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Heatwave – How much electricity does a portable air conditioning unit use?

Heatwave! Temperatures are set to soar yet again, with forecasters predicting record highs – another summer in which keeping cool is a problem!

There has certainly been a rush for fans in the shops this year, with portable air conditioner units becoming the ‘must-have’ item this summer to cool an office or your home. So how do they work? And more importantly how much do they cost to run?


An air conditioner works in the same way as your fridge, cooling your room by passing warm air over a cold evaporator coil, and then blowing cooled air into your room.  This process also generates hot air that needs to be vented out of the building by an exhaust hose, usually placed through a window. Another often forgotten element of this cooling process is that it generates water and dries the air, that’s why portable air conditioning units have water tanks that need to be emptied.

How do I keep my room cool and my air conditioning unit running efficiently?

Carrying on the fridge theme… if you think of your room as a fridge, the last thing you’d do is leave the fridge door open, the same applies to the room you’re trying to cool. Keep your space well sealed by closing doors and windows, this will ensure you get the best out of the air con unit. Closing blinds and curtains will reduce the heat from sunshine through windows and doors. Good levels of insulation will help keep rooms cooler in summer, as well as warmer in winter.  Hot summers may be a rare experience for the UK, but travel to Europe – France, Spain, or Italy and you’ll find plenty of external shutters preventing the sun’s heat from entering the room.

What do you look for when buying an air conditioner?

A thermostat is pretty crucial!  You don’t want to waste energy trying to get your room too cold, and a timer is a good bet also.  Like other electrical appliances, air conditioners have energy efficiency labels, graded from A to G for energy efficiency; go for the best you can afford and save long-term. Washable pre-filters and odour-eating carbon filters are useful features.

Electricity Cost Calculator

How much do they cost to run? Just check the power consumption figures, then use Sust-it’s energy cost calculator to see what that will cost to run per hour.  Click here to see the potential air conditioner running costs.


Air Conditioning Units ranked by annual running cost

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Reluctantly, I’ve given up on long-distance electric vehicle journeys

Like most drivers, the majority of my car journeys are relatively short. Meetings, deliveries, trips to the shops, ferrying children around, going to friends and family. For these journeys, an electric vehicle (EV) is brilliant. Particularly as we’ve off-road parking and charging at home.

Over the past six years, electric vehicle ownership for myself has been good for my wallet and the planet (hopefully!). Even long excursions were possible with planning, a handful of charging network membership cards, and a phone full of EV charging apps!

Electric vehicles, victims of their success

Now, electric cars are becoming mainstream must-haves for company tax-efficient motoring — or those looking to reduce their carbon footprint. The economic argument evolves even more with fuel prices going through the roof. Those who have no interest in NetZero or carbon reduction are looking at going electric, and why not? They are excellent to drive and cheap to run if you’re charging from home on off-peak electricity. Just think of all that money you’ll save to spend on short-haul flights and patio heaters!

Range anxiety, no, it’s charger rage!

Range anxiety is no longer the primary concern; now it’s finding a charger that hasn’t got a plug-in hybrid in it! Why do drivers who have a perfectly working internal combustion engine still feel the need to plug in their vehicle? Then there’s the; I’m nearly fully charged, but they still feel the need to top up their EVs and leave it charging for hours whilst shopping! Finally, what happens when you’re on a long journey in a pure electric car… should you hang around to see if the driver turns up? Especially when you’ve got ten miles left in the battery. Do you risk driving five miles up the road to see if there’s a charger free? Can you trust what the EV charger app map is telling you? If you get there, will there be a row of SUVs, which all look the size of buses — I thought lighter and aerodynamic vehicles were more efficient, stacking up for the next charging slot.

And this is when you’ve rerouted because the motorway services charging network is inadequate. Is this because the electricity infrastructure is in the wrong place? Or that the monopoly players are holding on to their assets?

Long journeys turn into nightmares very quickly

The upshot, a journey that should take three or four hours, takes seven or eight! Sorry, I’m late for the meeting. Could we reschedule for tomorrow morning whilst I find a free charging space? 

Even a trip to the Capital, which appears to have chargers everywhere, turned into misery. It took over two and half hours to find (A) a charger that worked or (B) one that let non-residents use it. Even spotting the charge points isn’t easy; why not have standard signage highlighting their whereabouts? It’s incredibly stressful when you have a deadline and goods to deliver.

