Heavy Duty Gas Indoor A620260N0 (Natural Gas Only)

Commercial Storage Gas

Model Number: Heavy Duty Gas Indoor A620260N0 (Natural Gas Only)

Rheem Heavy Duty Gas water heaters have been designed to supply large quantities of hot water. The cylinder is protected by multiple anodes and a double layer of vitreous enamel.

  • Designed for greater protection
  • Adjustable thermostats
  • Equa-Flow® system allows for flexibility in installation
  • Available in natural gas only

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Storage Capacity   litres 260
  A mm 1660
  B mm 590
  C mm 670
  D mm 990
  E mm 330
  F mm 297
  G mm 1520
  H degrees 27
  K mm 655
  L mm 295
  M mm 100
  P mm -
Weight - Empty   kg 98
Inlet/Outlet Connections (BSPF)     RP1¼/32
Gas Connection (BSPF)     RP½/15
T&PR Valve Connection (BSPF)     RP¾/20
T&PR Valve Setting   kPa 1000
Expansion Control Valve (ECV)10 Setting   kPa 850
without ECV10 fitted   kPa 800
with ECV10 fitted   kPa 680
Max. Thermostat Setting   °C 65
Factory Thermostat Setting   °C 60
Min. Thermostat Setting   °C off
Manifold - Min. Centre to Centre   mm 845
Electrical Connection     -
Electrical Rating 240V 50Hz     -

No. of Units
in Parallel
Initial Storage
Thermal Input Litres hot water at 50°C rise over peak period (based on natural gas)
  (Litres) (MJ/h) 1 hour 2 hours 3 hours 4 hours 6 hours 8 hours
1 260 50 380 570 760 950 1330 1700
2 520 100 770 1140 1520 1900 2650 3410
3 780 150 1150 1720 2280 2850 3980 5110

Operations at temperatures above 80°C

Rheem commercial gas models 621 265, 631 265, 621 275, 631 275 are designed to operate at temperatures up to 82°C for sanitising and other applications.

Where the water supplied by the water heater is required consistently at any temperature above 80°C, we strongly recommend you use a pumped recirculation system. (Please refer to the Equa-Flow® section.)

Gas pipe supply

The gas supply piping should be sized in accordance with AS/NZS 5601.1.

The gas supply pipe must be sized so that the minimum gas pressure is available at the inlet to each water heater when all appliances are operating at maximum gas consumption.

The minimum gas pressures are 1.13 kPa for natural and SNG, 2.75 kPa for LPG and 0.75 kPa for town gas and TLP.

  • Please note this model is available in natural gas only.
  • Technical information on propane & butane models has been shown below for reference purposes only. 
Gas Type   Nat/SNG Propane Butane
Thermal Input MJ/h 50 47 39
Output kW 11.0 10.3 8.6
Min. Gas Supply Pressure kPa 1.13 2.75 2.75
Test Point Pressure kPa 1.00 2.70 2.70
Max. Gas Supply Pressure kPa 3.5 3.5 3.5
Litres Recovery Per Hour at Rise of 20°C 480 450 370
  30°C 320 300 250
  40°C 240 230 190
  50°C 190 180 150
  60°C 160 150 130
  65°C 150 140 120
  70°C 140 130 110
  75°C 130 120 100

Approximate daily energy consumption

These daily gas consumption figures are approximate. They’re based on:

  • A daily usage of hot water per water heater in litres, at 50°C rise
  • Using natural gas, but they can be used with reasonable accuracy for other gas types
  • Mains pressure supply systems only

The figures do not allow for pipe heat losses. An additional allowance must be made for large manifold systems and installations designed with a circulated flow and return system.

Use the table to calculate

  • The approximate energy cost for a particular installation
  • The average daily hot water consumption when the energy consumption is known
Daily Hot Water Usage @ 50°C Temp Rise Energy Content of Hot Water Approximate Energy Used Per Day Natural Gas
(Litres) (MJ) (MJ)
0 0 33.9
50 10.5 47.1
100 20.9 60.3
150 31.4 73.5
200 41.9 86.7
250 52.3 99.9
300 62.8 113.0
350 73.3 126.2
400 83.7 139.4
450 94.2 152.6
500 104.7 165.8
600 125.6 192.2
700 146.5 218.6
800 167.4 245.0
900 188.4 271.4
1000 209.3 297.8
1250 261.6 363.8
1500 314 429.8
1750 366.3 495.8
2000 418.6 -
2500 523.3 -
3000 627.9 -
3500 732.6 -
4000 837.2 -
5000 1046.5 -

To convert to kg of Propane, divide MJ by 49.5. To convert to litres of Propane, divide MJ by 25.3.

