Set of 2 Temperature and Pressure Guages. 1/2" NPT.
One of these should be placed at the hot water heating exit and one after the heat exchanger. These guages will help you balance your flow and heating levels. Typically your heater should output 140-150F water and after the heat exchanger the return water should be around 70F, if you are using the Greenlife Aquaponics Heat Exchanger.