Dyson HP04 Pure hot+cool purifier/fan/heater

portable home heating

The new Dyson HP04 Pure Hot+Cool purifier/fan/heater is another addition to the Dyson stable improving on its highly successful, and highly intelligent, Pure Cool released last year.

The Dyson HP04 Pure Hot+Cool purifier/fan/heater is three devices wrapped into one. Its claim to fame is the purification mechanism that not only traps 99.95% allergens like dust and pollen but volatile organic compounds (VOC), petrol/diesel fumes (NO2) and those that emanate from flatpack furniture and cleaning products.

We put the Dyson HP04 Pure Hot+Cool purifier/fan/heater through its paces and see how it justifies the premium $899 price tag – not to mention the $100 each year or so to replace the filters. Dyson is, as always, an investment in a premium product, and it sells heaps.

First – as Dyson would love – the 101 Dummies Guide to Air movement and purification

A typical fan pulls air from behind it into the blades and expels it at the velocity (speed setting) you select. It is a one-way airflow, e.g. X litres of air-per-minute in and then the same X litres out.

Dyson uses an ‘air multiplier’ effect that can increase the output (not input) efficiency by up to 10 times.

Dyson HP04 Pure hot+cool air multiplier

Dyson scientists and engineers have very effectively harnessed the Coandă effect named after  Romanian aerodynamics pioneer Henri Coanda. Simply put Dyson ‘bladeless’ fans blow the air out over a curved surface, and it takes the surrounding lower pressure air with it increasing air output. For example one litre sucked in can pick up to nine extra litres of surrounding air to push out.


Air intake versus Air output or Clean Air Delivery Rate (CADR)

Dyson HP04 Pure hot+cool advertise 290 litres/second airflow. We know that is the air output, including the Coanda effect (Air Multiplier) at a maximum fan speed of 10. We can safely assume on fan speeds of 1-5 the efficiency is 1-5X etc.

What Dyson do not state is the actual air intake – volume sucked into the purifier in cubic feet or metres per minute – or CADR. This is useful to compare it with other purifiers that state CADR and helps to select the right size purifier for the room size.

Our guesstimate was about 29 litres-per-second (lps) using Dyson’s stated 10X multiplier effect. But the previous model (similar design specs) states a CADR of 60 cubic feet per minute or 1.688 cubic metres per minute. And guess what – that is 28.32lps or in CADR terms about 100m3 per hour!

More science

A cubic metre (1x1x1m) contains 1000 litres of air. So, if you have a small bedroom room 3 x 3 x 2.4m that is 21.6m3 or 21,600 litres of air. A larger room – say a lounge 5 x 5 x 2.4m is 60m3 or 60,000 litres of air.

Now many Aussie home have high or vaulted ceilings and large open space living areas. These have no confined area, so purification, heating or cooling is far more problematic as air can flow in from elsewhere including open windows, doors etc.

If you place the Dyson in that small confined bedroom (21,600 litres@29lps) air would turn over every 12.5 minutes. But you will not run the fan on 10 because it is a little noisy in a small space so using linear assumptions:

  • Fan speed five = 25 minutes to turn over the air (approx. two times an hour)
  • Fan speed one (night mode is 1-4) = 125 minutes or less – (approx. once every two hours)

How many times do you need to turn over the air to purify it?

Air Change Rate (ACR) does not specifically relate to purification but to air coming in from outside to inside keep the home well oxygenated. That air can contain pollutants like pollen and noxious gasses.

Dyson’s role is to help purify the air once it is inside the ‘designated area’ and also to remove impurities emanating from inside – cooking fumes, furniture polish etc.

Recommended ACR for a bedroom (21.6m3) is 5-6 times an hour and a lounge (60m3) is 6-8 times per hour.

The Dyson at 100m3 CADR (maximum) will evenly purify and heat the bedroom quite well even if the fan were set too much lower speeds overnight.

But as home spaces grow larger or more open-plan, Dyson relies on creating a micro-climate zone and just purifying or heating that rather than the whole area.

The definition of the micro-climate zone relates to the ambient temperature and humidity outside the zone and inside it. We use a Kestrel Drop temperature and humidity sensor to find the perimeter of the zone.

But wait there is more

We are not knocking Dyson but educating readers that there is a difference between CADR rating and Dyson airflow. Dyson is one of the few devices that can create a micro-climate zone (using the Coanda effect) within an overall larger space and in our book that makes it far more energy effective than a larger fan or heater or using reverse-cycle AC.

I like that you can adjust the air oscillation direction to create a defined zone from 0-350° or user-definable in between. It has up to a 40° tilt.

And for those that do not want any perceptible airflow, it has a diffused mode that turns the air backwards for gentle purification.

Dyson HP04 difused

Dyson HP04 Pure Hot+Cool purifier fan heater

Website here

User videos and FAQs here  

What is it?

Dyson HP04 Pure hot+cool remote

An all-in-one

  • Purifier (uses replaceable both HEPA and activated carbon filters)
  • Fan for air circulation (we refuse to call this ‘cooling’)
  • Heater
  • Remote control
  • An LCD and app for real-time feedback and contro
  • And an innovative no-blade design that is safe around kids and pets


  • Download the Dyson app for Android (tested) or iOS
  • Pair the Dyson with the app and your home Wi-Fi
  • Register for a 2-year warranty

You do not need the app, but it can be handy for remote access and to see weather and air conditions. Note: Dyson does not sell the information, so there is less need to be paranoid.

Last model – 2017-18 review

We reviewed that here in February 2018 – it scored 4.4-out-of-5. To be fair to Dyson, it was not long after I started at GadgetGuy. I did not have the reviewing expertise or test tools that I have today. Never-the-less it was accurate. Our only issue then was the apparent eye-watering price, not only of it but all Dyson products.

