- Why does 150mm ducting matter?
Because your extractor can only perform as well as the air path allows.
This is something Miro absolutely hammer home to our retailers, customers, fitters and end-users.
A smaller duct creates greater resistance.
Then add:
- bends
- long runs
- flexible ducting
- reductions
- poor transitions
…and the resistance increases further.
The result can be:
less airflow + more noise + poorer extraction.
Miro recommends (and insists upon) 150mm / 6″ rigid round ducting wherever possible, or 220 × 90mm rigid rectangular ducting, with short and direct routes preferred.
What do we advise?
Don’t spend thousands on your kitchen, add a stylish extractor and then strangle it with £20 worth of inadequate ducting.
- How long can an extractor duct run be?
There isn’t one universal answer.
The maximum acceptable duct run depends on the extractor, motor, duct diameter, number/type of bends and installation configuration.
A short, straight 150mm rigid duct is dramatically easier for a motor to work against than a long, convoluted route with multiple elbows.
Think of it like this:
Best
Extractor → short straight duct → outside.
Acceptable
Extractor → moderate rigid duct → a couple of bends → outside.
Problematic
Extractor → long run → multiple bends → reductions → flexible duct → outside.
The important thing is to consider ducting before the kitchen is ordered, not after.
For a particular Miro model, the installation manual and manufacturer guidelines should take precedence over generic advice.
- How many bends can I have?
Simply, as few as possible.
There isn’t a universal “you can have exactly four bends” rule – every bend introduces additional resistance.
And not all bends are equal.
A smooth, properly formed elbow is preferable to a badly crushed or abrupt change in direction.
Miro specifically recommends minimising elbows and avoiding diameter reductions around elbows.
So rather than asking:
“How many bends can I have?” ask “How can I design the duct route with the fewest restrictions?”
- Why can flexible ducting reduce performance?
Because flexible ducting can become a complete mess, if not used properly.
When properly installed, it has its uses.
But if it becomes:
- concertinaed
- crushed
- sagging
- twisted
- “mushroomed”
- full of unnecessary bends
you’re effectively putting obstacles in the airflow.
Miro has seen this first-hand through service issues: problems that appear to be an extractor fault can actually be caused by the ducting. Putting it in its simplest form – rigid ducting = smother airflow.
- External wall vents explained
The final part of the journey matters too.
You can have a fantastic extractor, powerful motor and correctly sized duct – but if the external vent is poorly designed, you’ve still got a restriction.
The external vent needs to:
- allow air to discharge effectively
- avoid unnecessary restriction
- be appropriate for the duct size
- protect against weather ingress
- be correctly installed/sealed
- comply with relevant building requirements
Don’t reduce a 150mm system to a tiny outlet simply because the external grille looks nicer.
The air doesn’t care how pretty the grille is.
- What happens when an extractor is undersized?
It struggles! You may notice:
- lingering smells
- steam travelling around the kitchen
- grease settling on surfaces
- condensation
- poor capture around the edges of the hob
- the extractor running constantly
- increased noise
- disappointment with an otherwise perfectly good appliance
And there’s another trap:
A larger extractor isn’t necessarily the solution.
If the ducting is restrictive, increasing motor power can simply mean you’re asking a bigger motor to fight the same bottleneck. That’s why at Miro we talk about the complete extraction system, not just motor power.