How expensive are electric radiators expensive to run?

With increasing energy costs, all forms of heating has become more expensive.

Now, more than ever, it’s important to understand how expensive an electric heater or radiator will be to run. Especially before purchasing or kitting out your home.

Essentially, you can see how expensive an electric heater is to run with the Following equation:

Energy used each hour, multiplied by your energy tariff per Kilowatt Hour. (Energy used x tariff per kwh)

However, the figures alone don’t paint the full picture on an electric radiator running costs.

When running costs are stated, they’re generally to market the product. Which is different to telling the truth.

I’ve seen statements such as “Running costs = 7p per hour” or “Costs 80p per day”. Which is misleading and are almost never true. 

Statements like these do not consider how a radiator will perform in the real word. The running cost is different for each circumstance.

Running cost depends on room size and the level of insulation. This affects how much heat is needed to warm the space but also how much of that heat the room will lose. In addition, the deciding factor is how much you pay for your electricity. (Your tariff per kwh)

The radiator’s running costs can vary due to the conditions in the room. (As I will explain later)

The volume the room and level of insulation determines how much power (wattage) is required. (If you are unsure on what wattage radiator you need, see the link here.)

A radiator can only consume the amount of power it is rated to.

For example, a 1000w radiator can consume a maximum of 1kw each hour.

If we assume the energy tariff is 15p per kwh. The 1000w heater could consume a maximum of 15p each hour.

This assumes the heater is supplying heat for the full hour.

However, this is unlikely to happen. Once the room reaches the desired temperature, the radiator will switch off.

When the radiator is not supplying heat, the the consumption is barely noticeable. Naturally, the less time spent heating, the cheaper the heater will be to run.  

If we continue with previous example, If the radiator only spends half an hour heating that figure would be halved to 7.5p and so forth.

How well the room retains the heat determines how often the heater will have to be on for.     

This principle applies for every heater, whether it costs £100 or £1000.

The room and stimuli has a massive impact on the radiator. Which is why running costs can differ so much from one house to another.

Factors which can impact the running costs include:

  • The building’s U Values
  • The level of insulation
  • The volume of the room
  • The outside temperature
  • The internal resting temperature

More insulation will lower the room and building’s “U Value”. A lower U Value means less energy is needed to keep the room warm. As a result, the running costs will be lower.

As these factors can vary so much, its easy to see why an absolute figure for running cost cannot be quoted in the radiator’s marketing.

With the last paragraph in mind, even in the same room, the running cost can change through out the day.

Heat inside the room is constantly exchanging with the external conditions. This can affect the room in 2 ways:

  • Heat from the room will transfer into the external environment
  • Heat from the external environment will transfer into the room

As a result, when external conditions are colder (such as overnight) the room will be naturally cooler. When the external conditions are hotter (such as during the day) the room will be warmer.

When external conditions make the room warmer naturally. Less energy is needed from the radiator.

For example, if you set the radiator to 20 degrees. The room will reach this temperature faster if the ambient temperature is 17 degrees, than if the ambient temperature was 7 degrees. Basically, the radiator will spend less time heating and more time switched off.  

With this in mind, for initial hour of heating will have higher running costs. For the first hour, the radiator is increasing the temperature.

Then for the hours that proceed, the radiator is maintaining the temperature. Maintaining the temperature should require less energy and as a result the running cost will be lower.   

We’re asked “what is the energy rating”. 

Electric heaters do not have efficiency ratings in the same sense as other appliances (such as TV’s or Fridges.)

If you see an electric heater or radiator advertised as A, A+, ignore it. This type of rating does not apply to electric heaters.

This is because electric radiators are direct acting appliances. The electricity consumed is directly transferred into heat.

By design, there is very little else for the energy to be used on. (Other than the display or lights which account for less than 1% of the consumption.)

From the perspective of energy transfer, all electric heaters are around 99% efficient.

Whereas with a light bulb (for example) 80% of power is used to illuminate the light and 20% is wasted as heat. For this reason A,B,C ratings don’t apply to electric radiators heaters.

The only rating which applies erplot20 compliance. (Read more on LOT20 here)


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