What size hot water system do I need?

Typical sizes for a household of four

Each person uses roughly 50 litres of hot water a day, according to CHOICE, and more with long showers or warm washes. Use the table as a starting point, then adjust for your household.

Why the tariff changes the size

An electric tank on a continuous tariff reheats whenever water is used, so a smaller tank can keep up. An off-peak tank only heats during the tariff's set hours, often overnight, so it has to hold the whole day's hot water. That's why an off-peak tank for the same family is roughly twice the size.

Sizing a continuous flow unit

Continuous flow units never run out, but they can only heat so many litres per minute. Size them by how many outlets run at once, not by how many people live in the home:

• One bathroom: around 16 to 20 litres per minute.
• Two bathrooms: around 20 to 26 litres per minute, so two showers can run together.
• Three or more bathrooms: 26 litres per minute or more, or two units linked together.

Signs your current system is too small

• The last person to shower in the morning gets cold water.
• Hot water runs out when the dishwasher or washing machine is on.
• Your household has grown since the system went in.
• A continuous flow unit goes lukewarm when two showers run at once.

Running out can also be a fault rather than the size. Our guide on why hot water runs out fast covers the common causes.

Bigger isn't always better

An oversized tank costs more to buy and loses more heat sitting idle. If you're replacing a system, it's worth matching it to how you use hot water now, not how you used it ten years ago. We confirm the right size on site before we quote. See hot water replacement.