Energy mythbusting

Common energy myths solved

With energy bills still extremely high, using less energy is a key way to cut bills, and there are obvious ways to do this, such as turning your lights and heating off when you're out. But this guide aims to crack the less-obvious energy conundrums, such as whether it's better to leave your heating on all day and if it's worth turning devices off standby mode.

Key energy saving guides

Energy mythbusters

In this guide, we debunk some common energy saving conundrums.

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The big savers to cut your energy bills.

Tips to keep yourself warm for less.

Energy saving myths (and how we've debunked 'em)

There are a lot of urban myths and "quick tricks" for saving money on your energy bills. Many are a bit rubbish but some do offer simple and cheap ways to reduce your energy usage (and your monthly bill).

We've rounded up some of the most common energy saving myths and misconceptions below. As we're experts on MoneySaving – and not the intricate science behind using less energy – we've sought advice from the specialists at the Energy Saving Trust, and other experts for the more techie questions, including British Gas and an independent plumber, while also finding out what MoneySavers on Facebook, Twitter and the MSE Forum had to say.

As is often the case in the world of science, not everyone agrees on every point so there isn't always a definitive answer, but our research should hopefully help you make an informed decision.

1. Is it cheaper to leave the heating on low all day or only turn it on when I need it?

We wish we could give you a definitive answer, but this question is far more complex than it first seems and we're not heating engineers or physicists. So please ignore clickbait publications erroneously crediting Martin with an answer – he knows a lot (too much) about energy bills, but this one isn't his or our bag.

Ultimately, there are arguments for and against it, and it'll likely depend on the type of heating system, your usage pattern, and what type of home and insulation you have.

The 'Official Answer' – leaving the heating on all day leads to greater heat loss and means higher cost

The main UK public body for reducing energy use and carbon emissions is the Energy Saving Trust. Its formal answer is that leaving the heating on all day consumes more fuel, leads to greater heat loss, and that means higher costs.

The concept is simple: pump heat into your home when you need it; don't pay to keep pumping it when you don't. It says this is the best way to save energy and money (using a timer's best, so your thermostat turns your heating on and off to keep your home at the temperature you want).

The '(Un)Official Opposition' – condensation and boilers matter

- Got a modern boiler or heat pump? Slow and steady heating could be more efficient...

Heat Geek, a help service which gives advice on heating, offers training services and installs heat pumps, says it's much more complicated than this. It argues that if you spend a decent amount of time at home (all evening and weekends), even if not there all day, every day, you could be better off leaving the heating on constantly if you have:

a) Heat pumps: A low-carbon form of electric heating which captures heat from outside the home.

b) A modern condensing boiler (installed since 2005): These recover some waste heat before it's lost.

Rather than turning it on and off, it could be more efficient to lower temperatures to around 18 or 19°C and keep it on (you could increase slightly during the day if you're cold, but don't let it dip below this) and have as low a 'flow temperature' (radiator temperature) as you can safely – it'll mean your heating system won't be as responsive, but as it's on constantly, this won't be as big an issue.

Heat Geek calls this the 'low and slow' method – low temperatures and slow heating responsiveness – and it says this means the boiler can recover more waste heat and so operates more efficiently, which it thinks will outweigh the cost of heat loss from having it on all day. It says there are other variables to consider though, including:

  • Not in a lot? If you're out all day, every day, and often go straight to bed when getting home, then heating throughout the day would be wasteful.
  • Newer plasterboard walls are quicker to heat up. Modern plasterboard walls are quicker to heat up, so turning off the heat during the day may be a decent option. Yet older brick buildings will likely take longer to warm up, but will release heat back in, so low and slow is good here.
  • Do you have radiators and/or underfloor heating? Radiators are more suited to on and off heating; underfloor to constant heating.
  • What insulation do you have? If you have cavity wall and loft insulation up to modern standards, then low and slow would work better as you'll lose less heat. If not, on and off heating might be better. (Also, see if you qualify for free insulation.)

- Some argue you should keep the heating on constantly for an entirely different reason...

Here, the argument is that keeping the heating on low all day, turning all radiator valves up to the max and the boiler down to the minimum will prevent condensation collecting within the walls each time the heating is turned off. This condensation can help to conduct heat outside the home – meaning you lose heat more quickly and use more energy as a result.

Some councils also recommend this to prevent damp and the growth of mould.

- Oh come on MSE, that didn't help – I still don't know what to do...

We get, and share, your frustration. Sadly there doesn't seem to be a firm answer. Hopefully the info above will tell you which is a good starting point for your circumstances.

