Why the Dyson Hot+Cool Formaldehyde air purifier won me over, despite its high price tag

Our Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater review puts the brand's 3-in-1 air purifier, heater, and fan through its paces to see how it compares to the best air purifiers, the best electric heaters, and the best fans the Ideal Home team has tested.

The Dyson Purifier Hot+Cool is fairly unique in offering this exact 3-in-1 functionality, with few other appliances delivering the same ability to control your indoor climate in as many different ways throughout the seasons. 

As an air purifier, the Dyson Purifier Hot+Cool also stands out from the crowd because of its stylish bladeless design, its HEPA H13 filter that Dyson states can capture 99.95% of particles as small as 0.1 microns, and its ability to remove formaldehyde from the air.

Formaldehyde is a chemical found in many new building materials and household products like laminated wood, MDF, fire-retardant fabrics, and glues. Most air purifiers don't manage to capture these super-tiny formaldehyde molecules that Dyson states are '500 times smaller than 0.1 microns'. The Dyson Purifier Hot+Cool uses a 'precise solid-state formaldehyde sensor with a unique catalytic filter' that the brand says 'breaks down formaldehyde molecules into water and CO2, and never needs replacing' to remove this additional potential pollutant from your home's air.

However, all of this comes at a price, with the Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater easily the most expensive air purifier, heater, and fan we've reviewed. As such, I was eager to put it to the test to see if its performance could justify its premium price tag.

Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater review

Specifications

• Recommended room size: 27m²
• CADR: not supplied
• Noise levels: 46-62dB
• Filter type: HEPA H13, formaldehyde catalytic filter, and activated carbon filter
• Dimensions: H76 x W22 x D22cm
• Weight: 5.5 kg
• Wattage: 6-40W
• Smart App connectivity: Yes
• Timer: Yes
• Auto mode: Yes
  

How I tested

Amy Lockwood

I'm Amy, one of the Ideal Home team's Ecommerce Editors. My job involves putting all manner of products through their paces to find the best recommendations for our readers. I tested the Dyson Purifier Hot+Cool Formaldehyde HP09 Purifying Fan Heater in my own home to see how it coped with everyday decreases in air quality caused by smoke, VOCs, cooking fumes, and dust.

Assembly and set up

The Dyson Purifier Hot+Cool Formaldehyde HP09 purifying fan heater arrives without its air filters installed, but unwrapping and inserting them into the body of the air purifier is a simple task. 

Unlike most air purifiers, the Dyson Purifier Hot+Cool comes equipped with two sets of filters. First, there's the blue 'selective catalytic oxidisation filter' which is the one Dyson states 'destroys formaldehyde'. This doesn't ever need replacing and simply needs to be slotted into the air purifier before its first use.

And then there's the HEPA 13 filter with activated carbon that will need replacing intermittently.

Both click easily into the body of the Dyson Purifier Hot+Cool and then the perforated bronze casing can be replaced.

The Dyson Purifier Hot+Cool is also Wi-Fi compatible so you can download and connect the purifier to the Dyson Link App for remote operation and in-depth air quality data, as well as connecting the air purifier to Amazon Alexa or Google Assistant for voice-activated operation.

Design

As you would expect from a Dyson product, it's immediately obvious from the Hot+Cool's build quality that this is a premium product, and its distinctive design sets it apart from the competition. 

This is no basic white cylinder as tends to be the case with most budget air purifiers, instead, the glossy lozenge-shaped bladeless fan, brushed metal base, and discrete circular LCD display scream considered design.

This is lucky, because this is a fairly large appliance, especially in height, measuring H76 x W22 x D22cm. And, because its 3-in-1 functionality equips it for year-round use, it's an appliance that's intended to be on display in your home most of the time.

Performance

As already mentioned, the Dyson Purifier Hot+Cool offers a lot of functionality. You can use this 3-in-1 appliance as an air purifier, a heater during the colder months, and a normal fan during the warmer half of the year.

However, I think it's unlikely you'd be spending this much money if you only wanted a heater or a fan, so it's the Dyson Purifier Hot+Cool's air purifying functionality that I spent the most time testing for this review.