Electric cars make fantastic runarounds

The reality of EV ownership is very mixed; yes, they make competent second cars for dashing around, especially if you’ve off-street charging. On the other hand, lengthier journeys are achievable if you can afford an EV with a tonne of batteries. It seems counterintuitive; why lug a mass of weight everywhere for that infrequent longer trip — how can that be efficient?

Ten times more en route, rapid chargers are required to support long-distance journeys

An independent report from the Electric Vehicle Energy Taskforce has forecasted a whopping 500,000 public charge points need to be deployed by 2035. (Currently, we have 30,000 in 2022). To give drivers the faith to buy electric vehicles and the means to charge them. Half of these (250,000) will support drivers in homes without off-street parking. However, will it be feasible to let the market sort out the charging infrastructure? What’s the commercial incentive to install street chargers that only deliver 3 or 7kWh per hour if income is only 50p per unit of electricity. That’s £1.75 to £3.50 an hour before you’ve even paid for the wholesale electricity. Not to mention installation expenses, upkeep and real estate expenditures.

Electric car driving cost advantages will diminish over time

The price advantage of EV driving will take a hit, too, with the report highlighting that household charging prices will be 25% higher without smart charging — and that’s before road pricing kicks in. In addition, the cost of en-route charging is escalating at the moment, with some networks charging £0.71 per/kWh, compared to the energy price cap of £0.28p per/kWh, or home smart off-peak charging tariffs at just 8p per/kWh

The EV charging network is improving rapidly, though nowhere near quick enough to keep up with demand. Hence, I’m looking for an alternative for those longer drives until the charging grid improves.

What should policymakers do to make travel greener?

It’s a chicken and egg situation — if you encourage electric car ownership and wait for the infrastructure, you’ll risk frustrating drivers who’ll turn back to conventional combustion engines. But conversely, it will be a lengthy wait for the infrastructure as the grid can’t currently cope with the growing demand for electric charging. So, put more resources into public transport, cycling-friendly options and encourage car sharing, particularly in urban areas. Learn lessons from the pandemic — encourage flexible working and fewer car journeys as the greenest option. And don’t hoodwink the public that simply buying an electric car will be easy!

How to find the best energy saving washing machines, tumble dryers, fridges and electricals – whatever your budget

There seems to be no getting away from it that the most energy efficient washing machines, tumble dryers and refrigeration products tend to be expensive. Premium brands such as Miele, LG, Panasonic, Siemens, Liebherr and AEG certainly top our efficiency tables. Saying that, there are some great midrange and budget appliances and electricals out there. However, finding these isn’t that easy, as energy labels don’t highlight the real costs of running appliances. That’s where Sust-it’s Green Plug Score can help you find the best energy saving appliances, whatever your budget.

What is our GreenPlug score?

To help you find the most energy efficient products we’ve introduced a new ‘Green Plug Score’ percentage. This compares ALL products within our database giving them a score out of 100. The best products available in the marketplace score 100%, and the worst score a measly 1% – it’s these low scoring, energy hungry electricals that are best avoided!

  • 100% – This is the most efficient in the marketplace
  • 50% – Average energy usage performance
  • 25% – Poor inefficient products

How to find energy efficient products on a tight budget?

Sust-it ranks products by their ultimate energy efficiency, based on their published energy labels, or manufacturer’s specification figures. This highlights most efficient products in any chosen category regardless of price. By using the select menus you can filter options down further e.g. by brand, or capacity if you’re looking at washing machines. These filters then rank products showing you the most efficient by a particular brand or it’s capacity.

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How much does it cost to run an electric car in the UK?

Having logged the electricity usage for two years and over twenty thousand miles, we can confirm that the savings from EV ownership are substantial when compared to petrol or diesel fuelled cars.

Our home charger was installed as part of a Government pilot scheme to assess the usage patterns of electric car owners. It’s been transmitting our energy usage back to Chargemaster’s databases since we leased our EV in 2017. The Mercedes 250e used during the test didn’t have a very good range and no facility to rapid charge. Hence, away from home charging wasn’t an option over the two years – making the figures representative of the overall running costs. The figures are based on an electricity tariff of 11p a unit in 2018 and 10.28p in 2017. Over this two-year period, we covered 21,618 miles at a cost of £0.05486 per mile. Making the running cost £1,186 for two years or £593 per year – which is remarkably near the running cost estimates on Sust-it.

