HJ Cooper Mains Pressure Stainless Steel Indoor Cylinders


Discontinued late 2017

Superseded by the Rinnai Mains Pressure Stainless Steel cylinders.

Connect to a hot water heat pump or solar system with the extra eco inlet connection (excl. the 135 L). 

Install as a low pressure system then connect, without replacing your cylinder, to the luxury of mains pressure when you are ready.


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Product Details


  • Lightweight, stainless steel makes transport and installation a breeze
  • Low maintenance, no sacrificial anode to maintain
  • Future proofed, auto reset thermostat option means these cylinders can be solar and heat pump ready

Innovative design
The 250 and 300 L cylinders have the option of a second element making recovery times quicker and making it less likely you'll run out of hot water.

Suitable for

  • indoor installations only
  • mains and low pressure systems
  • residential and commercial applications
  • left or right hand plumbing connections
  • connection to an open loop solar or hot water heat pump system

Not suitable as a pool or spa heater.

Water quality
HJ Cooper water heaters are manufactured to suit most New Zealand council water supplies. However some water supplies can have a detrimental effect on the water heater, its operation and life expectancy.

Water supplies with a high level of calcium carbonate (hard water) can cause scaling on hot surfaces. We recommend a water temperature of no more than 65 °C to minimise scale build-up. Scale reducing or water softening devices should be considered in hard water areas. The unit is not guaranteed against damage due to scaling. 

Technical Specifications

Capacities and element sizes
  • 135 L 2 and 3 kW
  • 180 L 2 and 3 kW
  • 250 L 2 and 3 kW
  • 300 L 2 and 3 kW

Not required


Hot and cold water connections ¾ " (20 mm)


Inner cylinder- duplex stainless steel
Outer casing - galvanised steel


Incoloy 825 alloy sheath element positioned at the bottom on the tank. Twin element options are available.

Max. working pressure

850 kPa

Pressure testing

To 15 bar

Thermal insulation

CFS-free polyurethane foam compliant with MEPS standard


Robert Shaw 30 A contact thermostat, manually resettable at 85 °C. Thermostat can be upgraded to an auto-reset thermostat for solar and hot water heat pump applications.

TPR valve

Rating of TPR supplied with cylinder—factory set to 850 kPa and 90 °C

Weight empty (approx)
  • 135 L = 29 kg
  • 180 L = 35 kg
  • 250 L = 45 kg
  • 300 L = 53 kg
Cylinder recovery times (theoretical)

Based on a thermostat temp. setting of 60 °C and an incoming water temp. of 15 °C

Model 2 kW 3 kW 2 x 2 kW 2 x 3 kW
135 L 3 hrs 32 mins 2 hrs 22 mins - -
180 L 4 hrs 44 mins 3 hrs 9 mins - -
250 L 6 hrs 34 mins 4 hrs 23 mins 3 hrs 17 mins 2 hrs 11 mins
300 L 7 hrs 53 mins 5 hrs 15 mins 3 hrs 56 mins 2 hrs 39 mins

Late 2017 and superseded by the Rinnai Mains Pressure Stainless Steel cylinders