Rinnai 22
Ducted Gas Heater IM
6. DUCTING AND OUTLETS
6.1 DUCT DESIGN AND SIZING
Good duct design and sizing are essential to every Central Heating system. Use the Brivis "SuperSizeGuide"/
Brivisize™ and technical data within this manual for the best results and follow these guidelines:
• Ductwork should be well insulated, airtight and have a minimum insulation rating of R1.O (R1.5 in some areas).
Ensure that ducting complies with the Building Code of Australia
• The ducting should be well fastened to pops, BTO's, outlet boots and neck adapters adequately with duct tape,
in accordance with AS 4254, HB 276 and AS5141.
• It should be correctly sized with the curves and bends smooth enough to ensure the air flows through efficiently
and quietly with minimal resistance
• The registers and diffusers should be large enough and of good design. They should minimise noise, while
providing the correct distribution pattern
• The positive return air system should be fitted with a grille large enough to accept the full air capacity of the
system at low noise levels and minimum resistance
• If the system uses high level outlets (e.g. ceiling diffusers), then the return air inlet should be at a low level.
Ceiling systems with a high level return air may result in reduced performance
NOTE
It is important that the ducting should be well insulated. It is mandatory under building codes to
install insulated, fire rated duct.
6.2 RETURN AIR GRILLE
If a filter is fitted to the return air grille, make sure it is easily accessible for regular cleaning.
Table 4 gives the minimum recommended return air grille sizes for each model heater.
Table 4. Minimum Recommended Return Air Grille Selection
Without Filter
With Filter
Model
Grille Size
(m²)
Example
Size (mm)
Grille Size
(m²)
Example
Size (mm)
BX3C Models
BX315C (300mm)**
0.19
(400x500)
0.28
(400x700)
BX320C (300mm)**
0.22
(400x550)
0.32
(400x800)
BX320C (350mm)**
0.24
(400x600)
0.35
(400x850)
BX326C (350mm)**
0.32
(400x800)
0.46
(400x1150)
BX326C (400mm)**
0.35
(400x900)
0.51
(400x1300)
2PWN Models
2PW15N
0.17
(400x450)
0.25
(400x625)
2PW20N
0.20
(400x500)
0.29
(400x725)
2PW20N XA
0.22
(400x550)
0.31
(400x775)
2PW26N
0.33
(400x825)
0.48
(400x1200)
2PW26N XA
0.36
(400x900)
0.52
(400x1300)
**Model and (Base Box Pop) size
For example a grille with a free ventilation opening measuring 400mm x 600mm, the grille size is 0.40m x 0.60m =
0.24m². This grille would be suitable for a BX320C XA (350mm pops) heater provided the grille does not have a
filter fitted.
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.
