The advantages of electric heaters are their ease of use, low purchase price, low maintenance and mobility. They are the most common supplement for the primary heating system of an apartment or a house, and they are often used in rooms without heating.
However, such additional heating could also have its downsides when it comes to the running cost.
The biggest drawback is the poor ratio between invested and received energy. While the efficiency of electric heaters is almost 100%, their thermal efficiency is still considered modest compared to heating systems like heat pumps, which can have a ratio of invested vs. received energy of 1:2, 1:3, 1:4 or more.
Depending on where you live, electricity could be the most expensive energy source, but still, electric heaters are very convenient and practical.
If we know how to calculate the cost of running a space heater for an hour, a full day or a month, we could use it more rationally and avoid any suprises when we receive the monthly electricity bill.
How to find out how much power your heater needs?
Power rating of a space heater can be found on a tag containing specifications. It's usually near the electric cord, on the side or on the bottom side of the housing. The power rating will be displayed in watts.
Other ways to find out the power rating is by checking the box the heater came in, by checking the user manual or finding the same product online and looking at the specifications.
Calculating the running cost of an electric space heater in theory
Since most space heaters on the market use on average 1,500 watts, we'll use that amount of power as an example for our calculation.
First, we divide the power of the heater in watts by 1,000 to get kilowatts. In our example case, a 1,500 W is equal to 1.5 kW. If a space heater has 2,000 watts - that's equal to 2 kW.
Then we simply multiply it by the price of electricity per kilowatt to get the cost of running a space heater for an hour.
Power of the heater (kW) * Price of electricity ($ per kWh) = Cost to run a heater ($ per hour)
Electricity prices are different in every country / state, so we'll use $0.166, which is currently the average electricity price per kWh in the United States.
Using the above formula, it's now easy to calculate how much it'll cost us to run a 1.5 kW space heater for an hour.
1.5 kW * 0.166 = $0,249 / h
To get the cost of running a space heater for a full day, we need to multiply our running cost per hour with the amount of hours we run a heater in a day. Let's say we use a space heater to heat a roomfrom 7 am to 7 pm. If the heater is running for 12 hours per day, it would cost $2.98. Keep in mind that this theory assumes that the heater is constantly running during a timeframe of 12 hours.
$0,249 (cost per hour) * 12 (hours) = $2.98
To run a space heater for 24 hours, in theory, it would cost around $6.
$0,249 (cost per hour) * 24 (hours) = $5.97
But wait, there's a catch!
We must admit, it's pretty funny to read articles all over the internet about electricity consumption of various appliances. You'll notice most sites say that if a refrigerator consumes 100 W per hour, it must consume 2,400 W per day!
Sure grandpa, let's get you to bed.
What they almost always fail to notice is the fact that a fridge does indeed consume 100 W per hour, but only when running. When it reaches the set temperature, the compressor will turn off and stay that way for a certain period of time until it goes into another cycle and turns on again. This means that it will effectively run 20% of the time, or less (depending on various factors).
The same thing goes for your TV. It consumes electricity only when turned on. And, you've guessed it - the same logic goes for space heaters too.
Electric space heaters don't run 100% of the time
Fan heaters, convector heaters, oil-filled radiators, ceramic or infrared heaters - they all have one common feature - overheating protection. While it's often marketed as a premium feature, it's a pretty simple feature and in fact a crucial one if you don't want to get your house or an apartment burnt down.
When you turn your heater on, it will run for some time before the heating element gets so hot that it needs to be turned off to prevent the possiblity of overheating. For this reason alone, it's fair to say that if you leave your heater on for an hour, it'll only work about 50% of that time - and in fact consume 50% of electricity from our previous calculation. The percentage varies based on a number of factors such as the room temperature, type of heater, etc.
There's also another obvious reason a heater won't run 100% of the time - room temperature. When you wake up to a cold room and crank up that heater, it'll have to work harder to reach the desired temperature. Let's say it'll work 50% of the time.
But how much will it consume when it warms up the room? Much less. Again, depending on a number of factors; the most crucial one being heat loss of your room. The less your room loses its heat, the less your heater has to work.
So, if you've had your heater on for 8 hours, the room is pretty warm by now and your heater might work only 20% of the time to maintain the set temperature.
We've tested this ourselves. While writing this article, our 2 kW (or 2,000 W) oil-filled radiator spent 1 kWh. Why didn't it spend 2 kWh? Because it only ran 50% of the time, or to be precise - the thermostat went on and off during one hour and made the heater run for 30 minutes inside a 60 minute time frame.
Don't believe us? There's a way to measure the consumption yourself.
The most accurate way to measure space heater running cost
Use a cheap device called a wattmeter. As a test, turn your heater on for an hour and the wattmeter will show exactly how many kilowatt-hours are spent.
You can then try plugging in various space heaters and compare their consumption vs. how warm the room felt. Run it for the whole day and you'll have your real-world calculation of the cost of running it for a day, and whether it ran 70%, 50% or just 20% of the time.
You might be suprised to see the results.
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