PLINE vs LINE Diffusers: Which Frameless Linear Slot Diffuser Do You Need?

Ventmann makes two frameless linear slot diffusers that look almost identical once they're plastered in and painted: LINE and PLINE (Performance Line). Both are made from gypsum, both disappear into the ceiling, and both install the same way. The difference is what happens to the air as it leaves the slot — and that decides which one belongs where.

The short answer

What they have in common

PLINE — Performance Line

LINE

• Gypsum construction — plastered in flush and painted with the ceiling, so only the slot remains.
• 1, 2 or 3 slots in 625, 1000 and 1250 mm lengths, for ceilings or walls.
• The same installation sequence — temporary battens, pre-assembled diffuser, plenum and spigot, cut board, joint, sand and paint. One PLINE/LINE installation guide covers both.
• The same plenum boxes — the GTG acoustic plenum for top-entry ducts and the VTBOX insulated thermo box for side entry.
• 90° corner pieces for continuous perimeter slots, Revit BIM objects, a 5-year warranty and next-day UK delivery.

The real difference: the airflow profile

LINE uses straight-sided slots. The airflow pattern from each slot can be adjusted, so air can be directed vertically or at an angle, and an airflow regulator is available for 18 mm slots when you need finer control during commissioning. It's a precise, flexible slot that suits both supply and extract.

PLINE is engineered around the airflow itself. The curved inner faces of the grille direct air to either side of the unit, and the Coandă effect makes that air attach to the surrounding ceiling or wall. The result is wide dispersal with less perceptible airflow in the room — exactly what you want above a sofa, a desk or a bed.

PLINE ships with a deflector, a perforated deflector is available, and it can also run without one — three ways to tune how air leaves the slot for the room and airflow you're designing for.

PLINE deflector options: standard, perforated or none.

Side-by-side comparison

	LINE	PLINE (Performance Line)
Airflow profile	Straight-sided slots, adjustable pattern	Curved inner faces split air either side (Coandă)
Slot width	12 mm or 18 mm	One Performance profile
Slots / lengths	1–3 slots · 625, 1000, 1250 mm	1–3 slots · 625, 1000, 1250 mm
Airflow accessories	Airflow regulator (18 mm slots)	Standard or perforated deflector, removable
BIM objects	6 Revit families (1–3 slots × 12/18 mm)	3 Revit families (1–3 slots)
Price from (excl. VAT)	£125.00	£148.11
Recognition	—	Red Dot award-winning design
Best for	Extract, slimmest sightlines, long runs	Supply where comfort matters

See them on their product pages: Performance Line (PLINE) and Line (LINE). Trade customers see account pricing when logged in.

Where each one belongs

Choose PLINE for

• Supply to living rooms, bedrooms and offices, where people sit or sleep near the diffuser.
• Long, open-plan spaces that need wide coverage from a single slot run — along glazing, for example.
• MVHR and air-conditioning supply where cooler air shouldn't drop straight down onto occupants.

Choose LINE for

• Extract from kitchens, bathrooms and utility rooms, where the air is drawn in rather than thrown.
• The slimmest sightline — the 12 mm slot is the most discreet line in the range.
• Many metres of slot on a budget, and projects that need fine balancing with the airflow regulator.

Specifying tips

• Size from airflow, not looks. The Product Selector filters by series, airflow, noise, pressure drop, length and number of slots.
• Pick the plenum by duct entry — top entry or side entry — and check our plenum box installation guide.
• Plan runs on the reflected ceiling plan alongside joists, lights and joints, and use 90° corners for continuous perimeter lines.
• See it before you specify — a PLINE 2-slot sample is available.

Quick answers

Is PLINE quieter than LINE?

PLINE's profile is designed to reduce perceptible airflow and turbulence, but real noise depends on airflow, plenum and sizing. Compare the published data for your flow rate in the Product Selector.

Can LINE be used for supply?

Yes. LINE works for supply and extract, and its airflow pattern can be adjusted. Choose PLINE when wide, draught-free dispersal is the priority.

Do they install differently?

No. Both use the same sequence, the same installation guide and the same plenum boxes — so you can mix them on one project without changing the drylining process.