Air Purifier performance

Turn the Dyson Purifier Hot+Cool on, and what's immediately apparent is the level of air quality data that you suddenly have at your fingertips.

The Hot+Cool features four sensors in all – a gas sensor that detects oxidising gases and VOCs, a temperature and humidity sensor, a particulate sensor that uses laser measurement to ascertain PM2.5 and PM10, and a solid-state formaldehyde sensor that uses an electrochemical cell to detect the presence of formaldehyde molecules in the air. 

All of this air quality data is then displayed on the circular LCD screen on the front of the Hot+Cool, including individual measurements of your home's overall AQI, temperature, humidity, PM2.5, PM10, NO2, pollen, VOC and HCHO levels. You can access more detailed reports (including helpful information pages on what all this data means) from within the Dyson Link App.

The App also allows you to download outdoor air quality information for your local area. This is especially useful if you live in a very congested or polluted area, as it helps you to gauge when it's preferable to open the windows to allow fresh air to circulate within your home, and when you may prefer to keep windows closed and use the air purifier to combat traffic pollution or high pollen levels.

Straight off the bat, this is far more accessible air quality data than any other air purifier I've tested, most of which simply rate air quality levels based on PM2.5. In comparison, the Dyson Purifier Hot+Cool breaks this data down into specifics, which could be super useful if you're trying to find an air purifier to help you combat specific pollutants or allergens. 

Armed with this information you can then either operate the Dyson Purifier Hot+Cool manually or use its automatic mode – which uses information gleaned from the sensors – to kick the Hot+Cool's air purification up a notch if air quality levels drop and switch the air purifier back to its lowest operational setting when air quality is good.

I was happy to see that when I first turned the Dyson Purifier Hot+Cool Formaldehyde HP09 on in my home it showed all green numbers on the LCD display with the sensors reporting an air quality measurement of 3μg/m3 PM2.5 (the lowest possible being zero).

To put the Dyson Purifier Hot+Cool Formaldehyde HP09 to the test, I switched it into automatic mode so that it was reliant on its sensors to control the air purification process, lit a match close to the air purifier, and let it burn out to create smoke in the air.

It took the Hot+Cool on average 40 seconds to register the smoke particles, at which point the air purifier kicked into action to clean the air. All in all, it took the Hot+Cool around 21 minutes to filter the air and return to an air quality measurement of 3μg/m3 PM2.5. This is a fairly long time compared to many air purifiers I've tested, but, when I left and then re-entered the room, my nose couldn't pick up any trace of smoke remaining.

I then tested the Hot+Cool's reaction time in filtering out VOCs from the air by spraying aerosol deodorant in the vicinity of the air purifier. Again, the Hot+Cool took around 40 seconds to register the drop in air quality, and this time around 4 minutes to return the air quality to its previous level.

Next up, I moved the air purifier into the kitchen for the bacon frying test to see how it coped with cooking fumes. 

My kitchen has a very old extractor fan that struggles to remove cooking fumes successfully, so I was interested to see how the Hot+Cool would perform in comparison. 

The Dyson Purifier Hot+Cool Formaldehyde HP09 is a lot taller than most other air purifiers we've tested, so whilst I wouldn't normally suggest you'd want it placed on a kitchen worktop, to make the test fair in comparison to the other air purifiers I've put through this process I positioned the Hot+Cool on my kitchen work surface a safe distance from the hob. I then shut the kitchen door, made sure the windows were closed, and left the extractor fan off whilst I started frying two rashers of plant-based bacon.

I timed from when the bacon first started sizzling, and it took the Dyson Purifier Hot+Cool Formaldehyde HP09 1 minute and 30 seconds to register the bacon smell and for the displayed PM2.5 levels to start to rise.

Around a minute later the bacon had finished crisping up, so I snuck out of the kitchen, shut the door again, and set to work eating my bacon sandwich whilst the Hot+Cool continued operating at high speed to remove the bacon fumes from the kitchen. 