So perhaps the best advice is 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. Though of course if you're comparing a particularly cold week with a fairly mild one, it'll skew the results. And please let us know how you get on.

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2. Should I put clingfilm on the windows?

Although clingfilm is normally used to wrap up your sandwiches, it may actually help keep your home warm too.

Although not technically clingfilm, the Centre for Sustainable Energy suggests covering windows with a thin transparent plastic film, which looks like clingfilm, and you can install yourself. It's cheap and simple, and by putting a sheet of specifically designed film (or good old fashioned clingfilm) on each of your windows, you trap a small layer of air, which can help to stop heat from escaping. The key for adding a second layer of 'glazing' is that it's transparent and airtight.

While clingfilm works in theory...

Ideally you'd want to install specialist secondary glazing as it'll last longer. If you have double glazing, adding a third layer could make you a little warmer, but the benefit will be much less noticeable than with a single-glazed window.

If your windows are draughty, it's worth fixing that as well as adding secondary glazing, or you'll only get half the benefit.

3. Do devices on standby or chargers left in sockets still use electricity?

Yes. British Gas says that chargers and appliances will still use electricity when left in sockets – so it's important to turn them off at the plug when you're not using them. 

A lot of devices, such as games consoles, laptops and TVs, draw small amounts of power when not in use but still plugged in and turned on at the socket. This is sometimes known as 'vampire power'. You can easily avoid using this standby power by switching devices off at the wall.

The Energy Saving Trust says you can save about £55 a year by turning off your appliances at the plug when you're not using them.

However, it's EU law that TVs and other devices made since 2013 can't use more than 0.5 watts in standby mode. To show the scale of it, a TV left on standby for 20 hours a day would cost about £1 a year. So while you may not save as much as the Energy Saving Trust says, it can still be worth doing – all devices will still use a small amount of power, and this can add up.

4. Will smart meters save me money?

No – at least not on their own.

Smart meters simply replace your existing gas and electricity meters (one for each), keep track of your usage and automatically send meter readings to your supplier each month.

However, they can help you to identify ways to save energy via their in-home display. This small gadget communicates wirelessly with your smart meters, monitoring what energy you're using and showing you how much it costs, in near real time.

With more information on your day-to-day energy use, you'll be able to spot ways to cut back. For more, see our Smart meters guide.

5. Should I run appliances at night?

This will depend on who supplies your energy and your tariff. If you're on an Economy 7 or 10 tariff, (also with some specialist EV tariffs), you'll pay less for energy you use during the night, but a higher rate than average during the day. If you're on another tariff, you'll pay the same amount regardless of what time of day it is.

If you're unsure what tariff you're on, check your latest energy bill or ask your energy company.

Important. Before you use an appliance at night, check it's safe. For example, the fire service says you should never run the tumble dryer while you're asleep, as it's a common cause of fires in the home.

6. Would painting my radiators black help?

Where painting your radiators black is concerned, the answer's no, according to the Energy Saving Trust. It's best to keep them the standard white, although the difference is not huge. 

MSE Forum feedback: This answer was disputed. Some say black is a more efficient colour at absorbing and then giving off heat, while others say that by painting a radiator, the paint itself can act as an insulator. This means less heat is transferred to the room.

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What about radiator panels?

Radiator panels can save energy, but not very much. It's more important that your walls are insulated, to prevent the heat leaking out of your home altogether. See The Great British Insulation Scheme guide for more information. 

As for putting reflective panels behind radiators, yes, the Energy Saving Trust agrees that these could help cut energy use. They reflect heat from the radiator back into the room, so it doesn't escape through external walls. The trust says homes with uninsulated walls will get most benefit.

7.  Is it cheaper to use an electric heater rather than a radiator?

Electric heaters are efficient at converting energy into heat, and can be a cost-effective solution if you're heating just one room for a short period of time. They give off heat immediately, but equally, as soon as you switch them off, the heat disappears. If you're heating a larger space and want it to remain warm for longer, you'll likely be far better off using central heating. 

There are lots of different types of electric heater (convector, halogen, fan, to name a few), but a typical one uses around 2,000 watts. At current Price Cap rates, it would cost you 58p to have one on for an hour. In comparison, a typical 24-kilowatt gas boiler and radiator system would cost about £1.78 an hour.

Yet while electric heaters are cheaper, they don't tend to heat the space inside your home as efficiently. So if you're just heating yourself for an hour or two, an electric heater can be a more cost-effective way to warm up, compared with firing up your whole central heating system.

