181J Roof Top Solar: Key Attributes

Key Features

The Solahart J Series is a roof mounted, closed circuit solar water heater specifically designed to provide economical service in medium to high solar gain areas. It is recommended for use in frost or poor water chemistry areas.

The J Series features Solahart's revolutionary multi-flow collector to extract the maximum amount of energy from the sun. This is used to heat the Hartgard fluid in the collector which rises into the heat exchanger where the heat is transferred to the water inside of the tank. The ceramic lined tank has a protective anode and the SP Free Heat series features additional protection.

  •  Space saving roof mount design
  •  Reliable, low maintenance operation
  •  Can cut water heating energy use by up to 55%^
  •  Reduces household greenhouse emissions

 ^ Energy savings of up to 60% shown is based on Australian Government approved TRNSYS simulation modelling of a Solahart 181J and using a small load in Zone 3 and apply when replacing an electric water heater. Any savings will vary depending upon your location, type of Solahart system installed, orientation and inclination of the solar collectors, type of water heater being replaced, hot water consumption and fuel tariff. Maximum financial savings off your hot water bill are achievable when replacing an electric water heater on continuous tariff.

† Solahart Warranty Details: 5/5/5 warranty; 5 year cylinder and collectors supply, 5 year parts, 5 year labour. 10/5/5 warranty, 10 year cylinder and collectors supply, 5 year parts, 5 year labour.

Thermosiphon J Closed Circuit Systems
System Model 181J
Tank Model 180J
Storage Capacity 180 litres
Boost Capacity  90 litres
Weight Empty Tank Only  69 kg 
Weight Full Tank Only  249 kg 
A-Width* Tank Only  1.62 m
Weight Empty System  119 kg 
Weight Full System 312 kg 
A-Width* System 1.62 m

* For servicing and safe access, a space equal to the tank length should be left on the water connection end of the system and 1m (40in) should be left on the three other sides of the installation. ‡HartStat OTP is optional on these models. Systems can be installed as a solar preheater with an inline Solahart gas booster water heater. Refer to the Solahart gas booster specification sheet for further details on the gas booster. 

Collectors J
Aperture area 1.87 m2
Length 1943 mm
Width 1027 mm
Height 83 mm
Capacity 4 litres
Weight Empty 47 kg
Weight Full 51 kg
Working Pressure  
no OTP 80 kPa 
with OTP 170 kPa 
Absorber Surface Black polyester powder coat
Absorber/Riser Material steel
Number of Risers 35
Frame Material aluminium
Insulation Material (Base) 38 mm polyester blanket
Glass 3.2 mm tempered low iron


Water Supply
TPR Valve Setting 1000 kPa
ECV* Setting 850 kPa
Maximum Supply Pressure  
With ECV 680 kPa
Without ECV 800 kPa
Water Connections  
 Cold Rp 3/4
 Hot R 1/2

*Expansion Control Valve. 

Electric Boost Specifications
Heating Unit Type Copper sheath immersion element
Supply Voltage 220 V - 250 V
Recovery Rate @ 240 V and Temperature Rise of:
1.8 51  39  31 
2.4 10  68  52  41 
3.6 15  103  77  62 
4.8 20 137 103 83




How Roof Top Solar Systems Work

Solar Operation

The 181J solar system has its vitreous enamel lined solar storage tank installed on the roof directly coupled to the solar collectors. In the Closed Circuit Series, heat is absorbed by the collector and passed to the ‘Hartgard’ heat transfer liquid inside the collector. As the temperature of the ‘Hartgard’ increases, the hot fluid rises up through the collector by the Natural Thermosiphon Principle, into the heat exchanger jacket around the potable water storage tank. Here, the heat is transferred to the potable water, cooling the ‘Hartgard’ fluid. The cooler fluid is then forced back down into the collectors through the displacement action of further hot fluid rising up into the heat exchanger jacket.

Orientation of Solar Collectors

To help maximise system performance, solar collectors should be installed with an optimum orientation facing true north (in the southern hemisphere) or true south (in the northern hemisphere). Always check for true north or true south using a compass or other suitable device.

To help maximise system performance, solar collectors should be installed with an optimum inclination. This is equal to 90% to 100% of the local latitude angle when collectors are oriented within 60° of true north or true south, and between 10° and 20° if the collectors are oriented between 60° and 90° from the optimum orientation. Generally, improved summer performance is obtained from an angle of inclination less than the optimum angle and improved winter performance is obtained by an angle of inclination greater than the optimum angle. If the angle of inclination varies by 20° from the optimum angle, the solar collectors will receive about 10% less total annual solar radiation.

Frost/Freeze Protection

Solahart Closed Circuit Systems are protected against freezing or harsh water conditions by our exclusive ‘Hartgard’ fluid. ‘Hartgard’ is a blue, non-toxic, propylene glycol fluid which, when mixed with water, provides the Heat Transfer Fluid contained in the solar collectors and the heat exchanger jacket around the tank. ‘Hartgard’ is used to lower the freezing temperature of the Heat Transfer Fluid and so provides protection against freezing (Note: for the correct % of Hartgard in the Heat Transfer Fluid, refer to the section on Frost / Freeze Protection). ‘Hartgard’ is a special food grade solution and is the only solution permitted to be used in the closed circuit systems. Hartgard has been approved by the National Health and Medical Research Council of Australia.

Solar Boosting

In-Tank Boosting

An isolating switch is installed in the electrical meter box for an electrically in-tank boosted model. This should be left switched on to allow the booster heating unit to operate if required. The booster heating unit is for heating the water at times of low solar energy gain, such as during very cloudy or rainy weather, or during the colder months. The booster heating unit will only activate if heating is required and power is available from the switchboard. When the water is below the thermostat setting, the booster heating unit will turn on and heat the water. The booster heating unit will automatically turn off when the temperature of the water reaches the thermostat setting. If the water temperature drops below the setting again the booster will re-activate.

In-Series Gas Boosting

An in-series gas booster (also known as a continuous gas booster) can be installed between the solar water heater and the hot outlets in the house. This booster should be permanently active. The booster senses the temperature of the water passing through it: if the water temperature is above its temperature setting it does nothing; if below it will automatically heat the water up to the preset outlet temperature setting. This gas booster ensures hot water delivery for a variety of hot water demands without the need for user intervention while enabling maximum solar energy contribution to the water heating. For more information on this booster, consult the owner’s manual for the product.

Over-Temperature Protection System

The Closed Circuit Series solar water heaters have a means of controlling the maximum temperature of the water in the storage tank. These systems may be installed with a ‘HartStat’ valve located between the hot outlet of the collectors and the inlet to the tank heat exchanger. This valve closes when the tank has reached a sufficiently high temperature, thereby preventing further heat transfer to the tank, and thus limiting its temperature.


Why Solahart Solar Hot Water Systems: Download

Solahart 181J Solar Hot Water System Brochure: Download

Solahart In-Line Gas Booster Brochure: Download

Installation Manuals

Solahart On-Roof Solar Hot Water System Owner's Guide and Installation Manual: Download

Solahart In-line Gas Booster Owner's Guide and Installation Manual: Download