Ductless ventilation filters air and sends it back into the room. A ducted system removes that air completely and pulls in fresh air instead.
That single difference decides what each one can achieve. It also limits ductless ventilation more than most marketing admits.
Ductless systems remove particulate and some odour through filters, then return the air. They cannot remove heat, moisture or carbon dioxide, because the air never leaves. Ducted systems remove everything, at the cost of installation work and conditioned air that must be replaced.
What each system removes
| Contaminant | Ducted | Ductless |
|---|---|---|
| Grease and particulate | Yes | Partly, through filters |
| Odour | Yes | Partly, through carbon |
| Heat | Yes | No |
| Moisture | Yes | No |
| Carbon dioxide | Yes | No |
| Combustion products | Yes | No |
Heat and steam are exactly what people want gone from a kitchen or a bathroom. So ductless versions of both tend to disappoint.
Where ductless genuinely works
- Flats where no outside wall or duct route exists at all.
- Light cooking, since there is little steam or grease to shift.
- Rented spaces, where nobody may cut a hole in anything.
- Lab filter cabinets built for one named substance.
- Workshops with a filter matched to one kind of dust.
- Finally, cold sites where heating the replacement air costs too much.
That last case matters in cold places, where every cubic metre you throw out has to be heated on the way back in.
Filter limitations
Ductless ventilation is only as good as its filters, and filters fill up.
Grease filters need cleaning often. Carbon filters saturate and then stop working altogether. Meanwhile a full carbon filter gives no warning at all, so the unit keeps running while removing nothing.
Most ductless installations disappoint because nobody replaces the carbon. Set a replacement schedule at handover rather than waiting for complaints.
The energy comparison is not obvious
A ducted system throws away conditioned air, and something has to warm the replacement.
- Throw out 500 m³/h in winter and you must heat 500 m³/h of cold air.
- That can cost several times what the fan itself uses.
- A heat recovery unit wins most of it back, for a higher price.
- Ductless ventilation avoids the loss completely.
- However, it also fails to shift heat, steam or carbon dioxide.
- Finally, demand control cuts the loss on a ducted system a long way.
So the honest answer depends on the climate and on what really needs to go.
Installation and cost
Ductless ventilation costs less and installs faster, which is its main commercial appeal.
There is no hole through the wall, no duct route through the building and no roof terminal. Meanwhile a ducted system needs all three, plus a make-up air plan on anything sizeable.
Our duct fan comparison covers the ducted options, and our commercial kitchen guide covers the make-up air side.
Choosing between them
Two questions settle the ductless ventilation decision quickly.
First, does anything need removing that a filter cannot catch? Heat, steam and carbon dioxide all say yes. Second, can a duct route be built at sensible cost? Where both answers agree, the choice makes itself.
For ventilation rates, ASHRAE Standard 62 sets out the accepted figures, and most codes point at it.
One last thought for anybody weighing the two. Heat recovery has changed this argument in the last decade. A good recovery unit removes contaminants properly and gives back most of the heat, which removes the main reason people reached for ductless ventilation in the first place.
Ventilation type FAQ
Is a ductless cooker hood any good?
For light cooking it manages grease and some odour. It cannot remove steam or heat, so a kitchen with a ductless hood still gets hot and humid.
Can ductless ventilation satisfy building regulations?
Often not, since most codes want air removed rather than recirculated in kitchens and bathrooms. So check the local requirement before you specify anything, because retrofitting a duct route afterwards is expensive and disruptive.
How often do carbon filters need replacing?
Typically every three to six months with regular use. They saturate silently, so a schedule matters more than inspection.
Does heat recovery change the comparison?
Considerably. A heat recovery unit removes contaminants exactly as a ducted system does, while winning back most of the heat. That answers the main argument people make for going ductless in the first place.
Ductless ventilation filters what it can catch and returns everything else. So where heat, moisture or carbon dioxide matter at all, only a ducted system will actually do the job.
