How Does an Oil Filled Radiator Work

Maybe you’ve had oil filled space heaters in your home throughout your life, but you don’t know how they operate, or how efficient they are when they’re heating your home.

Oil filled radiators are common throughout the UK, but most people don’t know what mysterious inner mechanisms are bringing these devices to life. While some people are happy to go their entire lives without knowing the parts and components of an oil filled heater, others like to know exactly what makes each of their products tick.

If you’ve always wondered exactly how does an oil filled radiator work, or you’re keen to see how energy efficient oil filled electric radiators are, you’re in the right place.

Here’s what you need to know about your oil filled radiators.

What Is an Oil Filled Radiator?

This modern heating solution uses an electrical element to heat a reserve of unique thermal oil within the appliance. Because the heating technology is fully emersed within the oil, when it heats up, that heat then transfers to the surrounding liquid.

The main difference between an oil filled radiator and a standard central heating solution that uses the convection process is that your central heating radiator uses the boiler and an interconnected system of pipes. Convection heaters also use hot liquid to heat a space, but they rely on an external heating technology, while your oil filled heater has the heating solution within the appliance itself.

Your oil filled electric radiator is a versatile standalone unit that you can use anywhere with an electric power outlet. Alternatively, your central heating convection unit is just an empty shell until some hot water reaches it from your boiler.

Notably, the high heat element within your oil heaters is often simpler than you’d think. An oil filled radiator typically uses a coil of metal resistive wire that’s inserted into the base of the oil heater. When you apply an electric current to these oil filled heaters by plugging them into an outlet, the electrons in the wire jostle together and create friction, which leads to heat.

The diathermic oil in your radiator gradually warms up, and since this oil fills the full radiator, the heating element eventually creates a hot product that can warm up your room. The amount of heat that comes from the surface area of your oil radiators can depend on several factors.

What Features Should I Look for in an Oil Heater?

Oil heaters can come with a lot of confusing sounding features and options. Just like choosing an air or halogen heater, it’s important to know what you should be looking for when you’re making your choice. Start by making sure you have enough width back at home in the area you want your radiator to go in. How big does your device need to be?

You might be able to find out how does an oil filled radiator work and how quickly your radiator heats up by reading the information provided by the manufacturer, so if you want a speedy solution, keep that in mind. Other features to look out for include:

man adjusting heater temperature

• An LCD screen and display panel where you can see the temperature

• Timer functions and automatic switch-off solutions

• Frost protection to ensure the heater switches on when a room reaches a certain temperature

• Safety features like automatic switch off

• Ease of use: how simple is the device to use?

• Energy efficiency ratings

How Long Does It Take for an Oil Filled Radiator to Heat Up?

If you’re wondering whether you get better heat output from a diathermic oil radiator or a standard central heating radiator, then you might wonder how long it takes for these devices to heat up. Crucially, oil radiators do take a little longer to heat up than their oil-free counterparts. However, they also cool down more slowly too, which means that a portable oil filled radiator could keep you warm for longer even after you have switch it off. The diathermic oil within the oil filled radiator has a very high boiling point and heat capacity.

Diathermic oil inside your heater can absorb a lot of energy before it begins to heat up, which means it can radiate heat for a long time without cooling down. A normal oil filled heater with a 2kW power supply could be so slow to cool down that you could save on power and leave the room feeling warm for longer than you could with a standard central heating radiator. You don’t even need to replace the oil inside the heater, as it remains in fantastic condition for a long time.


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Just like any air or convection heater, do keep in mind that your oil radiator may become less efficient over time. All technology eventually suffers from wear and tear. If you notice that the air in your room doesn’t heat up as quickly after a few years of using your oil heater, you might need to look into upgrading to a new device. A slower than usual heating time is just one sign that your oil heater might be nearing the end of its life.

Do Oil Filled Radiators Use a Lot of Electricity?

