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With energy costs at the top of most people’s worry list, you’re not alone if you’re trying to find ways to cut electricity use at home.

But if you’re trying to do that by using shorter dishwasher and washing machine programmes, you’re almost certainly adding to your electricity bill instead of making savings.

If you’re looking for money-saving ways to run your home appliances, there’s an ally that you might not have considered: the engineers who designed and built them.

For appliance manufacturers across the board right now, the number one challenge is to deliver more energy-efficient appliances.

And if your washing machine or dishwasher was bought in the last few years, chances are it’ll work differently to the machines you had 10- or 15 years ago. It’ll be much more energy efficient, too, but to harness the energy savings that they provide, you’ve got to use them in the right way.

My mother-in-law recently bought a new washing machine and was extremely worried when she discovered that its programmes last much longer than those of her trusty old appliance. She ended up stopping an ‘eco’ washing programme that she felt had been running for too long, and swapping to a fast wash, convinced that she was saving herself money.

But the opposite is true.

We spoke to Samsung Executive Vice President Moohyung Lee, Head of the brand’s Research and Development team for Digital Appliances. He explained how the company’s machines are becoming more energy efficient: “By cutting out heating, we can cut out a lot of the energy needed for a washing machine. But the washing time will be a little bit longer because we are just using cold water.”

In fact, Samsung claims that its forthcoming AI Ecobubble washing machines use a whopping 70% less power. (How? They use a mix of technologies: including a bubble generator and digital inverter technology that responds to sensor information to choose the optimum settings for the load.)

It isn’t just Samsung appliances, of course. All washing machines and dishwashers use most of their power to heat up cold water. So, what’s most efficient is to use less water overall and not to heat it up as much. And that’s how eco modes work. They use 35-59% less energy than a hot wash. But that means a longer running time to get the same cleaning power.

For example, the eco mode on Hisense’s HV651D60UK dishwasher takes well over three hours, which is over ten times as long as its fastest wash, and around three times as long as the standard cycle.

In fact, fast wash programmes exist purely for your convenience. You should only use them if you need clean clothes or dishes in a hurry. These programmes use more water and will heat it to a higher temperature to get the load clean quickly – but it’ll come at a cost of more energy use. Which of course means a higher electricity bill.

Emma is Home Tech Editor at Tech Advisor. She covers everything from kitchen appliances to smart home devices, from floor care to personal care to air care technology. She’s particularly interested in environmentally conscious brands and products that save people time and money.