System Sizing — AUX PRO

Heat pump

AUX R290 unit

1 · Minimum water volume

AUX asks for at least 40 L of water in the system, not counting the water inside the unit. Count only the part that is always open — with every zone valve and TRV that can close, closed.

Water always open litres — pipework, open radiators/loops, buffer

2 · Expansion vessel

The unit has a built-in 5 L vessel, 1.0 bar pre-charge. Check whether the whole system needs more.

Total system volume litres, everything Highest flow temperature °C Height to top of system m above the vessel Relief valve setting bar

3 · Hot water cylinder

People in the home Use per person per day litres at 60 °C Coil type

Figures from the AUX R290 Installation & Commissioning Manual (sections 2.6, 2.7 and 9.4.2). The expansion vessel uses the standard sizing formula for water; for glycol systems use the vessel maker's data, as glycol expands more.