Electric Mercedes 250e ownership experience

Please take a look at our video review.

Cost of running electric car vs petrol

Electric cars are considerably cheaper to run at the moment, as we’re being encouraged to convert from polluting diesel to petrol hybrids and pure electric vehicles. I’m sure these tax incentives will diminish once the government coffers are reduced as fuel duty tax returns drop. Our advice, if you can afford an electric car, is to grab yourself cheaper motoring while you can, or better still simply drive less! For company car drivers and business owners, the incentives are even more tempting. Check out our guide to EV ownership.


We did a comparison between a Nissan Leaf and a Skoda Citigo; this outlines the savings over an average week of motoring.

Calculating the cost of charging an electric car

As with many of things in life, there is no one simple, straightforward answer to this question – there are lots of variables. The biggest factor will be the capacity of the battery in your electric vehicle (EV) and what price you’re paying for energy. And of course, how much charge is left in the battery when it’s topped-up. The basic rule of thumb is the longer the range of your EV, the more it’s going to cost to fully charge.

Electric vehicles running costs

Manufacturers aren’t making it easy to identify battery capacity. They often quote models in kilowatts hours (kWh) or Amp-hours (Ah). Looking for the kWh of the vehicle’s battery is the simplest way to get a rough idea of its charging cost, as we buy electricity in kWh units. So, if you have a 40-kW battery that is completely empty (something you should never do, more on this in a future post!) it would cost 40 x your kilowatts hours tariff. Let’s keep it simple – 40 x 15p (kWh) tariff = £6.00 to fully charge the battery.

We’ve developed two handy electric car calculators that highlight the potential savings that switching to electric can have. Here’s our Electric Car Journey Cost Calculator and Petrol and Diesel Car Journey Calculator

Electric Car Journey Cost Calculator

How long should it take to charge an electric car?

Again, this depends on the variables – yet more complications – such as what your car can cope with in terms of energy input, and the charging unit/station you’re connecting to.

There are three types of chargers:

Rapid – Usually found at Motorway Service Stations and are AC (Alternating) or DC (Direct Current). Rapid AC chargers are rated at 43 kW. Rapid DC units are over 50 kW. These will charge most EVs to 80% in about 30-60 minutes depending on the battery’s capacity. Tesla’s Superchargers are DC and charge at 120 kW making them much faster!

Fast – Mostly found in supermarkets and car parks. These are rated at 7 kW to 22 kW and should fully charge an EV in 4-5 hours.

Slow – best for overnight charging, taking about 6 to 12 hours to charge a pure EV. Plugin hybrids (PHEV’s) should take less as they have smaller battery capacities. These are rated up to 3kW

Electric Car Reviews

Things to check before having an electric car charger installed 

Always check your vehicles charging rates. The Mercedes 250e we ran for two years could only be charged with slow or fast chargers. So no Rapid charges on the motorway, making long journeys a non-starter for this car – unless you fancy a 5/8-hour comfort break!  This car was even more complicated by the fact that it required a three-phase electricity supply (415v) to charge at any reasonable speed, even on a fast charger. Our home-charger was a 30A single-phase unit (240v), which works well with most EV’s.

More details on the practicalities of electric car ownership can be found here.

Is an electric car right for you?

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Smart tech – always listening, always on! “Alexa how much energy do you use?”

All homes have a background energy usage driven by the electricals that are on 24/7. Refrigerators, appliances on standby, set-top boxes, TVs, pumps, boilers, broadband routers, computers, chargers – the list of items sucking energy goes on and on!  Now smart devices… voice-controlled ‘smart speakers’ and home hubs have become the next ‘must-have’ tech. The irony is that this tech is consuming far more electricity than the old enemy – leaving stuff on standby!

Connected homes are being touted as the next big thing for those who have trouble typing, can’t find their remotes, or need help setting the timer on their heating! I hear myself now shouting “Hey Google! Siri! Alexa! Where’s my phone?” … “I don’t know… but I’ve found this on the web.”

Smart thermostat controls, making your heating work less

Whilst these devices may make life easier, and could potentially save you some energy if you’re using smart thermostat controls, like Google’s Nest or British Gas Hive products. Managing your heating as efficiently as possible it should get your bills down. These devices learn temperatures you like, then adjust automatically.  They’re controllable from smartphones, so if you’re delayed getting home you could remotely re-schedule your heating to come on later. Programming boilers on/off cycles should be much more user-friendly when done through an app interface. According to Nest’s own US research customers saved about 10-12% on their heating bills. However, I was quite surprised to see that the Nest thermostat uses 1kWh per month in standby.

