Estimate a household’s daily hot water demand, the energy to heat it and a suggested storage size — a starting point for sizing a hot water changeover.
Indicative only. Real system selection depends on peak demand, recovery rate, storage vs continuous flow, energy source and delivery temperature (with tempering to 50 °C at fixtures). Follow AS/NZS 3500.4.
Quoting a hot water changeover? traqR turns your sizing into a quote, job and invoice with the unit on the job card.
Start free trialMultiplying the number of people by a typical daily hot water use per person gives the household’s daily hot water demand.
Heating that water from the cold inlet temperature to storage temperature takes energy — about 4.19 kJ per litre per °C — which converts to kWh per day.
Storage size (or a continuous-flow unit’s capacity) is chosen to meet daily and peak demand, then matched to the energy source and installation.
It depends on the number of people and their usage. A rough guide is 40–60 litres of hot water per person per day, so a four-person household needs around 160–250 litres of storage, or an equivalent continuous-flow unit. Peak demand and recovery rate also matter.
Heating water takes about 4.19 kJ per litre for every degree of temperature rise. Raising 200 litres from 15 °C to 60 °C uses roughly 10.5 kWh. It’s why hot water is one of the biggest energy users in a home, and why heat-pump and solar systems can save a lot.
Storing at 60 °C or above controls Legionella bacteria. To prevent scalding, the water is then tempered down to a maximum of 50 °C (45 °C in some care settings) at the fixtures, as required by the plumbing code.
Storage systems hold a reservoir of heated water and suit steady, predictable demand; continuous-flow (instantaneous) units heat on demand with no storage, suiting variable use and saving standby losses. The best choice depends on demand pattern, space, energy source and budget.
This calculator is an indicative aid. Hot water system selection depends on peak and daily demand, recovery, energy source, delivery temperature and tempering, and must comply with AS/NZS 3500.4 and be installed by a licensed plumber.
traqR turns your sizing into a quote, job and invoice with the unit on the job card. Try it free for 14 days.