Are Oil Filled Heaters Efficient?

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Space heaters are a great way to save money on central heating costs. These portable options only heat the spaces of your home being used, which is far more efficient. But how much it costs to run a space heater differs greatly depending on the type.

This has many homeowners wondering if oil filled heaters are efficient options.

Yes, oil filled heaters are highly efficient at heating smaller spaces. And they do so using less electricity than the average electric space heater. But this energy savings is not because these units use less electricity while running.

Confused? Don’t worry, we’ll sort it out for you. Below, we’ll look at how much energy oil filled heaters use, how this compares to other electric space heater types, and how these units save you money even though they draw the same amount of energy when they’re running.

warming hands on an oil filled heater

How Much Energy Does an Oil Filled Heater Use?

The average oil filled space heater is rated at 1,500 watts. This means that, when running on high, the unit draws about 1,500 watts of energy. Most units also have a low setting, which usually pulls about 700 watts.

To understand how much electricity an oil filled heater uses, on average, we need to convert watts to kWh. We can do this using this simple equation:

kWh = (1500 watts/hours of use) / 1,000

For every one hour a 1,500-watt oil heater is running on high, it consumes 1.5 kWh. This is a significant amount of energy. In fact, it is more than the average fridge (0.75 kWh), washing machine (1kWh), or furnace fan (1.2kWh) uses in the same amount of time.

But when you compare oil filled heaters to other types of electric heaters, you begin to see why they are widely considered to be the more energy-efficient option.

Oil vs Electric: Which Uses More Energy?

The average oil filled heater and the average electric space heater are rated at 1,500 watts. This means that they consume the same amount of energy per hour when run on high. But there are a couple of key differences that make oil heaters less expensive to run overall.


First, oil heaters are more efficient in terms of how much electricity they turn directly into heat.

The average oil-filled heater converts 99% of electricity into heat. The other 1% (or less) goes to powering the thermostat, timer, and other minor functions.

The average electric heater converts only about 98% of electricity to heat. The rest is used to power functional components and the fan.

This difference is minor, but it isn’t the only one that should be considered. How much energy these units use in the long term also plays a role in their energy efficiency.

Overall Energy Use

Electric space heaters work by heating elements inside the unit and pushing air over them to move hot air into the room. Once the unit is turned off, that heat quickly dissipates and the room cools down.

An oil filled heater, on the other hand, works through thermal mass and convection. Electricity is used to heat a resistor which, in turn, heats diathermic oil. This oil has a high thermal mass, meaning it can absorb a lot of heat and release it slowly over time.

Read More: You can learn more about how oil filled heaters work and find the best models on the market, here.

The slow release of stored heat inside an oil-filled heater means that the electric resistor needs to run less frequently. So, while both heater types use the same amount of energy when running, the oil filled heater needs to run far less often to keep the space warm.

For this reason, oil filled heaters are considered far more efficient space heating options than electric space heaters.

How Much Does it Cost to Run an Oil Filled Space Heater?

oil filled heater next to a piggy bank

Because oil filled heaters do not run at maximum power most of the time they’re in use, it can be tricky to calculate exactly how much they cost to run.

Typically, to find out how much a space heater costs in terms of energy use, you would use an energy cost calculator. But in the case of an oil filled heater, this will only tell you the cost if the heater were to run on high the entire time it was in use, which is very unlikely.

On average, the typical oil filled heater used in a size-appropriate space for at least 4 hours at a time, will only use full power about half the time it is on. The other half of the time, almost no power will be drawn because the resistor won’t be on.

Note: Compared to the typical electric space heater, the average oil filled heater will cost about half as much to operate.

Heater TypeCost per Day (8 hour runtime)Cost per day (24 hour runtime)Cost per month (at 8 hr/day)Cost per month (at 24 hr/day)
Oil Filled (on high – 1500 watts)$0.80$2.40$25.00$74.40
Oil Filled (on low – 700 watts)$0.37$1.12$11.47$34.72
Electric (on high – 1500 watts)$1.24$4.32$43.20$129.60
Electric (on low – 700 watts)$0.67$2.02$20.16$60.48
The above calculation utilizes an average electricity cost of 12 cents per kWh. But be aware, the cost of electricity varies by location.

As you can see, oil-filled heaters cost a lot less to operate than traditional electric heaters. In fact, they are one of the cheapest space heaters to run.

But do keep in mind that these costs are based on optimal conditions. When used in a size-appropriate space (closed rooms of about 170 sq ft) and run for extended periods (at least 4 hours to allow for warm-up time), oil filled heaters use about half as much electricity as traditional electric heaters.

For larger spaces or shorter runtimes, there are cheaper heating options out there.

Benefits and Drawbacks of Oil Filled Space Heaters

One clear benefit of oil filled heaters is that they are very energy-efficient. But the reasons to choose an oil filled heater go far beyond this.

Some of the most important benefits of an oil-filled heater are:

  • They heat spaces more effectively. Because they rely on slow-release thermal mass and convection, they are able to provide lasting warmth with less energy use.
  • More accurate thermostats. Because of how they operate, the thermostats on these units tend to be far more accurate than those on electric, fan-based space heaters.
  • Last longer. Oil filled space heaters have fewer moving parts than electric units and thus, tend to last much longer.
  • Safer. There are no exposed heating elements on oil filled heaters and the surface never gets too hot to touch, meaning they are safer to use around children and pets.
  • Don’t dry the air. Because they work without fans, oil filled heaters don’t dry out the air.
  • Very quiet. Even when powered up, these units put off very little noise.
  • Unlikely to tip over. The larger size and wide footprint make these heaters less likely to get knocked over.
  • Easy to move around. Most models come with wheels and handles for easy portability.
  • Continue heating after being powered down. The unit will continue to give off heat for hours, even if unplugged.

Of course, there are also some drawbacks to these heaters compared to other space heater options. These include:

  • They take time to heat up. Before they can begin warming the space, oil filled heaters need time to warm up all the oil. This can take 30 minutes to 2.5 hours, depending on the exterior temperatures and the size of the room.
  • Most efficient for long runtimes. Because they use the most energy during startup, these units are only efficient if you plan to run them for longer periods.
  • Cost a lot upfront. While they’ll save you money in the long run, these heaters cost more to purchase upfront than your typical electric heater.
  • Bulky. The multi-fin, tall build of these heaters means they take up more space than other portable heaters.
  • Harder to store. The size and shape of these heaters also make them more difficult to store during the summer.

Overall, oil filled heaters are a great option for heating individual rooms during the cold winter months. When run for longer periods, they use less energy and cost less to operate than most electric space heaters.

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Aaron is the founder of and Essential Home and Garden. With over 15 years of hands-on experience in home ownership, lawn care, and gardening, Aaron is a seasoned expert in areas like lawn care, DIY, HVAC, and pest control.

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