I snapped a picture before I left the kitchen when the PM2.5 levels hit 220μg/m3, but all in all the Dyson registered PM2.5 levels of 799μg/m3 post-bacon frying before readings on the display began to drop.

All in all, it took the Hot+Cool 38 minutes to reduce the PM2.5 levels back down to a 'good' level of 12μg/m3 after the bacon frying. 

Considering the Dyson Purifier Hot+Cool Formaldehyde HP09's price point, I was a little surprised to find that in all three of these tests – particularly the smoke and bacon-frying tests – the Hot+Cool took longer to purify the air than many of the models I've put through the Ideal Home air purifier testing process. Most notably the super speedy Blueair Blue Max 3250i Air Purifier which is significantly more affordable and took just 11 minutes and 32 seconds to clear my kitchen of bacon fumes, and the powerful AEG AX91-604GY Connected Air Purifier which is designed to work in larger spaces than the Hot+Cool (up to 129m2) and cleared the air of cooking fumes in 11 minutes and 48 seconds.

This isn't to say that the Dyson Purifier Hot+Cool didn't work well at air purification, it did. And it offered far more comprehensive data on the levels of airborne particulates present in my home's air than any other air purifier I've tested. It just took a bit longer to remove particulate than I expected. 

But then, this isn't all the Dyson Purifier Hot+Cool does, so next up was putting its heater functionality through its paces.

Heater performance

Fortunately – or unfortunately, as it felt at the time – I had the opportunity to test out the Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater's heating powers when my central heating packed up whilst the outside temperature was just 3°C. 

Without central heating, the temperature in my house soon dipped to below 15°C and was continuing to fall by the minute. Thankfully the Dyson Purifier Hot+Cool is super easy to switch into heating mode. Just press a button on the remote and warm air will instantly start to gush from the upper lozenge-shaped section of the purifier. 

You can set your desired target temperature anywhere between 1°C and 37°C, and the Hot+Cool will then monitor the ambient temperature of your home and kick into action to warm things up should the temperature drop below your desired setting.

In practice, I was really impressed by the Hot+Cool's heating functionality. Its bladeless fan is very powerful and quickly pushes warm air out into the room to raise the room temperature fast, in fact, it didn't just warm the room but kept the entire top floor of the house warm whilst it was running. 

This powerful heating performance is helped by the Hot+Cool's 350 ̊ oscillation that ensures warmth reaches all four corners of your living space.

Fan performance

After being mightily impressed by the Purifier Hot+Cool's heating performance, it was pretty clear I was also going to be impressed by its fan performance. 

Whilst no fan can actively cool the air – you'll need one of the best portable air conditioners on the market for that – a fan works by circulating the air in the room which – when you're within reach of the air current – has the effect of cooling down the body. 

From my tests of its heating abilities, I already knew that the Dyson Purifier Hot+Cool was powerful at circulating the air within a space, and it certainly made a big difference in cooling me down when temperatures were high too. 

In fan mode, the Purifier Hot+Cool has 10 speed settings to choose from. Again, that 350 ̊ oscillation is great at bouncing air off all four walls to keep air moving within even larger space, and the bladeless design means that even though there is noise when the Hot+Cool is at its highest speed, it's only the sound of gushing air, with none of the mechanical whirring that tends to be part and parcel of operating cheaper bladed cooling fans.

Ease of use

The Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater can be operated either via the stylishly designed copper remote control or via the Dyson Link App.

There are no onboard controls, other than an on/off button to the front of the appliance, so you do need to pick up and put down that remote control carefully so as not to lose it. But, the remote control's curved design is magnetised so it stays in place on top of the air purifier when it's not in use.

The remote control buttons are laid out intuitively and easy to use, offering good functionality and a variety of ways to control the air purifier's operation. However, some users may find the understated symbols a little hard to read, and those with larger fingers may find the buttons set a little close together for comfortable use.

The App is also intuitively designed, and the fact that Wi-Fi connectivity offers the option of voice-activated control will be a big plus point for many users.

Noise levels

On paper, the 46-62dB rating of the Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater appears pretty high compared to many standalone air purifiers, heaters and fans. 

