What Is 28-Second Heating Oil? Kerosene Explained

The short answer

If you heat your home with oil in Ireland, the fuel in your tank is almost certainly kerosene, also called 28-second heating oil. They are the same thing. When you ring a supplier and ask for "home heating oil", that is what you'll get.

So if you've been staring at an invoice or a delivery quote wondering whether 28-second oil, kerosene and home heating oil are different products, relax. For the vast majority of Irish households, it's one fuel under three names.

What is kerosene, really?

Kerosene is a light, clean-burning fuel oil refined from crude oil. It's the standard fuel for domestic boilers and oil-fired cookers (like an oil Aga or Stanley) across Ireland.

It's prized for home use because it:

• Burns cleanly and efficiently in modern condensing boilers
• Flows easily even in cold Irish weather
• Produces less soot and residue than heavier oils
• Is widely available from every oil supplier in the country

When people say "kerosene", "kero", "home heating oil" or "28-second oil", they almost always mean this same domestic-grade fuel.

Why "28-second"? Where the name comes from

The "28-second" part refers to viscosity, basically how thick the oil is and how easily it flows. It comes from an old test where oil is timed flowing through a standard measuring cup. Kerosene takes around 28 seconds, so it picked up the nickname.

The key thing to know is that the number describes how runny the fuel is, not its quality or grade in a way you need to worry about. It's just a handy label.

What about 35-second oil?

You may also hear about 35-second oil, which is gas oil (sometimes called green diesel or agricultural diesel). It's thicker than kerosene and is generally used for:

• Older or commercial boilers designed for it
• Farm machinery and some heating systems
• Larger heating setups

Most modern domestic boilers in Ireland are set up for 28-second kerosene. Putting the wrong oil in can affect how your boiler runs. If you're genuinely unsure which your system needs, check your boiler manual or ask an OFTEC-registered technician rather than guessing.

How to be sure you're ordering the right fuel

This is where a lot of buying anxiety comes from, especially if you've just moved into an oil-heated house and have never ordered before. Here's how to stay on the safe side:

1. Check the boiler plate or manual. It will state the fuel type. Almost all domestic units say kerosene / 28-second.
2. Ask the supplier plainly. Just say "I need home heating oil for a domestic boiler." That's kerosene by default.
3. If you have an oil cooker (Aga, Stanley, Rayburn), it also runs on kerosene, so a single order covers both.

If your home has an older or unusual setup and you suspect it uses gas oil, don't take a chance. A quick word with an OFTEC-registered technician will settle it for good.

A few practical things worth knowing

• Kerosene doesn't "go off" quickly, but very old oil sitting in a half-empty tank for years can pick up water and sludge. Keeping the tank reasonably topped up over winter helps.
• Cold weather isn't usually a problem for kerosene in Ireland the way it can be for thicker oils, which is another reason it's the home-heating standard here.
• The price you pay is per litre, but what actually matters to your pocket is the cost per fill. A 500 litre top-up and a 900 litre fill are very different bills even at the same unit price.

Stop guessing, and don't get caught short

Knowing your fuel is one thing. Knowing when you'll run dry, and not paying over the odds, is the part that saves real money and real hassle. A run-out is miserable: cold radiators, no hot water, and often a boiler lockout that needs restarting properly afterwards.

A few simple habits go a long way:

• Get a sense of when your tank will hit empty before it surprises you. You can see when you'll run out instead of squinting at the gauge.
• Buy on a good day rather than a panic day. Set a price-drop alert so you order when prices dip, not when you're desperate.
• Always check what suppliers near you are charging. Compare local prices by county before you commit to a fill.

Next step

Now that you know your boiler almost certainly runs on 28-second kerosene, the smart move is to never order in a panic again. Check your likely run-out date, watch for a price dip, and order your next fill on your terms.