Ventilation for indoor gas water heaters

It’s a requirement of AS/NZS 5601.1. that indoor gas water heaters (non room sealed) are installed in a location with adequate ventilation.

Two permanent openings are required into the room housing the water heaters.

The distance from the top of the upper opening to the ceiling and from the bottom of the lower opening to the floor, cannot each exceed 5% of the room height.

The two openings can be combined, as long as the top and bottom of the opening are within the 5% distance requirement.

The minimum vertical dimension of any free ventilation opening is 6mm.

The minimum free ventilation area of each opening required for each Rheem commercial gas water heater installed is shown in the table.

Please refer to AS/NZS 5601.1. for full details of the requirements.


  1. Although a room sealed water heater installation draws the air required for combustion from outside, ventilation may be necessary to prevent a rise in the ambient temperature in the room.
  2. In plant rooms, wherever possible more than one wall should be used to provide ventilation. This allows a flow of air across the room and helps prevent excessive temperatures in the room.
  3. In rooms other than plant rooms, ventilation is required if the total thermal input of the water heaters exceeds 3 MJ/h per cubic metre of room volume.
  4. AS/NZS 5601.1. should be consulted for further requirements when ventilating through adjacent rooms to the water heater installation.
  Natural Ventilation
(Area of Each Opening Per Water Heater)
Mechanical Ventilation
(Per Water Heater)
  Location of Water Heater      
  Plant Room Non Plant Room Low Level High Level
Direct to
via Adjacent
Direct to
via Adjacent
Air Supply
MJ/h (cm2) (cm2) (cm2) (cm2) (L/s) (L/s) (cm2)
50 75 150 150 300 25 8 75

Natural air supply with a mechanical exhaust is not permitted.

Power fluing

You can either install an individual Rheem gas model or a bank of multiple 621 265, 621 275 models with a power flue.

It’s essential to prove the flue system operates correctly before the main burner is allowed to operate.

How do you achieve this? A self proving relay interconnected with either a vane switch or pressure differential switch will prove both air flow and functionality of the control circuit before ignition of the main burner.

Please refer to AS/NZS 5601.1. for full details of what’s required.

For multiple installations, the operating principle is the same as for a single water heater.

Any water heater can switch on the fan, and the burners can only come on when the sail switch is closed.

Intermittent PowerFlue Fan Control – Multiple Water Heater Rheem 621 Series & Raypak Type B Series.

Fluing: indoor gas water heaters

Rheem indoor gas water heaters are designed for connection to a flue system in accordance with the requirements of AS/NZS 5601.1.

Manifolded water heaters can either be flued individually or connected to a common flue. The design of the flue must comply with Appendix H of the Standard.

AS/NZS 5601.1. states the vertical rise directly out of the water heater must be the maximum possible height before any change in direction.

Also, the total length of the lateral (horizontal) section must be as short as possible, not exceeding 50% of the total flue height of the system.

The table and diagram below are extracted from the Flue Tables in AS/NZS 5601.1. and are meant as a quick guide only. Any variations should be referenced from AS/NZS 5601.1..

Appropriate authorities should be consulted before any work is commenced on flues other than single appliance flues.

Multiple Manifold Flue System

    1 2 4 6 8
  Total Flue Height Max. Lateral Flue Dia Max. Manifold Flue Dia Max. Manifold Flue Dia Max. Manifold Flue Dia Max. Manifold Flue Dia
  (H)     Length (A)   Length (A)   Length (A)   Length (A)  
Model (m) (m) (mm) (m) (mm) (m) (mm) (m) (mm) (m) (mm)
620 260 2 1 100 1 125 - - - - - -
50 MJ/h 3 1.5 100 1.5 125 - - - - - -
  6 3 100 3 125 3 150 - - - -
  12 6 100 6 100 6 150 6 175 - -
  24 7.6 150 12 150 12 150 12 150 12 175


  • The table is based on a natural draft system with an insulated type flue or a flue installed indoors
  • The table is extracted from the Flue Tables in AS/NZS 5601.1. and is meant as a quick guide only. Any variations should be referenced from AS/NZS 5601.1.

Technical Documents

Performance Calculator View Online
Sample Specification View Online
Manifolding View Online
Product Drawings - 1 Unit Download
Product Drawings - 2 Units Download
Product Drawings - 3 Units Download
Product Drawings - 4 Units Download
Product Drawings - 5 Units Download
Product Drawings - 6 Units Download
Product Drawings - 7 Units Download
Product Drawings - 8 Units Download
Installation Instructions Download
Brochure Download