Well, time has passed, and as I get wiser, I appreciate the Dyson formula.

  • Leading-edge science in airflow
  • Leading-edge science in its fan motor
  • Absolutely no design compromise – properly or not at all as evidenced by the number of prototypes and scientists involved
  • And ironically Dyson’s next model always improves on its last

And we do not comment on price as that depends on what the market is prepared to pay. It appears that there is a market segment that drives Rollers and wants Dyson. Don’t we all ascribe to that?

Let’s examine the Dyson HP04 Pure Hot+Cool purifier/fan/heater

It is a 3-in-1 machine.


It is not this review’s purpose to justify air purification. There can be health benefits in removing air born dust, particles and gasses. If this is your primary need, then there are many brands of dedicated purifiers (some with humidifiers) that may meet your needs at a lower cost than a 3-in-1 device like the Dyson.

Dyson HP04 Pure hot+cool LED

The Dyson HEPA filter removes 99.95% of allergens and pollutants down to .1 microns (that is almost perfect). Its activated carbon filter also removes gasses like formaldehyde, benzene and NO2. These figures meet or exceed asthma or hay fever recommendations.

Dyson HP04 Pure hot+cool Filters

If you buy the Dyson, you must accept that it will need regular replacement of the 360° borosilicate glass microfiber HEPA (High-Efficiency Particulate Air) filter at $55 and the inner activated carbon filter at $55 when the machine/app tells you. Dyson suggests every 12 months based on 12 hours a day (4300 hours). I suspect that the average Aussie will probably get far longer out of it unless you leave it on the purifier only setting that is always on.

As a fan

This is a trade-off – the safety of no blades and the Coanda effect or an outright gale.

Several, less erudite bloggers have complained that they cannot feel the ‘wind in their face’ from a Dyson – poor, illiterate souls. Dyson creates a micro-climate in a defined zone bathing you in pleasant, clean, heated or room temperature air.

Contrary to advertising, no fan cools. It blows air on your body and in doing so helps to evaporate sweat making you feel a little cooler.

As Dyson is not ‘blowy’, it does not feel cooler – perhaps a degree or so. But it is very efficient at air circulation in the micro-climate and will circulate air more efficiently so that ground level cooler air replaces hotter air (which rises).

If you want true cooling, get an air-conditioner and a wealthy benefactor to pay for it.

As a heater

We ran two tests using our EmberIQ metre we can measure energy use in kilowatts per hour and cost.

  1.  Large open space lounge/media/kitchen/dining area of about 200m3. 12° outside and 17° inside and target zone temperature 20-22°

Depending on fan speed, temperature setting and oscillation, it can raise temperatures inside a micro-zone of approx. 4 x 5 x 2.4m ceiling (50m2) to 20-22° – a 3-5° increase. The temperature is warmest in a cone shape from the unit and drops off around the edges.

Heating energy use varies from 2000-2500W, and the test averaged 2000W. Peak electricity costs about 50 cents per hour (from 7 AM to 10 PM), so it is about $1.00 per hour. Off-peak and shoulder running costs would be 25-50 cents per hour.

open space
  • Enclosed bedroom approx. 4 x 5 x 2.4m ceiling (50m2) to 19° on Night mode

This is great to keep the bedroom at the ideal sleeping temperature after it reaches the target temperature. Interestingly the wattage initially only drops to 1900W until it reaches the desired temperature. Then it plummets to 3W until it needs to fire up again. The spikes below between 00:00 and 09:00 show it cycling up and down before the bigger spike at around 07:30 when it needs to work harder to keep the bedroom at 19° after we opened the main and bathroom doors. Energy use overnight on off-peak rates is negligible and ensures a constant temperature in a closed room.

closed room

Heater observations

It is easy and quick to get a micro-climate zone to the desired temperature 20-22° – 20 minutes at worst.

But to get above that, you set a target temperature (up to 37° and fan 10 – pity those poor Poms who need this) and it can take quite a. As a test we set it to 37°/10, and after 10 minutes the air temperature at the fan was 47°, but one metre in front was 28°. A further 10 minutes saw it rise to 29°.

If your need is ‘hot’ or to cover larger spaces, then you need to look at fan-assisted space heaters or reverse cycle air-conditioning.


At worst its 40-60dB (+/-10%) at 30cm (fan speeds 1-10) which equates to 35-45dB at two metres. It produces a gentler whoosh instead of a typical fan noise.

GadgetGuy’s take – Dyson HP04 Pure hot+cool purifier/fan/heater

There is no doubt that, as with all Dyson products, there is a truckload of science behind it. I tried to explain some of that because otherwise, all you would see is the price.

  • It is a three-in-one unit and the main compromise over dedicated units is the maximum purifying/heating space which we believe is about 25-35m2 or 60-80m3
  • CADR is approx. 100m3 – do not expect it to be as efficient in open space
  • As a sealed purifier it is more efficient than most
  • The build quality is a ‘keeper’
  • Dyson support and spare parts are legendary
  • There are more electronics (smarts) in this than any other similar device

As this is a three-in-one device, and we rate it with convenience at the forefront.

You can buy separate fans, heaters and purifiers (like the Philips range) that may have more capacity.

There are very few combos that can match the Dyson. If you want to spend less and sacrifice some purification, we recommend the De’Longhi HFX85W20C (review here).

Value for money
Ease of Use
You can simply plug and play or use the app for extra functionality
Dyson quality - its a keeper
Elegant, safe bladeless design
App for remote control and climate stats
Perfect for apartments and smaller areas
Not for larger open space designs unless you are happy with a micro-climate