Hive, owned by Centrica (British Gas) have claimed savings of £150 a year. These claims are really difficult to substantiate as it’s more about behavioural changes than the tech itself – turning down your heating a bit, wearing more clothes, or draft proofing your home could be equally effective. Combine this with switching to LED lighting, or upgrading to more efficient appliances, and you could easily match these claimed savings from installing their smart tech devices, without the expense.

Motion trackers helping disabled or older people, and those with health conditions

British Gas recently introduced a monitoring service that bolts onto the connected home Hive products. It’s available for a fee of £15 a month, plus a one-off £150 upfront charge. When installed a carer receives alerts via an app if anything out of the usual routine happens, such as a kettle not being switched on at the same time each day, or rooms not being entered. The monitoring is not meant as a replacement to everyday visits or contact, but as a safety guide to thousands of unpaid carers.

The Hive Link service does not have a camera; however, it does include motion sensors, window and door sensors, plus plugin sensors that monitor a regularly used appliance and electricals. This technology could expand further to detect falls and provide help with managing medicines.

Carers UK has partnered with British Gas on the Hive project, alongside the charity Caring Communities, to enable those they support to stay in their own homes for longer.

Smart tech, it’s not all good news

As most homes are struggling to find a spare socket to plug in the latest bit of tech, sales of extension leads and triple adaptors must be going the through the roof. All these devices are only going to increase energy bills. Finding out what these bits of kit use isn’t easy. Nest, owned by Google, make lots of claims on how much you could save by using their thermostat. They then fail to publish meaningful data on their connected home products, such as their Google Home Hub and voice-activated speakers. We contacted them, through their chat service, over three months ago regarding this, and as yet, they have not updated any energy usage data information.

Amazon’s energy usage figures aren’t well publicised and are vague when compared to Apple’s. And we’ve yet to find any environmental reporting, by Amazon, regarding the materials, manufacturing or recycling – not great.

Apple, on the other hand, has got their environmental reporting act together – since the Greenpeace campaign against them a few years back. All the energy usage data is there in understandable terms. Materials used in its manufacture and recycling information are well publicised, unlike the other tech giants!

Other premium smart speaker brands such as B&O, Bose and Sonos appear to be ignoring the fact that their products consume energy. If data is provided it doesn’t reflect real-world usage.

As yet there are no reporting standards or energy labelling requirements for this new classification on products – tech and the market get ahead of the policy makers again! Hopefully, this will change as the market matures.

Could smart connected homes drive up your energy bills?

Whilst the energy usage of these devices may seem trivial, it’s the cumulative effect of tens of millions of these devices in our homes. All adding to the background energy usage across the country. Even small reductions in the energy usage of smart devices could make massive reductions in the overall UK energy consumption.

A more worrying aspect of these technologies – from an energy usage perspective – is the back-end cloud and network services driving these products. At moment there doesn’t appear to be much information regarding network/cloud and data transaction impact in carbon emissions terms. A host of other factors would need to be considered to get robust reporting on this, for example, data centres, server configurations, and how these are powered (renewables or fossil-fuelled) to give a view on their carbon impact.

Amazon cloud platform AWS, which hosts the software that drives Alexa, achieved 50% renewable energy usage in early 2018. Their in-house combined solar and wind generation is estimated at 2-gigawatt hours per year. This is used to power some of their server farms. However, if you took that energy generation away from powering the AWS servers and turned it to run Alexa home smart speakers, that 2 Gigawatts would only power approximately 95,000 units a year. It’s estimated that over 75,000,000 smart speaker units have been purchased worldwide in 2018.

Standby energy usage improves to be replaced by not so ‘smart’ stuff!

Back in the day standby and plasma TVs were seen as the villains of energy usage. Now most TVs (apart from supersized LEDs) and peripheral devices have cut their energy usage down dramatically. All good, however, standby is still a waste of energy.

Fast-forward to the present… we have a plethora of smart connected products filling up our homes, constantly drawing more and more background energy than standby devices ever did. And the hidden cloud services that provide the intelligence and computer processing power are consuming yet more energy as they monitor our lives!  So as fast as we make efficiencies, we find more ways to use electricity! The Jevons paradox.

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