Interactive Calculator · 2026
Hot Water Demand Calculator
Plan your home's hot water at a whole-house level. Enter how many people live there, how much hot water each uses a day and how much of it lands in the peak morning rush — get your daily demand, the peak simultaneous draw and a suggested storage size.
Daily demand → peak simultaneous draw → suggested storage tank
Your household
Everyone who regularly uses hot water in the home.
Litres at usage temperature — a bucket bath is ~15–25 L, a shower ~20–35 L. Typical Indian homes sit around 15–25 L per person per day.
How much of the day's hot water is drawn in the concentrated morning rush — this drives the storage tank size so no one runs cold.
Daily demand vs peak draw vs storage
A storage geyser is sized around the peak draw; a solar system is sized around the daily litres.
Your home uses about 80 L of hot water a day, with roughly 48 L of it drawn together in the morning. For a storage electric geyser, plan around that peak draw — the next standard tank up is 50 L. A solar water heating system is instead sized near the full daily litres so its tank carries the whole day.
This is a whole-home planning estimate. A single bathroom's instant or storage geyser is sized separately — see the bathroom geyser-size calculator for that per-fixture number.
How this is calculated
- Daily hot water = occupants × litres per person = 4 × 20 = 80 L.
- Peak simultaneous = daily hot water × peak share = 80 × 60% = 48 L.
- Suggested storage = peak draw rounded up to the next standard tank [10, 15, 25, 50, 100, 150, 200 L] = 50 L for a storage electric geyser. A solar system is sized near the daily 80 L instead.
Indicative sizing for concept planning. Actual usage varies with bathing habits, inlet water temperature and set-point — confirm against manufacturer data before procurement.
Frequently asked questions
- How does the hot water demand calculator work?
- It works at a whole-home level in three steps. First it multiplies the number of occupants by the litres of hot water each person uses per day to get your daily hot water demand. It then applies the peak-morning share you set to find how much is drawn together in the morning rush. Finally it rounds that peak draw up to the next standard tank size to suggest a storage geyser capacity.
- What inputs do I need and what values should I use?
- You need three inputs: number of occupants, hot water per person per day and the peak-morning share. Count everyone who regularly bathes at home. For litres per person, typical Indian homes sit around 15 to 25 L per day, where a bucket bath is roughly 15 to 25 L and a shower 20 to 35 L. A peak share of about 50 to 70 percent suits most homes where mornings are busy.
- Should I size an electric geyser or a solar system differently?
- Yes. A storage electric geyser is sized around the peak simultaneous draw, so it only needs to hold the concentrated morning demand and reheats through the day. A solar water heating system is sized near the full daily litres because its tank should carry the whole day on one heating cycle. That is why the calculator shows both the peak draw and the daily total.
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