Safety boundary: Do not raise temperature settings to compensate for inadequate capacity without considering scald risk.
Peak demand
The key question is how much hot water the household needs during its busiest hour, not the daily average.
Storage systems
Tank volume and recovery rate work together. A smaller fast-recovery gas tank may behave differently from a larger electric tank.
Tankless systems
Capacity depends on flow and temperature rise. Canadian winter inlet water can be cold, reducing simultaneous flow at a given output.
Mixed-temperature use
Showers mix hot and cold water, so usable shower time is not equal to tank volume. Fixture flow rates and thermostat settings affect calculations.
Useful questions to record
- Is the problem at one fixture or throughout the home?
- Is there active leakage or relief-valve discharge?
- What fuel, capacity and age is the unit?
Related guides
Tank, Tankless and Heat-Pump Water HeatersA Canadian comparison of storage tanks, on-demand systems and heat-pump water heaters.No Hot Water or Inconsistent TemperatureSafe observations that distinguish whole-house, fixture and capacity problems.Water Heater Leaks and MoistureHow to identify the source area and protect the building without unsafe repairs.Water Heater MaintenanceA conservative maintenance plan for tanks and tankless units.