An oil heater can be a more efficient way to heat a home than you realise. Oil filled radiators and space heaters might be lighter on the pockets than using central heating. Oil heaters will usually make more sense than central heating when you’re only heating one single room. With a space heater, you can heat one room and keep it warm for a long period of time, without having to use your boiler to fill numerous radiators in the house.

According to the Centre for Sustainable Energy in the UK, the efficiency of your oil space heaters, and how much energy they use can depend on numerous factors. The size of your heater, the surface area the oil needs to fill, and the energy efficiency factors considered in designing the heater are all important components.

In general, a 2KW oil-filled radiator will come around 21 pence per hour, while a halogen heater could only come about 18 pence an hour. A fan heater can come up to 28 pence per hour to run.

Choosing the right radiators for your needs means considering your situation carefully. Halogen heaters might heat a space faster, but they’re not ideal for larger rooms. Although oil heater products take longer to heat up, their heat retention is much better than that of a halogen space heater.

The radiators oil in your oil space heater will stay warm for longer, and it can heat up a room of virtually any size. Both options are far more efficient than using an air heater, as air heaters and heated fans can struggle to maintain a consistent temperature.


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Why Are Oil Heaters So Efficient?

Oil filled heaters are known to be extremely efficient, thanks to their unique heat reservoir. You don’t have to fill up columns of water like you do with central heating. The columns in your oil radiator are already filled with unique warm oil. This gives you an advantage when it comes to lowering your energy bill. You can even search for features in an oil heater that match your needs, such as unique shapes of radiator fins, or heater fins, and a control panel for easy use.

Almost all of the electricity consumed by your oil electric radiators is transformed into heat. Very little energy goes into running any extra features, which is one of the reasons why these products are so efficient. You can even control the way the heating element works in your oil filled radiator with thermostat tools and timers.

Just make sure that you research the energy efficient heater you’re interested in before investing. Looking at things like bottle capacity, and high specific heat capacity could help you to make a more informed decision.

Are Oil Heaters Safe to Leave on Overnight?

Energy efficiency isn’t the only benefit of using oil filled heaters. These oil radiators and space heaters are also excellent for peace of mind. Most manufacturers of oil filled radiators agree that they’re safe to leave on throughout the night if you need to. However, most of the time, you won’t have to leave your oil filled heaters on all night anyway.

couple in winter outfit

Oil heaters will come with safety features inside the heater to protect against the risk of fire and overheating. Making sure that these safety features are in place will give you peace of mind. However, because the boiling point of the oil inside of your heater is so high, you should be able to get full room coverage and warm the air in your living rooms quickly, then turn the heater off again.

One of the biggest benefits of the oil filled heater is how it can hold onto heat and keep warming your home and the air around you, even when it’s switched off. You don’t have to keep the heater turned on after your room reaches the right temperature to avoid the air cooling down too quickly. The surface temperature of the heater will stay high, so the room temperature will too.

An oil heater shouldn’t be more dangerous to leave on overnight than a convection heater. You might find these products are even safer than some air heaters. However, if you’re uncomfortable, you can turn the heater off when your room reaches the right temperature, and rest well in the knowledge that your space should stay warm for some time. Other tips to keep yourself safe include:

• Never leave any heating solution unattended for too long

• Avoid leaving heaters on while you sleep if you can

• Position your heater away from objects that might knock them over

• Keep heaters at least a decent distance away from combustible fabrics

• Don’t buy second-hand heaters

• Avoid using extension leads

• Regularly inspect your heater for damage

Finishing Up

So if you’re still wondering how does an oil filled radiator work, we haven’t done a very good job, have we? There is lots of information about your oil filled radiator in the included information booklet.

Alternatively, if you have any questions, or perhaps you have some handy tips and tricks or fun facts about radiators, leave us a message in the comments.


  1. Thank you so much for the informative article. By chance, have you done any research, where you can recommend reliable brands and models that are not manufactured from China and that can also be purchased in the U.S.?

  2. Jim an Pam says:

    Thank you for the info, we live full time in a RV we have one and we love it

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