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Halton PRL – Plenum for grilles

This balancing plenum connects grilles to the ductwork, equalises the airflow by reducing the velocity – while air is spread evenly into the grille, thus ensuring proper function. It also has efficient sound attenuation, robust and air-tight construction, and wide range of available sizes.

  • Plenum for connecting supply/exhaust grille to ductwork
  • Flexibility for grille installation due to telescopic collar
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  • Plenum for connecting supply/exhaust grille to ductwork
  • Ensures proper function of the supply air grille
  • Robust, airtight construction with aesthetically pleasing design
  • Flexibility for grille installation due to telescopic collar
  • Detachable measurement (only supply air) and airflow rate adjustment module
  • Effective sound attenuation
  • Access for ductwork cleaning


200×100 208 201 198 124 92..150 9 42 101 230 63
300×100 224 301 226 159 92..150 9 33 101 330 63
400×100 260 401 226 159 92..150 9 51 101 430 63
500×100 287 501 276 199 92..150 9 44 101 530 63
300×150 287 301 276 199 92..150 9 44 151 330 63
400×150 360 401 330 249 92..150 9 56 151 430 63
500×150 360 501 330 249 92..150 9 56 151 530 63
600×150 360 601 330 249 92.. 150 9 56 151 630 63
800×150 413 801 382 314 92..150 9 50 151 830 63
400×200 360 401 330 249 92..150 9 56 201 430 63
500×200 394 501 382 314 92..150 9 40 201 530 63
600×200 413 601 382 314 92.. 150 9 50 201 630 63
800×200 413 801 382 314 92..150 9 50 201 830 63

No special dimensions available.


 Part  Material  Note
 Casing  Galvanised steel
 Collar  Galvanised steel
 Attenuation material  Mineral wool  Alternatively polyester fibre
 Spigot with gasket  Galvanised steel  Gasket rubber compound
Measurement and
adjustment module
 Body: Aluminium
 Plate: Galvanised steel
 Brackets: Galvanised steel
 Plastic parts: Polypropylene (PP)
 Spindle: Stainless steel


 Accessory Code  Description
Airflow measurement and
adjustment unit
MSM Adjustment and measurement
module for supply airflow rate
 Airflow adjustment unit MEM Adjustment module for exhaust airflow rate
 Sound attenuation IN Internal sound attenuation material
of mineral wool or polyester fibre

Product models

Model Supply
(with MSM)
(with MEM)
PRL/A Yes No left/right Yes
PRL/B Yes No back Yes
PRL/C Yes No top/bottom Yes
PRL/D No Yes left/right Yes
PRL/E No Yes back Yes
PRL/F No Yes top/bottom Yes
PRL/G No No left/right No
PRL/H No No back No
PRL/I No No top/bottom No

When using Halton PRL with Halton EVA exhaust unit, the plenum will delivered without telescopic collar (order code: ES=Y)

Duct connections

Fig.1. Halton PRL/A, PRL/D or PRL/G (side connection)

Halton PRL/B, PRL/E or PRL/H (back connection)

Halton PRL/C, PRL/F or PRL/I (top/bottom connection)


Halton PRL balancing plenum equalises the airflow by reducing the flow velocity.

Air is spread evenly into the grille, ensuring proper function.

A range of grilles can be connected to the distribution duct with the aid of a Halton PRL, improving their characteristics considerably.

The plenum also attenuates duct noise.

Halton PRL can also be used as an exhaust unit.


Halton PRL is connected to the duct with a spigot equipped with a gasket. The duct connection can be located on the side, above/below or behind the plenum. Due to the symmetrical structure of the Halton PRL, connections can be made in a number of different ways: by turning the plenum right or left, or by rotating, from above or below.

The telescopic collar of the plenum permits mounting into walls of thickness 90…150 mm.
For installation with Halton EVA exhaust unit no telescopic collar is used (not included to delivery).

The recommended safety distance upstream of the plenum in supply installations is minimum 3D.

Dimensions for installation hole are (H+5mm) x (B+5mm).


The supply flow rate is determined by using the measurement and adjustment module MSM.

The tubes and control spindle are passed through the grille. Measure the differential pressure with a manometer. The flow rate is calculated using the formula below.

∆pm      Measured pressure [Pa]
k           The k factor given as a function of mounting and diameter
qv          Airflow rate [l/s]

The k-factor for installations with different safety distances
(D = duct diameter)

PRL > 8xD min. 3xD
200×100-125 8.2 12.6
300×100-160 14.1 21.7
400×100-160 17.7 21.7
500×100-200 34.6 33.9
300×150-200 20.1 33.9
400×150-250 30.0 55.5
500×150-250 34.6 50.1
800×150-315 34.6 83.3
400×200-315 55.9 55.5
500×200-315 27.4 83.3
800×200-315 50.0 83.3

Adjust the airflow rate by rotating the control spindle until the desired setting is achieved.
Lock the damper position with a screw. Replace the tubes and spindle into the plenum.


Detach the grille and the perforated plate of the telescopic collar. Detach the measurement and adjustment module by pulling gently from the casing (not from the control spindle or measurement tubes). Wipe the parts with a damp cloth, instead of immersing in water.

The measurement and adjustment module is remounted by pushing the body until it meets the stopper.

The sound attenuation material within the plenum can also be removed (the material is washable), to enable cleaning of the inner side of the plenum. The material is detached by releasing the retaining brackets, which are replaced after washing.
Replace the grille after cleaning.


The Halton PRL balancing plenum for grilles is made of galvanised steel and has a robust and airtight construction.
Airflow rate measurement and adjustment module are available for supply application. The measurement and adjustment module is adjustable without opening the grille.

The balancing plenum has a spigot with integral gasket for airtight duct connection and a plug for ductwork pressure testing. The Halton PRL plenum has options for duct connection on the side, back or top.
The balancing plenum attenuates duct noise. The sound attenuation material is either mineral wool or polyester fibre with a washable surface.

Order code


S  = Model
A     Supply inlet              (Left-Right connection)
B     Supply inlet              (Back connection)
C     Supply inlet              (Top/Bottom connection)
D     Exhaust outlet          (Left-Right connection)
E     Exhaust outlet          (Back connection)
F     Exhaust outlet          (Top/Bottom connection)
G     No accessories        (Left – Right connection)
H     No accessories        (Back connection)
I       No accessories        (Top/Bottom) connection

W = Width of grille connection (mm)
200, 300, 400, 500, 600, 800

H = Height of grille connection (mm)
100, 150, 200

D = Connection size of duct (mm)
125, 160, 200, 250, 315

Other options and accessories

ES  =  EVA model
N       No
Y        Yes

AT  = Sound attenuation material
P         Polyester fibre
W       Mineral wool
NA      No sound attenuation

OM = Measurement/adjustment modul
YS      MSM installed (supply)
YE      MEM installed (exhaust)
NA     No measurement or adjustment module

ZT  = Tailored product
N       No
Y       Yes (ETO)

Code example

PRL/A-200-100-125, ES=N, AT=P, OM=YS, ZT=N


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