Should I leave an air purifier on the whole day

Should I Leave My Air Purifier On All The Time?

can i use an air purifier all day

Having clean air in your house all the time is very important and one of the best ways to do this is by using an air purifier. However, you need to know how best to use your air purifier to ensure you get as much clean air in your home as possible and part of achieving all this is understanding when and how long to use your air purifier. This brings us to the main question of this post.

Can you leave your air purifier on all day? Most air purifiers are designed to operate 24 hours a day just as a fridge does. However, there are some exceptions. Some air purifiers such as ozone generators can only be used when no one is around, while devices such as some desk and car air purifiers are designed for use only when the user is around.

Given, the way air purifiers work it only makes sense to leave your purifier on all day. Because the air in your house is constantly changing as you move around bringing stuff in and out, your air purifier needs to be on all the time to deal with all the various pollutants that get introduced to your indoor air throughout the day.

Furthermore, every time you turn off your air purifier it does not take long before your air quality drops to the same level as it was before it was cleaned. This means your air purifier has to pretty much start from scratch cleaning your air and depending on your room size and type of device, it can take anywhere from 30 minutes to 3 hours for your air purifier to completely clean the air in your room again. So if you ask me, I would rather keep my purifier on the whole day to ensure the air in my home is always clean.

In my reflections about using an air purifier 24/7, some of the scary thoughts that crossed my mind were whether it could overheat and catch fire while I'm not around or whether it puts my health at risk in any away if I run it all night next to my bed while I sleep. I also found myself wondering which types of purifiers are best for 24-hour use.

Besides my worries, I found other people were also concerned about how much energy an air purifier will use and the costs involved in running one 24/7. As I tried to find answers about leaving a purifier on 24/7, I also found some people wondering about the conditions under which you can run one all day. If any of these concerns crossed your mind too, you will be glad to hear that I answer all these questions in the rest of this post starting with what kind of air purifiers are best to run all day.

What are the best types of air purifiers for all day use?

Based on what I have found throughout my time learning about air purifiers, the best type of purifiers to run all day do not produce any by-products and require the easiest and the least maintenance. The purifiers I found that best meet this criterion, are photocatalytic oxidation (PCO) and HEPA air purifiers.

HEPA air purifiers work by sucking air through a filter which traps contaminant particles in the air that are as small as 0.1 microns. Pollutants that HEPA filter air purifiers can trap include all kinds of dust, pollen, and pet dander. Good HEPA filters also come with activated carbon filters which enable them to get rid of odors by absorbing odor-causing air particles and gases.

HEPA filter purifiers do not release any by-products and are commonly used in places such as hospitals which require clean air 24 hours a day. Like hospital HEPA air purifiers, a typical household HEPA purifier is designed for 24-hour use and will do just fine in keeping your air clean if you don’t have serious indoor pollution problems.

However, if you have problems like mold, airborne bacteria, and viruses or volatile organic compounds (VOCs) then HEPA purifiers will not really help you no matter how long you run them. Also, a critical limitation with HEPA air purifiers is that they stop cleaning air efficiently in spaces larger than 1000 sq ft and you will need multiple devices for such situations.

This is where PCO air purifiers come in. PCO air Purifiers work by using wide spectrum ultraviolet light that's focused on a thin film of titanium dioxide which acts as a catalyst in an oxidation reaction that destroys pretty much all air contaminants that pass through the purifier. These two components sit in a reactor chamber inside the purifier which has fans that draw air in and out of the device and through the reactor chamber.

PCO purifiers are also designed for 24-hour use and clean air very well in large spaces of up to 3500 sq ft before additional devices are needed. Unlike HEPA air purifiers, they don’t just trap contaminants. They literally burn and destroy them and this includes odor-causing particles.

PCO purifiers can deal with air contaminants that are small as 0.001 microns and this is pretty much all the contaminants you need to get rid of in your house. These devices are also nice to run 24 hours because they operate very silently (almost noiseless) compared to other types of devices.

