There is a simple tension in every fume hood. You want enough airflow to keep the operator safe, but airflow costs energy, and running a hood flat out all day, whether or not anyone is using it, is wasteful. Variable air volume is the neat answer to that tension, and applied to a ductless hood it brings the energy benefits without the ductwork.
What VAV actually means
The key measure of a fume hood's protection is its face velocity, the speed at which air is drawn in across the opening. Too slow and fumes can escape; the aim is to hold a steady, safe face velocity whenever the hood is in use.
A traditional hood runs its fan at a fixed speed. When the sash is lowered, the opening is smaller, so the same fan pulls air in faster than needed, wasting energy. A VAV hood is smarter. It senses the sash position, or the airflow, and adjusts the fan speed to match. Lower the sash and it eases off. Raise the sash and it works harder. Throughout, it aims to hold that steady, safe face velocity.
The clever part of VAV is that it saves energy precisely when protection needs less airflow, and never at the expense of the person at the bench.
Why this matters more for a ductless hood
On a ductless hood, the fans are on board and typically low-energy EC or DC types, which respond well to variable speed control. Pairing them with VAV brings a few genuine benefits:
- Energy saving potential. The fan does not run harder than it needs to, so a hood that spends part of its day with the sash down uses less energy over time.
- Quieter working. A fan that eases off when it can is a quieter fan, which makes the hood more pleasant to work at for long sessions.
- Longer filter life, indirectly. Moving only the air you need can help the filter last, since it is not processing more air than necessary.
- Steady protection. The operator still gets a consistent face velocity across sash positions, which is the whole point.
Where a VAV ductless hood makes most sense
- Hoods that are in use on and off through the day, rather than flat out constantly.
- Labs conscious of energy use and running costs.
- Spaces where noise matters, such as teaching rooms and shared labs.
- Anywhere the flexibility of ductless is wanted, but with smarter energy use on top.
Safety is never the trade-off
It is worth being clear on this. VAV is not about running a hood at less than a safe airflow to save money. It is about not running it at more than it needs, while always holding the face velocity that keeps the operator protected. An airflow alarm still watches over the whole thing, so if airflow ever falls below where it should be, the operator knows. Energy saving and safety are working together here, not against each other.
Our Pro range uses variable air volume
This is the technology built into our Pro range. Rather than running at a single fixed speed, the Pro range varies its airflow to hold a steady face velocity as the sash moves, so you get consistent protection with lower energy use and quieter running. If you like the flexibility of ductless and want the smarter energy behaviour of VAV on top, the Pro range is where to look.
The Pro range, with variable air volume
Our Pro range ductless cupboards use VAV control to hold steady protection while easing off on energy and noise when they can.
Honest about the limits
A VAV ductless hood is still a ductless hood, so the same sensible boundaries apply. Filtration suits work the media can genuinely handle, and it is not the right choice for very large volumes, evaporation to dryness, or very highly toxic or unknown chemistry. VAV makes a ductless hood smarter about energy; it does not change what a filter can and cannot hold.