But if you want to heat multiple rooms, or one room for longer periods of time, your central heating is likely to be more efficient.

You also need to factor in how well insulated your home is. One that's poorly insulated will let heat escape easily, so you'll be throwing money out the window. Turn draught detective and add extra insulation in your loft to prevent heat loss.

8. Should I leave lights and appliances on, or turn them on and off each time?

The Energy Saving Trust recommends turning off lights when leaving a room, regardless of how long for (and being mindful of how many lights you have on at any one time). Also, avoid leaving TVs and other devices on standby.

MSE Forum feedback: While turning devices off completely saves energy, the difference can be negligible. So don't bank on this solving all your energy woes.

9. Should you leave your heating on if you're going away?

Yes – in the winter. To prevent frozen pipes, which can cause £100s of damage, the Energy Saving Trust recommends you leave the heating on to some degree during winter, even if you're not there.

Check your home insurance policy before you go away. The general rule is to keep your heating at a minimum 12°C (but some say at least 15°C), rather than switching it off completely.

10. If my heating is on, should I keep my internal doors open or closed?

It's better to keep the doors of rooms that you don't want to heat closed, says the Energy Saving Trust.

Radiators, electric panel heaters and convection heaters all work by creating a convection current in a room. As hot air rises, it circles around to the other side of the room, cools and sinks, and travels back along the floor to the heater to be reheated again.

Closing doors makes sure this current remains within the designated space, and stops cold air from getting in.

11. Is it cheaper to boil water in a microwave?

With kettles being power-hungry appliances – using up to 3,000 watts – you may look to alternatives to boil water for your cuppa. We did a quick number crunch to find out which is cheaper: boiling water in a kettle or a microwave.

Method Power rating (watts) Time to boil Cost of electricity (1)
Microwave 1,120 watts (gives output of 800 watts) 2 minutes 30 seconds 1.4p
Kettle (2) 3,000 watts 1 minute 1.5p

(1) Cost based on January's Energy Price Cap rate of 28.62p a kilowatt hour. (2) Kettle filled with one mug of water.

In our small experiment, boiling a mug of water in a microwave was slightly cheaper than boiling it in a kettle, though there's not much in it.

Although it's technically cheaper to use a microwave...

Electrical Safety First warns that boiling water in a microwave can be dangerous as you could overheat the water past boiling point and cause it to explode. On the other hand, a kettle is designed to switch off once it reaches boiling point.

When using a kettle, it's also more economical if you only boil what you need. The Energy Saving Trust reckons you could save £11 a year this way compared with overfilling it each time. See our Energy saving tips and Cut your water bills guides for more.

12. Is it expensive to run an electric fan?

Many have asked us if using an electric fan to keep cool in summer will burn a hole in their pocket. 

The good news is you CAN use an electric fan to manage the heat without breaking into a cold sweat at the cost.

A typical 12-inch 35-watt desk fan would cost around 1p an hour to run based on the current Price Cap rates, so about 8p if you leave it on all night. A big 50-watt tower fan wouldn't cost much more – about 1.5p an hour. If you have a large floor fan, they typically range between 10 watts and 120 watts, costing up to 3.5p an hour. 

13. Should I keep the hot water boiler on all the time, or turn it on and off as needed?

If you have a gas, oil or LPG (liquefied petroleum gas) central heating system, the experts say it will always be cheaper to set the system timer so the hot water comes on only when you need it. If you have a combi boiler, you can also make savings by lowering your hot water temperature – about 55°C should be enough for most households, according to Octopus Energy.

However, if you use an electrical immersion heater and have an Economy 7 or 10 tariff (where energy is cheaper at night), it's cheaper to heat your water during the night. You'll need to make sure your tank is well insulated to prevent it cooling during the day though.

If you're unsure what tariff you're on, check your latest energy bill or ask your energy firm.

14. Do solar panels work in winter?

It's a common misconception that solar panels don't function during winter or on cloudy days. While they are certainly more effective at generating electricity when it's bright and sunny, solar panels can still produce electricity on the greyest of days – good news for us Brits.

It's about daylight, rather than sunlight. Even in overcast conditions, there's still some sunlight filtering through the clouds, allowing your panels to generate electricity, albeit less effectively.

Snow and ice directly on your solar panels can also reduce the power output. But modern solar panels are designed to be self-cleaning to some extent, so the reduced output should be temporary.

We've got lots more info in our Solar panels – are they worth it? guide.

If you've got any other burning energy questions you'd like answered, please suggest them in the Energy mythbusting forum thread.

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