Should I leave the AC running at night? 3 reasons sleep experts say you shouldn't if you want a really good night's rest

There are a lot of things to love about summer, but sweaty and uncomfortable sleep isn't one of them. There's nothing worse than thrashing around in a tangle of sheets - one leg in, one leg out - as you try to cool down enough to get your all-important shut-eye. If you're lucky enough to have it, switching on the air conditioning can offer some sweet release, but should you really be leaving your AC on all night? 

Without a doubt, aircon units are the best way to cool a room down quickly. When high temperatures and humid conditions make sleeping a struggle, the continuous waft of cool air and the gentle hum of the machine really can feel like the ultimate luxury. But, while it might help you sleep better at first, experts warn that leaving the AC on overnight may not be the best idea in the long term.

From increased energy costs to potential health risks, there are a host of reasons why you might not want to run your aircon through the night, and they outweigh the benefits of that initial blissful breeze. We spoke with some sleep and appliance experts to find out more, and their reasoning might change your relationship with your AC for good. 

Is it bad to leave AC on all night?

When it comes to how to cool down a room, AC is the obvious choice. But, as tempting as it might be to leave your aircon on to stay cool through the night, experts say it might not be doing you any favors. 

First off, there are several health implications to consider. 'When you sleep at night, your body’s internal temperature drops, which helps promote better sleep,' explains Christine Kingsley, Health and Wellness Director of the Lung Institute. 'However, if the temperature of your AC drops the room temperature lower, your immune system will slow down, making you more susceptible to conditions, such as a common cold or a dry cough.' 

You're also more likely to wake up dehydrated if you sleep with the AC on in your bedroom, too. 'This is because AC can also dehumidify the air as part of its cooling process,' notes Christine. 'This can lead to a dry throat, mouth, lungs, and eyes, which can eventually lead to an irritated respiratory system.' 

As well as these adverse effects, air conditioners are hungry energy consumers. If you're conscious about cutting your energy costs and doing your bit for the planet, you ought to turn the AC off before you sleep. 'ACs consume a large amount of energy, which can add up over time if left on all day,' explains Matt Kerr, a Machine Learning Engineer and the founder of Applianced Geeked. 

That being said, Matt's keen to note that leaving AC on continuously could actually be more economical than turning it on in intervals. 'Leaving the air conditioner on overnight helps it to cool down without working overtime, resulting in decreased energy expenditures,' he says. With this in mind, it's a good idea to run the AC continuously for a few hours in the evening before going to sleep. 

What are the benefits of turning your AC off at night? 

There are a host of advantages that come with turning off your AC at night, and while switching it on might be a core part of your bedtime ritual, knowing these insights could change your habits once and for all. 

1. Turning of AC overnight is better for your health

We already touched upon the health impacts that result from sleeping with the AC on, and while it might sound counterintuitive - especially since cooler environments are said to be better for sleep - a stuffy bedroom is actually preferable to one that's air-conditioned throughout the night. 

'Due to low moisture levels and a lack of fresh, filtered air, AC might produce sluggishness, lethargicness, and headaches,' says Matt. 'Acclimatization to cold air can also have negative consequences on the body, making it harder for the internal thermostat to adjust to warmer conditions, generating internal and external tension, and eventually lowering general well-being.' 

You're also less likely to become ill if you turn the AC off while you sleep. Not only can the colder temperatures affect your immune system, but aircon machines can circulate infectious air. It's especially important to avoid if you suffer from allergies too, since unlike air purifiers, AC doesn't clean your air. As Christine explains: 'An AC will circulate the air inside your room, but it will also circulate any allergens that are present in the air – dust, mites, spores, and pollen. Without an AC, you can prevent subsequent respiratory conditions, such as runny nose, itchy throat, sneezing, and even breathing difficulties.'

2. You'll save energy (and money)

We're all looking for ways to save energy, and turning your AC off overnight is a good place to start. 'If you turn your air conditioner off at night, you can save energy and money,' says Isabella Gordan, sleep expert and CEO of Sleep Society. 'It also helps to reduce your carbon footprint since there is less strain on the power grid and fewer emissions released into the atmosphere.' 

Turning off your aircon appliance will also reduce strain on the machine and improves overall efficiency. 'Furthermore, continuous operation might cause the air to get overly cold, which could harm the evaporator or coiling coil component,' says Matt. 

3. Turning off aircon can help you sleep better 

In general, a slightly cooler environment is best for helping you sleep, but continuous AC can actually make a room too cold, causing disruptions to your sleep pattern. As Christine points out: 'By turning off the air-conditioning you can avoid sleep disturbance caused by shallow temperatures. Sleeping in an environment that’s too cold for your body can negatively impact your sleep quality as the cold can wake you up shivering.' Older AC machines can also be quite noisy, which can also contribute to disrupted sleep. 

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