What size hot-water heat pump do I need?

silvereyecomms
Aug 2
2 min read

2 August 2025

Picking the right size hot-water heat pump matters. Too small and you’ll run out of hot water just when you need it. Too big and you’ve spent more than you needed.

The sweet spot depends on your household size, lifestyle, and habits.

Rules of thumb

· 1–2 people: 180–200 L

· 3–4 people: 250–300 L

· 5+ people: 300–315 L+

These are good starting points. But they’re just that—starting points.

Got teenagers who love long showers? Go up a size. Enjoy deep baths? Go up a size. Mostly short showers and minimal laundry? You might get away with smaller.

Recovery time explained

Recovery time is how long it takes to heat the tank back up once it’s been drained. A simple formula gives you the estimate:

ΔT (temperature rise) × volume ÷ heat-pump output = recovery hours.

For example:

· 200 L tank

· 40 °C rise (cold water at 10 °C up to 50 °C)

· 3 kW heat pump

That comes out at roughly 2.5 hours to re-heat from cold.

In real life, you rarely drain the full tank. But it’s a handy way to compare models.

Real-world factors

· Ambient temperature: colder mornings slow heating.

· Set-point temperature: aiming for 60 °C instead of 50 °C adds time.

· Legionella cycle: every so often the unit runs hotter for safety.

All these affect how fast your tank recovers.

Household scenarios

Couple in a flat

A 180 L tank is usually fine. If you both love long hot baths, step up to 200 L.

Family with two kids

A 250–300 L tank gives breathing room for laundry, dishes, and back-to-back showers.

Share house

Five people with different schedules? Go large. A 315 L tank with a higher-output unit avoids morning queues.

Rural home

Long pipe runs or extra laundry from farm work? Oversize slightly to be safe.

The bottom line

A heat-pump hot water system is an investment you’ll live with for years. Choosing the right size means comfort, efficiency, and no cold surprises.

👉 Book a sizing consult today and get the right unit for your needs