Free tool
What size hot water system do I need?
Most guides count bedrooms. This one counts showers.
Power
Heats whenever it needs to. Size it to the busiest run of showers.
Tank size to look for
160-170 L
It has to hold about 111 L for that run of showers. You only get ~80% of a tank before the top goes cold.
- Each shower pulls from the tank
- 37 L
- Whole day, all uses
- 199 L
- Full reheat from cold
- 6.3 hrs
A 9 L/min head at 41°C only draws about 4.6 L/min out of the tank - the rest is cold mains. Sizing on the head's flow rate is why people buy a tank half again as big as they need.
Now see what each type costs to runAn estimate, on Brisbane mains at about 21°C and a tank at 60°C. Your actual draw depends on the house. If it lands on the line between two sizes, go up - nobody has ever complained about too much hot water.