Homeowners Professionals

How does an oil fired boiler work?

Oil boilers are less common than gas boilers, however there are over four million homes in the UK that aren’t connected to the gas main. This means that these four million homes need to be heated in other ways. An oil boiler is often the best way to do this. The oil tank can be fitted on site and filled with oil as and when it’s needed.

How does an oil boiler work?

An oil boiler works in a very similar way to a gas boiler. The fuel, in this case oil, is ignited in the combustion chamber and a heat exchanger warms up cold water, either from the mains in a combi system or from a cold water tank in a conventional system. The heated water can be used in your radiators, taps and showers to provide your home with heating and hot water.

An oil boiler should reach the same efficiency as a gas boiler. According to building regulations, oil boilers must have an energy rating of at least 86 per cent, or A+. A condensing oil fired boiler will usually have an efficiency of 90 per cent or higher. Oil is a more efficient fuel than gas. This is because oil boilers use nearly all of the heat and additional gas that’s created from the burning of fuel, turning this into extra heating energy so there’s less wastage. This means you’ll get a good return on every unit of energy.

The main difference between a gas and an oil boiler is the way the appliances store their fuel. A gas boiler doesn’t need to store gas because it is connected to the mains, which means it has a constant supply of fuel. In contrast, an oil boiler requires a tank to store the oil until it is needed.

The oil tank should be located on your property and there are certain installation regulations that need to be followed. The base of the tank must be strong enough to support the weight of the tank and its contents. The tank must sit on solid ground, either concrete or paving slabs that are at least 42mm thick and that extend out at least 300mm beyond the perimeter of the tank. If the tank is located quite close to your house, a fire wall must be positioned between the tank and your home. 


Modern oil tanks are usually made of plastic and are relatively easy to maintain. The tank will need to be refueled as necessary to ensure that you don’t run out of oil at any point. Some people will only need the tank to be refilled once a year, however for larger homes with more radiators, you may find that the tank has to be refilled a couple of times each winter.

Just like in a gas heating system, your home should have at least one thermostat that tells you the room temperature, weather compensation or smart controls. A thermostat should be placed away from a radiator and out of direct sunlight so it is providing an accurate

How environmentally friendly are oil boilers?

It’s generally considered that oil boilers aren’t as environmentally friendly as their gas or electric counterparts. However, regardless of the fuel your boiler uses, home heating accounts for a large proportion of total carbon production in the UK. This means that if you’re heating your home using gas, oil or electricity, you’re not going about it in the most environmentally friendly way. When compared to gas boilers, however, it’s thought that oil boilers could be slightly more efficient and produce a bit more heat while using less fuel. But as with any boiler, it can become much less efficient over time if it isn’t looked after and serviced regularly.

If you really want to create a greener home and reduce the size of your carbon footprint, you may consider using something like a heat pump instead. When used in tandem with solar panels, the impact on the environment is much smaller and far more eco friendly.

How much oil does my boiler use per hour?

The average home in the UK that uses an oil boiler to heat the property is thought to use around 17,000 kWh on heating. Most oil boiler systems use kerosene and one litre of kerosene equals around 10 kWh. This means that in one year, you would use approximately 1,700 litres of oil to heat your home and to provide hot water. But how can we use this to work out how much oil your boiler uses per hour?

Firstly, you don’t have your heating on every single day. Therefore, of this 1,700 litres of oil, most will be used in autumn and winter and much less in spring and summer. As an example, we’ll say that you have the heating on for six months of the year (or 180 days). Therefore, we must divide 17,000 kWh (the total energy usage in one year) by 180 days to give us the approximate amount of kWh used per day in six months. This equals 94.4 kWh.

Now that we have the amount of energy being used per day while your heating is on, we need to calculate how much oil is actually being used. Therefore we will take our 94.4 kWh and divide this by the amount of kWh in one litre of kerosene (10 kWh) to give us 9.4 litres. This is how much oil you would use per day if your boiler was heating your home for 24 hours a day for six months. However, it’s much more likely that you’ll heat your home for just a few hours.

So, finally, we can take 9.4 litres and use the number of hours your heating is on to get our final answer. We’ll say that this is six hours a day. In a 24-hour period, there are four lots of six hours, and so the calculation would be 9.4 litres divided by four. This gives us a total of 2.36 litres. Therefore, your oil boiler uses approximately 2.36 litres of oil a day if your heating were to be on for six hours, or 0.39 litres per hour.

Will oil boilers be banned?

The government has mentioned that gas boilers will be banned from being installed in new build homes from 2025. This also applies to oil boilers too. While this doesn’t mean that you have to switch out your oil boiler that’s in perfect working order in your current home, it could make you think twice about getting a replacement when it’s needed. The UK are planning to be completely emission-free by 2050, so it’s absolutely worth considering alternative ways to heat your home now. 

How to clean an oil fired boiler

Just like any other heating system, an oil boiler will need cleaning to ensure there isn’t any dust, soot or debris present that could be reducing its efficiency.

If you want your boiler to have a thorough clean, you should get a suitably qualified engineer to do this for you. They will be able to check the condensate drain and clean both the siphon and combustion chamber/heat exchanger surfaces if your oil boiler is a condensing type.

You shouldn’t try to remove the boiler casing yourself in order to clean it. This should only be done by a competent or OFTEC registered engineer, otherwise your warranty may be void.

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