Invisible / Plaster-In Air Valves – What Is Actually Needed?
Invisible air valves (or plaster-in valves as most people call them) have become really popular over the last few years — especially on higher-end residential jobs.
We’re getting asked about them more and more, particularly the Ergovent Rondo and Ergovent Kvadro diffusers, which seem to be the go-to choice for that clean, modern finish.
They look great when they’re done right.
But the key thing we see time and time again is people treating them like a standalone product — when in reality, they’re just one part of a full duct system.
What Actually Is a Plaster-In Valve?
In simple terms, it’s just a vent terminal that gets plastered into the ceiling or wall so it disappears visually.
Once it’s finished, you’re left with a neat slot or opening instead of a plastic grille — which is why they’re so popular in:
- New builds
- Architect-led projects
- Open-plan spaces
- Anywhere appearance really matters
They’re designed to blend in, not stand out.
The Big Misunderstanding (We See This a Lot)
This is the important bit.
The valve itself does not move air.
It’s not a fan. It’s not doing any “work” as such — it’s just the end point of the system.
We’ve had a few enquiries where people thought installing one of these would solve ventilation on its own… it won’t.
Without a full setup behind it, it’s basically just a hole in the ceiling.
So What Do You Actually Need?
To get one of these working properly, you need to think of the full airflow route — not just the visible part.
- Ducting (What Connects Everything)
You need ducting to carry air to and from the valve.
Most commonly this will be:
- Flexible duct — easiest to work with and what most installers use. The two most common variations is our Industrial grade PVC flexible duct and our insulated flexible duct.
- Spiral duct — sometimes used depending on layout/performance
In most jobs we see, flexible duct is used from the valve back into the system, especially in ceiling voids.
- An Inline Fan (The Bit That Actually Moves Air)
This is what makes the whole thing work.
No fan = no airflow.
A lot of customers we deal with go for the S&P TD Silent range — it’s a solid, reliable option and pretty quiet, which suits residential installs. Our range also includes economy fans and Silent fans with build in timers.
- External Grille or Louvre (Where the Air Goes)
Air has to go somewhere.
So you’ll need:
- An external wall grille – Our Circular Aluminium Grilles are the most popular as they will connect directly to your selected size of duct.
- Or a weather louvre
This is what completes the system — allowing air in or out of the building.
- The Small Bits That Matter
These are the things that often get forgotten.
You’ll need:
- Duct banding to secure the flexible duct
- Pre-cut duct band clips (makes life a lot easier on site) for securing flexible duct to spigots of the vales, fan and exterior grille. Our 20mm-215mm Pre cut duct band clips will work with any size of Rondo or Kvadro.
- Sealant or tape to keep everything airtight
They’re not the exciting parts, but they make a big difference to how well the system performs.
Common Issues We See
Just from experience, the usual problems tend to be:
- Assuming the valve works on its own
- No fan included in the setup
- Flexible duct not secured properly
All simple things — but they’ll cause headaches if missed.
Are They Worth It?
If appearance matters — yes, definitely!
They give you that clean, “invisible” finish that standard vents just can’t match.
But they do need a bit more thought during install compared to a normal valve.
Final Thoughts
The Ergovent Rondo and Ergovent Kvadro diffusers are probably the most popular options we supply for this type of setup, and for good reason — they look the part.
Just keep in mind:
They’re only one piece of the puzzle.
To actually work, you’ll need:
- Flexible ducting
- An inline fan (or central system)
- An external grille or louvre
- Proper fixings and airtight connections
For Instance, a full system order could look like this:
Qty 1x Rondo 100mm
Qty 1x PVC Flexible Duct 100mm
Qty 1x TD Silent Inline fan 100mm
Qty 1x Exterior Grille 100mm
Qty 4x Duct Band Clip (up to 215mm)
Qty 1x Sealant
Fresh Air Supplies supply all of the above, but as always — the full setup should be confirmed by your installer or contractor.
if you have any questions regarding a ventilation set up that includes an invisible / plaster in air valve please get in touch with the Fresh Air Supplies team on +44 (0) 28 86752336 or email sales@freshairsupplies.co.uk