The short version

Roughly 50 litres of storage per person per day, plus a buffer. For most Hunter families:

  • 1 to 2 people: 125L (electric) or 135L (gas) or 200L (heat pump)
  • 3 to 4 people: 250L (electric) or 170L continuous-flow (gas) or 280L (heat pump)
  • 5 to 6 people: 315L (electric) or two 170L continuous-flow units (gas) or 315L (heat pump)

That is the rule of thumb. Real answer depends on a few things below.

Recovery rate matters as much as size

Recovery rate is how fast the unit reheats a tankful of cold water. A 250L tank that takes 4 hours to reheat is functionally different from a 250L tank that recovers in 90 minutes.

Gas units recover fast. Electric (especially off-peak) recovers slow. Heat pumps recover slow but they run on a quarter of the energy.

Off-peak electric: the catch

If you are on off-peak electric (cheap power overnight), your hot water heats up overnight and then you have to last all day on that one tankful. You need a bigger tank to cover that. That is why off-peak units are usually 315L for a family.

If you are on continuous tariff, you can use a smaller tank because it reheats during the day.

Gas continuous flow vs gas storage

Continuous flow (often called "instantaneous") gas units do not store water. They heat it as you draw it. You will literally never run out. The trade-off is they cost more upfront and need a bigger gas line if you plan to run two showers simultaneously.

Storage gas is cheaper to install and fine for most households. You can run out if you all shower back to back.

Heat pumps: the real maths

A heat pump is the cheapest hot water to run in the Hunter climate. Roughly a quarter of the running cost of an off-peak electric tank.

Two things to know:

  • Upfront cost is $3,800 to $4,800 supplied and installed, more than double a basic electric. Government rebates can knock $1,000 to $1,500 off this.
  • They are louder than a tank (the compressor whirs, like an air conditioner). Position matters. Not against a bedroom wall.

How I work it out for customers

Three questions:

  1. How many people in the house, and how do you shower (long, short, daily, weekly)?
  2. What do you currently have, and is anyone ever cold by the end of the shower?
  3. What is your power and gas situation, and do you have solar?

From there, real recommendation. Not a sales pitch, just what makes sense.

Get a personal estimate

The hot water sizing tool runs the same maths I use. Tells you a recommended capacity and ballpark running cost.

Open the sizing tool →