However, how intrusive any noise is depends as much on the type of noise as the volume, and in practice, I found the Dyson Purifier Hot+Cool didn't really disturb me when it was running, even at its highest speed. 

This is likely because, unlike most air purifiers which use fan blades to propel the air into and out of the appliance, the Dyson Purifier Hot+Cool instead utilises a bladeless design.

This means that there's none of the irritating mechanical whirring that can accompany cheaper bladed fans, and instead the noise emitted is entirely that of gushing air. 

For me at least, this was a type of white noise I found far easier to filter out. I'm a light sleeper, and I even managed to have the Dyson Purifier Hot+Cool running in my bedroom overnight without being disturbed.

Portability

Although the footprint of the Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater isn't that large, it is tall, measuring H76 x W22 x D22cm in all. 

It also weighs 5.5 kg, so although it is portable, it's not the most compact air purifier I've tested and does require a little more effort to move around the house.

Energy use

The Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater uses 6-40W of electricity depending on which mode you have it running in, which is on par with most air purifiers of this size. 

It also features intelligent sensors that allow for automatic operation, meaning it doesn't use more energy than is needed to maintain your indoor air quality and your preferred indoor climate.

You can find out more about how much it costs to run an air purifier in our dedicated guide and calculate the Dyson Purifier Hot+Cool's exact cost per use in line with current energy prices.

Filter replacement

Although the Purifier Hot+Cool's formaldehyde filter is designed to last 'a lifetime' according to Dyson, the HEPA 13 filter will need replacement. 

As of writing, replacement filters for the Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater cost £85. Although not as expensive as some, such as the AEG AX91-604GY Connected Air Purifier where replacement filters will set you back £100, this is more than the average replacement filter for a mid-sized air purifier, which is around £40.

Verdict

Unless you're lucky enough not to blink twice at investing nearly £700 in an air purifier, the Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater has a lot of work to do to justify its premium price tag. 

And I have to admit, after being thoroughly impressed by the performance of the much more affordable Blueair Blue Max 3250i Air Purifier, I wasn't sure what the Dyson Purifier Hot+Cool was going to be able to deliver to swing me in its favour. 

After all, the Blueair Blue Max 3250i is smaller yet can filter the air in a larger space (48m2 compared to Dyson's 27m²), it can remove 99.97% of airborne particles down to 0.1 micron in size as opposed to the Hot+Cool which removes 99.95%, offers the same Wi-Fi connectivity and option of voice-activated control, and is a quarter of the price of the Dyson Purifier Hot+Cool. The Blueair Blue Max 3250i also filtered particulate from the air far quicker than the Dyson Purifier Hot+Cool in my tests.

However, during testing, I discovered a lot I liked about the Dyson Purifier Hot+Cool. 

I was particularly impressed by the level of air quality data that's immediately available when you turn the Purifier Hot+Cool on. No other air purifier I've tested gives such a detailed analysis of your home's air quality, offering measurements of overall AQI, temperature, humidity, PM2.5, PM10, NO2, pollen, VOC and HCHO levels. If you suffer from allergies or are concerned about the presence of a particular pollutant in your home, this is excellent data to have at your fingertips.

And of course, then there's the 3-in-1 functionality. Initially, I wasn't sure how much use the multifunctional elements of the Dyson Purifier Hot+Cool would be in practice, but it only took one malfunction of my central heating for me to realise how valuable it is to have an alternative heat source easily to hand as back up. And the Purifier Hot+Cool's heating powers are fast and powerful.

As summer temperatures continue to rise, I'm also beginning to find a fan a necessity during the warmer months, and the joy of having a 3-in-1 appliance is that you don't need to factor in storage for three different appliances – particularly useful if your home is short on storage space. 

Overall, if you will use all three functionalities throughout the year, it becomes easier to justify the Dyson Purifier Hot+Cool's premium price tag. 

And, if you also take your home's air quality seriously and want the detailed analysis the Purifier Hot+Cool can provide, or you want an air purifier that can also remove formaldehyde from your home's air, the Dyson Purifier Hot+Cool Formaldehyde HP09 Fan Heater is in a class of its own.