Products
Airflow Dilution Fans

AIRFLOW dilution and flue boost fans are manufactured in the United Kingdom and distributed in Australia by Hunt Boilers.

The range is available in standard form (GBDF series) typically used with atmospheric boilers and water heaters of around 75% efficiency.

In addition, an enhanced corrosion resistant version is available (SSDF series) incorporating stainless steel fan cases.  These are ideally suited for installation into stainless steel ducting, higher efficiency boilers, or any boiler likely to produce condensation as part of its normal operation.

The key features of the product range include:

  • Flexibility to install into new or existing plant rooms
  • In line fan installation for the HDF1 series
  • Eliminates the need for more expensive larger diameter or external flues
  • Provides an alternative to the refurbishment of current flue installations
  • Efficient and quiet operation capable of overcoming system resistance in flue ducts
  • Inbuilt vane switch with position proving capability, that causes boiler shut down in the event of a fan failure
  • High levels of protection with the use of stainless steel on the SSDF series, and Aluzinc coated steel on the HDF1 and GBDF series
  • Fresh air added into the boiler's discharge flue duct which dilutes the flue gases, making them more suitable for disbursement at low levels
  •      

Choosing the Correct Dilution Fan

The fan selection depends on the airflow required to dilute the combustion products to a safe level and/or the pressure loss in the ductwork system that the fan has to overcome.

Note: The dilution calculations offered are based on reducing the CO2 content to 1% and should be used in conjunction with all requirements contained within AS/NZS 5601.1 for Gas Installations.

To select the appropriate fan for your application follow these easy steps.

Step 1: Determine the Flow Rate required

The required volume flow rate of diluted flue gases necessary for a given boiler can be calculated as follows:

Flow Rate in Litres per Second (L/s) = 3.6 x rated input of boiler in kW

Step 2: Determine the Flue Pressure Resistance

Part 1 - Straight Section

First, you must determine the flue pressure resistance in all the straight sections of the ductwork.

Add up the total length of straight sections of ductwork. Multiply this total length by the pressure loss per metre of duct which you can determine from the following table.

(Note: If you have square duct instead of round, use the column for the next smaller round duct as an approximation, i.e. For 350 square duct you would use the figure for 300 round duct.)

Part 2 - Bends

Second, you must determine the flue pressure resistance in all the bends.

Loss Coefficient KL = (number of bends x 1.2) + 5.0

(Note: This formula already incorporates an allowance for a low restriction grille in the entry and the exit. If you have other restrictions in the ductwork (e.g. hats over the ends of the ducts, then you need to allow for these separately)

Pressure Loss (bends) = 760 x Flow Rate (L/s) x Loss Coefficient (KL) / Flue Dia. (mm) Squared

Therefore Total Flue Pressure Resistance = result from part 1 + result from part 2

Once you have determined the Flow Rate Required and Flue Pressure Resistance, use the following table to select the appropriate fan model.

Flue Pressure Resistance for Straight Sections (Pascals per metre)

Flue Diameter (mm)
175 200 250 300 350 400 500 600
100 L/sec 1.40 0.75 0.24 0.10 0.10 0.10 0.10 0.10
200 L/sec 5.00 3.20 0.90 0.36 0.17 0.10 0.10 0.10
300 L/sec 5.75 5.75 1.90 0.75 0.35 0.19 0.10 0.10
400 L/sec 12.0 10.0 3.40 1.30 0.60 0.32 0.10 0.10
500 L/sec 19.0 18.0 5.00 2.00 0.90 0.48 0.16 0.10
600 L/sec     7.00 2.80 1.30 0.70 0.22 0.10
700 L/sec 9.00 3.80 1.70 0.90 0.30 0.12
800 L/sec 11.0 5.00 2.20 1.20 0.37 0.15
900 L/sec 15.0 6.00 2.80 1.50 0.48 0.19
1000 L/sec 18.5 7.50 3.40 1.80 0.55 0.24
1200 L/sec   11.0 4.50 2.50 0.80 0.32
1400 L/sec 14.0 6.50 4.20 1.10 0.44

 

General Product Specifications
Flue Pressure Resistance (Pascals)
Model
Motor Voltage
Motor watts
 
0
10
20
30
40
50
60
70
80
90
100
110
120
GBDF2/SSDF2
240v
75
L/s
300
290
280
260
250
240
230
220
190
140
80
40
0
GBDF3/SSDF3
240v
120
L/s
600
580
570
560
540
520
510
500
480
460
440
410
380
GBDF4/SSDF4
240v
335
L/s
1000
985
970
950
935
920
900
880
860
840
815
780
760
GBDF5/SSDF5
415v
900
L/s
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
1400
1370
1350
1325
GBDF6/SSDF6
415v
900
L/s
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
 
130
140
160
180
200
225
250
275
300
325
350
 
GBDF2/SSDF2
240v
75
L/s
0
0
0
0
0
0
0
0
0
0
0
GBDF3/SSDF3
240v
120
L/s
320
280
120
40
0
0
0
0
0
0
0
GBDF4/SSDF4
240v
335
L/s
740
710
640
520
340
200
80
0
0
0
0
GBDF5/SSDF5
415v
900
L/s
1300
1260
1200
1150
1075
975
850
450
200
80
0
GBDF6/SSDF6
415v
900
L/s
n/a
n/a
n/a
1750
1675
1570
1420
1280
1085
850
620
Model SSDF2 in standard trim, suitable for Natural Gas non-condensing boilersAll AIRLOW dilution fans are supplied with pressure proving safety interlocksModel SSDF2 in Stainless Steel trim, suitable for Natural Gas condensing boilers
© 2017 Hunt Boilers. All rights reserved.