First decide whether humidification is needed
PH04 combines functions absent from 250S; that does not establish better purification. Coway suits dedicated air filtration when humidification is unnecessary. We have not physically tested either device and have no joint test supporting an overall winner. Reviewed on 3 November 2026.
Two devices with different jobs
This page covers Dyson PH04 and Coway Airmega 250S, not the non-connected 250 or other Dyson models. PH04’s fan moves air; it is not an air conditioner. We withdraw estimated prices and promises to cool room temperature.
| Feature | Dyson Purifier Humidify+Cool Formaldehyde (PH04) | Coway Airmega 250S |
|---|---|---|
| Function | Purification, humidification and fan | Purification |
| App | MyDyson | IoCare+ |
| Documented filtration | HEPA, carbon and formaldehyde catalyst | Washable pre-filter and Max2 |
| Coverage | Not equated to the Coway figure | 465 ft² at 4 air changes/h, US listing |
| Water handling | Tank and maintenance | No humidification |
What each manufacturer states
Dyson documents purification, humidification, fan operation and MyDyson control, plus a formaldehyde catalyst. Coway specifies a washable pre-filter, Max2 and IoCare+. Its US listing distinguishes 465 ft² at four air changes per hour from 930 ft² at two. Quoting only the larger area hides that difference. No equivalent PH04 measurement is established here for an area comparison.
What HouseFresh found with 250S
Danny Ashton at HouseFresh in December 2025 says the unit was purchased and highlights high-speed cleaning performance. He reports a large noise jump between speeds one and two and reduced cleaning at the quiet setting. This limits the previous blanket recommendation for quiet bedroom use. His test does not establish an advantage over PH04.
What the humidifier evaluation adds
RTINGS assessed PH04 as a humidifier and praised cleaning access while noting size, humidification-efficiency and high-speed noise drawbacks. This assesses a different function and methodology, not purification against Coway. Dyson explains maintenance and the Deep Clean cycle: having that cycle does not remove the need to care for the tank and follow the model instructions.
What to check before buying
If you will not use humidification, consider its additional maintenance before paying for it. For both models check clearance, compatible filters and replacement costs. The Coway source used is a US listing: check voltage, warranty and distribution in your country before importing. We do not promise that a filter removes every odor or guarantees health outcomes. Shopping links are searches and require checking the reference, seller and package.