic fluid heater on liquid fuel, the choice usually comes down to two options: Light Diesel Oil (LDO) or Furnace Oil (FO). Both are well-proven industrial fuels, but they behave very differently in storage, in the burner and on your monthly fuel bill. Picking the wrong one can mean clogged burners, extra maintenance or paying more for heat than you need to.
This guide explains the practical differences so you can choose with confidence.
What is Light Diesel Oil?
LDO is a light, free-flowing distillate fuel. Because it has a low viscosity, it can be pumped and burned in most conditions without any preheating. That makes it simple to store and handle, and it suits small and medium boilers, furnaces, and slow- or medium-speed diesel engines.
What is Furnace Oil?
Furnace Oil is a heavier, residual fuel. It is thick at room temperature, so it has to be heated both in storage and again before the burner, to bring it to the right viscosity for pumping and atomisation. In return it is generally one of the most economical liquid fuels per unit of heat, which is why it is widely used in large boilers, furnaces and kilns that burn fuel continuously.
The key differences at a glance
- Handling: LDO flows easily and needs no heating. Furnace Oil needs heated storage and a preheater before the burner.
- Equipment: LDO works with simpler pressure-jet burners. Furnace Oil needs burners designed for heavy oil, plus heating arrangements such as steam tracing or electric heaters.
- Cost: Furnace Oil usually costs less for the same amount of heat. LDO costs more per litre but saves on heating equipment, energy and upkeep.
- Cleanliness: LDO generally burns cleaner, with less soot and fewer deposits. Furnace Oil typically needs more frequent burner and tube cleaning.
- Sulphur: Heavier fuels usually carry more sulphur. If your plant has strict emission limits, check the sulphur content of any fuel against your consent conditions.
When LDO makes more sense
- Your boiler or furnace is small or medium-sized, or runs only a few hours a day.
- You don't have tank heating or a fuel preheater, and don't want to install them.
- You want quick start-ups and minimal burner maintenance.
- You also run diesel engines or generator sets and want to stock a single fuel.
When Furnace Oil makes more sense
- You run a large boiler or furnace continuously, so fuel is your biggest operating cost.
- Your plant already has heated storage and heavy-oil burners.
- Your maintenance team is set up for regular burner and tube cleaning.
Plants that need a heavy fuel with lower sulphur often look at LSHS (Low Sulphur Heavy Stock) as a middle path.
Look at total running cost, not just the price per litre
The cheapest fuel on paper is not always the cheapest to run. When you compare, add up:
- The fuel cost for the heat your process actually needs.
- The energy used to keep heavy oil hot in storage and before the burner.
- Maintenance: burner cleaning, soot removal and downtime.
- Any upgrades needed to switch, such as a new burner or tank heating.
For a plant with high, steady consumption, Furnace Oil often wins. For smaller or intermittent loads, the simplicity of LDO usually pays for itself.
Buying tips for either fuel
- Ask for a test certificate with every batch, showing viscosity, flash point, sulphur and water content.
- Choose a supplier who can deliver consistent quality and on-time supply. A fuel that varies from load to load upsets burner settings.
- Match the fuel to your burner manufacturer's recommendations before switching.
Talk to Arabo Impex
Arabo Impex supplies Light Diesel Oil, Furnace Oil and LSHS for industrial boilers, furnaces and heaters. Share your equipment type and approximate monthly consumption, and our team will help you choose the right fuel and send a quotation.