That said, with such good functionality comes a high price tag. A good PCO air purifier will cost you upwards of US$600. If you are going to get an air purifier that cost more than US$600, I personally would just go for PCO purifier. My preference would also be a PCO device in cases where I am dealing with more than just dust and pollen and there are smaller pollutant particles involved.

Beyond the ability for these technologies to clean air effectively while staying on all day long, whatever air purifier you get, you need to make sure it has automated functionality. This will save you on time and costs.  

At a minimum, go for devices that can automatically adjust their air cleaning speed based on how dirty the air in your house is. You also want a device with a timer and the ability to turn itself on and off. Even better, there are now purifiers on the market that you can link to your WiFi and control from your phone or laptop.

What type of air purifiers are not good for 24-hour use?

Now that you know which purifiers are best for 24 hours operation, I think it’s also important to know which ones to avoid.  I can tell you this immediately, “Do not waste your time and money or even think about ionic air purifiers and ozone generators if you are looking for an air purifier you can leave on all the time.

The problem with both of these devices is that they produce ozone as a by-product of their purification process. When inhaled long enough, ozone can irritate your lungs, cause shortness of breath, headaches and all sorts of breathing problems especially if you have a preexisting respiratory condition like asthma or bronchitis. So you can just imagine the dangers of running ionic purifiers or ozone generators all day in your home.

Furthermore, on top of producing ozone, most ionic air purifiers also leave a thin film of dust on surfaces around your house. This gives you extra cleaning work and the thin film of dust contains contaminants that could be reintroduced into the air if you do not clean up the mess properly. In my opinion, you definitely do not want this kind of device operating 24 hours in your home.

The story is a bit different for with ozone generators. As much as you should not be running them all day long, they actually serve an in important role in cleaning the air. The ozone they produce is dangerous but only because of its strong antibacterial and cleaning properties.

Ozone is very effective at killing mold, odors, bacteria, and viruses in the air. However, ozone generators should only be used when there is no one in your house for the day and turned off at least an hour before anyone gets back home.

The best situation to use an ozone generator is on spring cleaning day. Ozone generators are usually used by professional home cleaning service providers and I personally think that unless you are a highly technical person, you should keep away from them.

Besides ozone air purifiers, other purifiers you should avoid are some the are specifically designed for your desk or car. These are usually classified as personal air purifiers. Even if you are able to run these devices for 24 hours without any hustles, they could barely make a difference in the air quality of your whole room as they are too small and designed for your personal space.

In summary, if you did not understand anything else from this section, understand this,

“Stay away from ionic and ozone-based air purifiers if you want an air purifier that you can run all day.”

If you must get an ionic air purifier for whatever reason, get it as a combo with a HEPA or PCO air purifier with the option to switch the ionic part on and off.

Is leaving your air purifier on all day or while you sleep dangerous?

I already mentioned the dangers of ozone producing air purifiers. However, even with HEPA and PCO air purifiers, like any other electronic device, air purifiers can fail. I have seen cases of air purifiers bowing up but it is not a common occurrence.

The best advice I can give you here is to follow the instructions in your manual. But the general rules safety rules that apply for other electronic devices apply for air purifiers. Do not put your air purifier next to wet areas of your home, to avoid short-circuiting your device with water. You also need to keep your air purifier out of the way of pets and children.

In view of this, leaving your HEPA and PCO air purifiers on all day is as safe as leaving your microwave, fridge, TV or aircon on the whole day. Furthermore, if you are running either a HEPA or PCO air purifier in your room while you sleep, rest assured it will not be bad for your health. More than anything you should sleep more comfortably from a breathing perspective.

There is really no danger in keeping an air purifier on the whole day if you are using the right type of air purifier.

What are the costs of leaving your air purifier all day?

Both PCO and HEPA purifiers come with their various running costs but the main costs you have to consider are energy costs and parts replacement costs. From an energy consumption point of view, Most HEPA and PCO air purifiers are rated between 60 watts and 300 watts. So they consume less energy than a laptop, fridge or TV would consume if left on the whole day.

