At this time of year, you’re bound to come across a lot of articles that tell you how much an electric heater costs to run, compared to a gas boiler. Yet, many articles get the basics wrong, and you need to make sure that you’re comparing the right figures.
Simple calculations are dumb calculations
Gas and electricity are priced per kWh of use. Currently, gas is 6.29p per kWh and electricity is 26.53p per kWh.
Using the simple calculation, the cost to run an electric heater per hour is its energy consumption in kW multiplied by the cost per kWh. So, a 2kW electric heater costs 53.06p per hour to run.
Then, you see a lot of people try to apply the same logic to boilers. They’ll look at the headline specs and see that boilers are typically rated between 20kW and 40kW. Using the same calculation, only with gas prices, you get a running cost of between 125.8p and 251.6p per hour. Ergo, goes the dumb calculation, an electric heater is cheaper to run than a boiler.
Only, these calculations are nonsense, particularly for boilers.
Modulation is key
Boilers use modulation, which is the ability to adjust the heat output to match the actual demand.
With a boiler’s flow temperature set correctly, the actual heat demand to start with is much lower than the boiler’s maximum rated output, and once the radiators are hot, the boiler needs to expend even less energy to maintain the correct flow temperature, so gas consumption goes down.
A boiler’s rating is its maximum consumption, and you’d have to have water temperatures set to maximum and a high water flow rate to see that. For most situations, the boiler won’t be operating anywhere near its full capacity.
Cost per hour is unhelpful
As you can see from the boiler example above, modulation means that the boiler output is not constant and there are a lot of other factors at play: how many radiators are on, the outside temperature, the level of insulation you have and so on.
Basically, a boiler doesn’t have a consistent running cost per hour, and gas consumption will change with actual demand.
Likewise, a good electric heater will have a thermostat that will turn the heater off when the right temperature has been reached. So, although you might have an electric heater turned ‘on’ for two hours, say, the heater may only actually be drawing power for a fraction of this.
And, there’s no point in comparing the hourly running cost of two heaters rated at different power levels. A 1kW heater costs half as much per hour to run than a 2kW heater, but it will take twice as long to warm the same space.
Rather, it’s the heat output required to warm a room or your house to a target temperature that’s the important factor.
As discussed previously, there’s no cheap-to-run electric heating; however, if you need to heat a single room, then an electric heater may be cheaper than turning the central heating on, but central heating is cheaper than using electric heating throughout your home.
