For most homes, 200 to 220 litres suits 2 to 4 people and 300 litres suits 4 to 6. Go up a size for long showers, a big bath or teenagers. If you get regular hard frosts, choose a cold-climate model as well.
Start with the people
The number of people who shower in the house most days is the best single guide. As a general rule:
| People | Size | Stiebel Eltron models |
|---|---|---|
| 1 to 2 | 200 to 220 litres | SHP-O 200 Plus, SHP-O 201 Premium, WWK 222 H |
| 3 to 4 | 200 to 220 litres, or 300 for heavy use | SHP-O 200 Plus, WWK 222 H; SHP-O 300 Plus for heavy use |
| 5 to 6 | 300 litres | SHP-O 300 Plus, SHP-O 301 Premium, WWK 302 H |
Then look at how you use hot water
A heat pump reheats its tank more slowly than a big electric element, because it gathers heat from the air instead of forcing it in. So what matters is the biggest draw in one go, usually the morning showers.
- Long showers, a big bath or teenagers: go up a size.
- Two bathrooms used at the same time in the morning: go up a size.
- Washing machine and dishwasher on cold: you can stay at the smaller size.
The WWK H models and the SHP-O range have a backup element that helps when the household draws a lot at once, but it uses full-price electricity. Sizing right keeps it switched off.
Litres in the tank, litres at the tap
The tank stores water at around 60°C or more. At the shower you mix it with cold water to about 40°C, so you get more litres out than the tank holds. Stiebel Eltron rates the WWK 302 H at 540 litres of 40°C water from its 302 litre tank, and the WWK 222 H at 360 litres from 220.
Your winters decide Plus or Premium
The SHP-O Plus models and the WWK keep heating with the heat pump down to -5°C outside. The SHP-O Premium models have active defrost and keep running down to -10°C. In Canberra, Tasmania, alpine areas and the cold inland, choose a Premium.
There is a rebate reason too: in STC zone 5 (Canberra, Tasmania and colder parts of Victoria) the SHP-O 200 Plus earns no STCs, while the SHP-O 201 Premium earns 15. See rebates.
Check it fits the space
| Model | Height | Diameter | Weight full |
|---|---|---|---|
| SHP-O 200 Plus / 201 Premium | 1,478 mm | 650 mm | 304 kg |
| WWK 222 H | 1,553-1,569 mm | 690 mm | 340 kg |
| SHP-O 300 Plus / 301 Premium | 1,903 mm | 650 mm | 422 kg |
| WWK 302 H | 1,921-1,937 mm | 690 mm | 437 kg |
Outdoors, the SHP-O needs 500 mm clear either side of its air grille. Indoors, every model needs a room of at least 13 cubic metres, which will cool a few degrees while the unit runs. A full 300 litre unit weighs over 400 kg, so it needs a solid, level base.
Seven or more people
The largest single units here hold about 300 litres. A big household is usually better served by two units, or by a heat pump with a larger cylinder, sized by a plumber or hydronic designer from how the house actually uses water.