Money expert Martin Lewis has officially weighed in on the debate about whether you should leave the heating on all day or switch it on only when you need it. The question has followed him for years, and as forecasts predict energy bills could rise by as much as 24% in January, he has now put out an energy bills special addressing common questions and myths around cutting gas and electricity bills.
What Martin Lewis said on the show
In the episode of The Martin Lewis Money Show Live on ITV1 on Tuesday (November 10), Martin Lewis was asked whether it is cheaper to leave the heating on all day or switch it on and off as needed. 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 9 in the morning, and then you have it on 4 to 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."
But Martin said that the reality is a lot more complicated than this, and it comes with some "big buts". He added: "Now we get to the baboons, the big buts. That’s sort of an easy default but it’s a lot more complicated."
Expert explains why it depends on your home
Prof Richard Fitton, Technical Director, Energy House Leads, was a guest on Martin's show and set out how the type of house you live in and what it's built with can massively change 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."
Martin replied: "So the first one, you have it on low and slow all day?" He 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. I’d say if you took a typical winter week so maybe some time in December, that will answer your question."
Energy Saving Trust and MSE advice
The Energy Saving Trust says that if you have a boiler (and most still do, even though heat pumps are becoming more common), then the best thing to do is turn your heating on and off, not leave it on all 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’s more energy efficient, and better for your bills, to have your boiler come on when you need it."
But if you do have a heat pump, then leaving the heating on all day is better. 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 points to the 'low and slow' method, which works best with modern boilers. Here, you set the boiler to a lower constant temperature rather than turning it on and off all the time. Setting it to 18C or 19C and then leaving it on constantly can help the boiler to recover waste heat and operate 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."
