Discontinued Product, please contact 0800 RINNAI for more information

Discontinued Product, please contact 0800 RINNAI for more information

HJ Cooper Stainless Steel Mains Pressure Thermosiphon Single and Twin Coil Hot Water Cylinders

HJ Cooper Stainless Steel Mains Pressure Thermosiphon Single and Twin Coil Hot Water Cylinders

Wetback is something that is mostly associated with an old house with a low pressure copper cylinder connected to an old wood burner. With an HJ Cooper thermosiphon cylinder you can now have a new modern house with mains pressure water heated by your wetback fire, saving you money on your power bill.

Peace of mind
This range of electric mains pressure hot water cylinders comes with a 10 year warranty on the inner cylinder, and is backed by Rinnai after sales service and support.

Thermosiphon coil for wetback
The water is circulated through a coil inside the cylinder by a thermosiphon effect i.e. warmer water rises and cooler water falls, creating a natural flow. This means there is no need for a pump to circulate the water, you can still heat your water even if there’s a power cut!

Single or twin coil?
You will need a twin coil cylinder if you are connecting to a wetback fire and a glycol solar system. If you are connecting to a wetback fire and/or a potable solar system then you will need a single coil hot water cylinder. A single coil cylinder has an extra eco connection that can be connected to an open loop (potable) solar system, or a hot water heat pump.

Twin coil systems: Running cost savings
Save money on power in summer using solar water heating through one coil, and in winter heat the water by the webtback fire with the second coil.

Designed for high temperatures
The duplex stainless steel inner cylinder means it can be used in solar systems with high incoming water temperatures.

Suitable for:
• Indoor installations
• Mains and low pressure systems
• Domestic and commercial water heating applications

Thermosiphon single coil: Suitable for connection to a wetback fire or open loop solar system.
Thermosiphon twin coil: Suitable for connection to a wetback fire and closed loop solar system.

Not suitable as a pool or spa heater, or for underfloor heating.


Model codes and capacities: Single coil MS250550CT20 = 250 L (2 kW)
MS250550CT30 = 250 L (3 kW)
MS300550CT20 = 300 L (2 kW)
MS300550CT30 = 300 L (3 kW)
Model codes and capacities: Twin coil MS250550CCT20 = 250 L (2 kW)
MS250550CCT30 = 250 L (3 kW)
MS300550CCT20 = 300 L (2 kW)
MS300550CCT30 = 300 L (3 kW)
Refer to the Storage Hot Water pocket guide, 'Mains Pressure - Premium Hybrid Thermosiphon - Stainless Steel (Suitable for Wetback), for details on different element configurations and thermostat options.
Construction • High grade duplex stainless steel inner cylinder (refer note below)
• Galvanised steel outer casing
• CFC free polyurethane foam insulation, compliant with NZ MEPS
Connections • Hot and cold water connections ¾ " (20 mm)
• Coil connections ¾ " (20 mm)
Coil description Wetback thermosiphon coil 25 mm diameter. Auxiliary coil 20 mm diameter.
Coil length 11 m (0.86 m²)
Coil kW rating Nominal 22 kW
Element Incoloy 825 alloy sheath element positioned at the bottom of the tank.
• 250 L: 2 kW* or 3 kW
• 300 L: 2 kW* or 3 kW
* Twin element options available
Thermostat Robert Shaw 30 A contact auto reset thermostat
TPR TPR supplied, factory set to 850 kPa and 90 °C
Weight: Single coil 250 L = approx. 49 kg (empty)
300 L = approx. 56 kg (empty)
Weight: Twin coil 250 L = approx. 55 kg (empty)
300 L = approx. 62 kg (empty)
Superseded September 2017, superseded by the Rinnai branded coiled cylinders
General properties of duplex stainless steel 2304
Duplex 2304 is a 23% chromium, 4% nickel, molybdenum-free duplex stainless steel whose structure is a balance of ferritic and austenitic. It has general corrosion resistance similar or better than Alloys 304L and 316L but with yield strength nearly double that of austenitic stainless steels. Its duplex microstructure and low nickel and high chromium contents also allows Duplex 2304 to demonstrate improved stress corrosion resistant properties compared to 304 and 316. It is typically suitable for all applications in the -58 °F to 572 °F 
(-50 °C to 300 °C) temperature range and is designed to feature high mechanical strength, good weldability, good corrosion resistance, high resistance to stress corrosion cracking, good machinability, low thermal expansion, good fatigue properties, high thermal conductivity, and easy fabrication.
[source: http://www.pennstainless.com/stainless-grades/duplex-grades/duplex2304-stainless-steel/]

Mains pressure stainless steel thermosiphon single coil (all dimensions are in mm)
 Mains pressure stainless steel thermosiphon single coil dimensions diagram

Mains pressure stainless steel thermosiphon twin coil (all dimensions are in mm)
 Mains pressure stainless steel thermosiphon twin coil dimensions diagram


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