Martin Lewis has addressed the long-running question of whether it is cheaper to leave the heating on all day or only switch it on when needed. The money expert released a dedicated energy bills special on his ITV show, tackling common myths about cutting gas and electricity costs, amid forecasts that energy bills could rise by as much as 24% in January.
Energy Saving Trust Default
During The Martin Lewis Money Show Live on ITV1 on Tuesday (November 10), Lewis was asked whether it works out cheaper to leave heating running all day or to switch it on and off as required. He said: "What I would start by saying is the Energy Savings Trust default setting is that you have your heating on from 7 to 9 in the morning. This is people who go out to work all day, not people staying at home all day."
He added: "You have your heating on, til nine in the morning, and then you have it on 4–11 in at night, and that should keep the fabric of your house going and generally the rule is you only pump heat into your house when you need it, and then you don't put it on when you don't need it and put it on again when you need it."
However, Lewis warned that the reality is more complex, describing "big buts." He said: "Now we get to the baboons, the big buts. That's sort of an easy default but it's a lot more complicated."
Property Type Matters
Prof Richard Fitton, Technical Director, Energy House Leads, appeared as a guest on the show, explaining how the type of property and its materials can alter the answer. He said: "I'm going to be the disappointing person who says 'I don't know the answer'. Because it really does depend."
He continued: "It depends on a number of things, the weather, the type of building, if you've got a big heavyweight house with lots of thermal mass. It might be a solid brick Victorian terrace for instance. And that will store heat and act as a battery for heat. Whereas if you have a very lightweight or modern house made of timber frame for instance, that will heat up really quickly but won't necessarily store the heat."
Lewis replied: "So the first one, you have it on low and slow all day?" Fitton answered: "They can work in different ways but I think that's probably an easier challenge for that house. But the simple answer to this is more than 60% of people have smart meters. You can literally do your own experiment. Put me out of a job, do your own scientific experiment and see which works out best for you."
Boilers vs Heat Pumps
The Energy Saving Trust advises that if you have a boiler, the wisest approach is to switch your heating on and off as needed, rather than leaving it running throughout the day. It said: "If you have a boiler, then no - keeping your heating on all the time will use more energy and cost you more money."
It added: "It's more energy efficient, and better for your bills, to have your boiler come on when you need it." However, for those with a heat pump, leaving the heating on throughout the day is the better option. It adds: "But if you have a heat pump, then you can save money by leaving the heating on all day. Check out our advice on how to improve your heat pump's efficiency."
Martin Lewis' MSE says that there are arguments "for and against it." MSE highlights the 'low and slow' method, which works best with modern boilers, involving setting the boiler to a lower constant temperature rather than switching it on and off throughout the day. Setting it to 18C or 19C and leaving it running continuously can help the boiler recover waste heat and run more efficiently.
MSE adds: "So perhaps the best advice is to try an experiment. Try a few days or a week with your heating on a constant low setting and then try only having the heating come on as and when you need it over the same time period and compare the energy use. Take meter readings at the start and end of each period and compare."
