14
If a filter is fitted to the return air grille, it should be easily accessible for regular cleaning.
The chart below gives the minimum recommended return air grille sizes for each model heater.
Table 4:
Minimum Recommended Return Air Grille Selection Chart
Model
Without Filter
With Filter
Grille Size
(mm²)
Example of Size
(mm)
Grille Size
(mm²)
Example of Size
(mm)
BX3 Models
BX315 (300mm)**
0.19
(400x500)
0.28
(400x700)
BX320 (300mm)**
0.22
(400x550)
0.32
(400x800)
BX320 (350mm)**
0.24
(400x600)
0.35
(400x850)
BX326 (350mm)**
0.32
(400x800)
0.46
(400x1150)
BX326 (400mm)**
0.35
(400x900)
0.51
(400x1300)
2PWN Models
2PWN15
0.17
(400x450)
0.25
(400x625)
2PWN20
0.20
(400x500)
0.29
(400x725)
2PWN20 XA
0.22
(400x550)
0.31
(400x775)
2PWN26
0.33
(400x825)
0.48
(400x1200)
2PWN26 XA
0.36
(400x900)
0.52
(400x1300)
DF3 & UF3 Models
DF320 XA
0.28
(400x710)
0.35
(400x870)
UF320 XA
0.25
(400x625)
0.31
(400x760)
UF326 XA
0.36
(400x900)
0.44
(400x1100)
**Model and (Base Box Pop) size
For example a grille with a free ventilation opening measuring 400mm x 650mm, the grille size is 0.40m x 0.65m =
0.26m². This grille would be suitable for a BX320 XA heater provided the grille does not have a filter fitted.
8.0 Outlet Guide
The outlet chart provides recommendations based on using the Brivis "SuperSizeGuide" / Brivisize™ or a system
designed using accepted design principles. These figures also relate to typical size registers and diffusers used on
domestic heating systems i.e. 300mm x 100mm floor registers and 150mm round ceiling diffusers, with 150mm
ductwork connection. For all systems, a minimum number of outlets must remain fully open (this includes both the
outlet grille and the damper in the duct) if the heater is to operate properly without overheating. Similarly, ceiling
outlet systems have a maximum number of outlets that can remain fully open, to ensure that the velocity through
each outlet is sufficient. These maximum ceiling outlet figures relate to fully open outlets, however the system will
operate efficiently with more outlets open, if it has been properly balanced.
Note:
Grille sizes in Table 4 are for Egg-Crate Grilles and are based on airflows at a static pressure of 125 Pa for
26 kW models and 50 Pa for 15 kW and 20 kW models. For all other grille types, consult grille manufacturer's
specifications.
