Heating
What size water heater do you need (liters)?
Storage water heater size in liters from household size, hot-water habits and heater type (electric or heat pump), with standard tank sizes.
Quick answer
A storage water heater is sized in liters from how many people use it and their hot-water habits, not by adding up every shower. A useful rule of thumb: about 20 liters of base plus 24 liters per person for normal daily showers — so a family of four lands around 115 liters and a 120-liter tank fits. The reason it isn’t "50 liters × 4 people = 200" is that the tank reheats between uses: daily heating quietly refills it, so a well-sized 100-120 liter tank covers a typical family.
Recommended tank size
100 L
- Estimated need
- ~92 L
- Back-to-back showers it covers
- ~3
Related: planning the whole system? Compare heating fuel costs
These are honest hobby ranges, not a plumber’s spec. A storage tank reheats between uses, so you need far less than "liters per shower × people" — daily reheating does the rest. Heat pump water heaters are sized larger because they reheat slowly, but use about 3× less energy. For an instantaneous (tankless) heater the number that matters is flow (kW / liters per minute), not tank liters. Oversize by one step if you have a bathtub or teenagers; undersize and you get cold showers at peak hour.
How it works
Two choices change the number. Type: an electric storage heater is cheap to buy and sized as above, while a heat pump water heater is taken one size larger (it reheats slowly) but uses about three times less energy — worth it if you have space and use a lot of hot water. And habits: a bathtub or two teenagers taking long showers pushes you up a size. Undersize and you run out of hot water at the morning peak; oversizing by one step is cheap insurance, oversizing by three is just paying to heat water you never use.
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Frequently asked questions
What size water heater for a family of 4?+
For four people with normal daily showers, a 100-120 liter electric storage tank is the sweet spot. Drop to 80 liters if showers are short and water-saving; go to 150 liters if you have a bathtub in regular use or teenagers taking long showers. A heat pump version would be taken one size up (120-150 liters) because it reheats more slowly.
Electric storage or heat pump water heater?+
A plain electric tank is cheap to buy but the most expensive to run — it turns 1 kWh of electricity into 1 kWh of heat. A heat pump water heater costs more up front and needs a ventilated space, but moves about 3 kWh of heat per kWh of electricity, cutting running costs roughly two-thirds. Rule of thumb: high hot-water use with space available → heat pump pays back; occasional use or a tight cupboard → simple electric tank.
How many showers does an 80-liter tank give?+
Roughly two back-to-back showers before it needs to reheat. A typical shower draws about 40 liters of hot water once mixed with cold, so 80 liters covers two people in a row; then the heater takes 1-2 hours to bring a full tank back to temperature. This is why sizing is about your peak hour, not the whole day — the tank refills itself the rest of the time.
Storage tank or instantaneous (tankless) heater?+
A storage tank keeps a reserve of hot water ready and is sized in liters; an instantaneous (tankless) heater makes hot water on demand and is sized in power (kW) and flow (liters per minute). Tankless never runs out and wastes nothing standing by, but needs a big electrical or gas supply to heat water fast, and can struggle to feed two taps at once. For a single bathroom with modest use it’s neat; for a family with simultaneous demand, a properly sized storage tank is usually simpler and cheaper.
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