What size hot water system do I need for my home?

A general guide: 1-2 people: 80-125L storage or small continuous flow. 3-4 people: 160-250L or medium continuous flow. 5+ people: 315L+ or large continuous flow system.

Is a continuous flow or storage hot water system better?

Continuous flow systems never run out of hot water and are more efficient for larger households. Storage systems have a lower upfront cost and suit smaller households.

Can ATC Plumbing help me choose the right hot water system?

Yes — we assess your household size, existing connections, and budget to recommend the most suitable system. Call 1300 282 758 for advice.

What Size Hot Water System Do I Need? Melbourne Guide (2026)

Christopher Unwin
May 2
2 min read

Updated: May 3

Why Size Matters — And Why Bigger Isn't Always Better

An undersized hot water system means running out of hot water mid-shower. An oversized one means paying to heat water you never use. Getting the size right when replacing a system is one of the most important decisions — and it's more nuanced than just matching the old tank's capacity, especially if your household has changed.

Sizing for Gas Storage Hot Water Systems

As a general guide for Melbourne households: 1–2 people need a 125–160 litre tank; 3–4 people a 170–250 litre tank; 5+ people a 250–315 litre tank. These assume the system heats continuously or on a timer. If your system only heats once per day (e.g. overnight), err toward the larger size for your household to ensure adequate recovery.

Sizing for Continuous Flow Gas Systems

Continuous flow systems are rated by flow rate in litres per minute (L/min). For Melbourne, where cold water inlet temperatures can drop to 10°C in winter, you need a unit capable of delivering your target temperature at your peak simultaneous usage. A family of 4 with one bathroom typically needs a 16–20 L/min unit. Two simultaneous showers requires 20–26 L/min. Undersizing a continuous flow system means the water won't reach temperature when multiple outlets run at once.

Sizing for Heat Pump Hot Water Systems

Heat pump systems heat more slowly than gas storage, so they need a larger tank. A household of 4 should look at 270–315 litres minimum. In Melbourne's colder months, heat pump efficiency drops — sizing up slightly ensures adequate recovery overnight. Victoria's heat pump rebate program can significantly offset the higher upfront cost.

Don't Just Replace Like-for-Like

If your household has grown, shrunk, or changed habits since your last system was installed, it's worth reassessing the size. ATC Plumbing will recommend the right size for your household and discuss all fuel type options honestly. Call 1300 282 758 for same-day hot water advice or replacement across Melbourne's south-east.