PCO purifiers are known for their energy efficiency as they consume as little electricity as a light bulb. Generally speaking, if you left an air purifier on the whole day for a year, depending on your type of device according to Consumer Reports it would cost you anywhere between US$30-US$200  per year in energy. You can work this out for yourself using the following formula:

“Watts  x  US$/KwH  x  Hours of Operation”

You will find the watts on your devices box or specs online, the KwH is just how much you get charged per Kilowatt hour of electricity where you live and for hours of operation you can just say 24 hours and multiply this by 365 to work it out for a year.

So that's energy costs for you. As for replacement parts, HEPA purifier filters can cost you up to $200 from as little as $20  depending on your device. For PCO purifiers you have to replace the reaction chambers and this will cost you around US$150. The deciding factor, in my opinion, is how often you have to replace parts.

HEPA filters have a much shorter lifespan than PCO reaction chambers at 3 months to  2 years while reaction chambers last anywhere from 1-3 years. It might work out cheaper to own a HEPA filter despite more frequent part replacement but from a maintenance perspective PCO air purifiers, a very low maintenance and will take very little of your time compared to HEPA filters.

Putting the 2 costs together, I think with a decent device it should not cost you over US$100 per device in terms of electricity consumption and if you replace parts every year, you should be able to operate your device easily at under US$250 per year including electricity costs. These are the major cost dynamics of running your air purifier all day and all year round.

Under What Conditions Can Use Your Air Purifier the Whole Day?

If you have read this whole post and gotten this far, by now you should be confident that you can leave your air purifier on the whole day. Be that as it may, there a few minor things you should be aware of and you should do to get the most out of your air purifier when running it all day long.

Firstly, you need to know the size of your room to determine what size air purifier you need to effectively clean the air in your room or around your house. If the area you want to cover is too large or you have multiple rooms your device could prove useless no matter how long you run it.

My rule of thumb is to get a device that is able to cover at least 300 sq ft  (square feet) more than your room size or space you want to cover. So if you have an area of 1000 sq ft get a device that covers at least 1300 sq ft.

Next, you need to keep windows and doors closed all the time to minimize the number of new pollutants coming into your home and the work load on your air purifier. Look, you can open windows to air out the house if you burnt something while cooking or someone dropped a human gas bomb but as soon as the air has cleared, close your windows. This will prevent pollutants from outside your home continuously entering your home and ensure that your air purifier maintains the best possible air quality in your home.

Your purifier will continue to run when your windows are open.  However, the more your purifier works the quicker it's filtration or cleaning technology wears out because of all the extra outdoor pollutants it has to clean. So to avoid unnecessarily overworking your device, and keep the air quality in your home at optimal levels keep your home enclosed from the outdoors as much possible if you have your air purifier running full time.

Lastly, it is very important to keep your house clean and free of clutter and to stop pollution in your home at the source even when your air purifier is operating 24/7. If you have carpets, drapes or chairs that easily absorb dust and odors, vacuum them with a good HEPA vacuum.

Ensure your basement is waterproofed and leakages are fixed to avoid eventual pollution from mold or mildew. Use safe cleaning chemicals that don’t off-gas but also leave your house smelling fresh. There is just so much you can do for me to cover here from a cleaning perspective to reduce pollution in your home. If you want to learn more about how to clean your house for fresh air you can check out my comprehensive post about that here,

So, in short, the main conditions you have to pay attention to if you want to optimally leave your air purifier on all the time include the size of the area where you need clean air, keeping the areas where your purifier is placed enclosed (i.e your air purifiers position) and finally keeping your house clean.

For more information on which exact air purifiers you can get that can run all day and all year long, check out my post on recommended room air purifiers here. All the recommended devices I show you unless I specify otherwise can be left to run the whole day and come with smart features that optimize their performance as they do so.

About the Author


Jean is a research economist by profession and he runs Fresh Air Genie. He is enthusiastic about maintaining good air quality at home and on the go and he shares his knowledge about this here at Fresh Air Genie.

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