What size water heater do I need?
Answer two quick questions and get the recommended size. No sign-up, no math.
For 3 people with a gas heater. Your busiest hour uses about 136 L of hot water, so look for a tank with a First Hour Rating (FHR) of at least that.
Estimate only — confirm against the unit's spec label and your local code.
How water heater sizing works
The size you need depends on how much hot water your home uses in its busiest hour — think back-to-back morning showers plus a dishwasher or laundry. The key number on a water heater's label is the First Hour Rating (FHR): how much it can deliver in one hour. Match the FHR to your busy-hour demand and you won't run cold.
Gas units reheat water much faster than electric ones, so a gas one can use a smaller tank for the same demand. Tankless (on-demand) water heaters are sized differently — by flow rate — and we'll add that calculator next.
Reference & education only — not professional advice. Confirm against the unit's spec label, your local code, and a licensed professional. Last reviewed 2026-06.