Choose a hot water system for your busiest period of use and the time it has to reheat. A 250L tank may suit your household, but shower flow and timing can change the answer. When arranging hot water installation in Canberra, give the installer your shower routine as well as the number of people at home.
Updated 18 October 2026.
Measure demand before choosing 250L or 315L
To estimate shower flow, time how long it takes to fill a container of known volume at a safely accessible outlet. At 9 litres per minute, an eight-minute shower uses 72 litres of mixed water. Four such showers use 288 litres; at 12 litres per minute they use 384 litres. Those are outlet volumes, not litres drawn entirely from the hot tank. Include baths, visitors and other hot-water use in the busiest period.
How much shower water can a 250L tank provide?
For an idealised mixing example, a 250L tank at 60°C with 10°C incoming water can theoretically deliver 250 × (60−10)/(40−10) = 417L at 40°C. With 20°C inlet water, the same calculation gives 500L. The inlet temperatures are assumptions for the example, not measured Canberra averages. Stratification, pipe losses, thermostat operation and recovery change actual delivery. Use the manufacturer’s usable delivery and recovery figures when choosing the unit.
In that 417L example, dividing by 72L per shower gives about 5.8 eight-minute showers at 9L/min. Treat that as a theoretical mixing calculation. Usable storage, pipe losses, reheating and other outlets change what a real installation delivers. Leave temperature adjustments to the installer.
Check capacity and reheating together
Ask the installer to state the peak demand assumption, available reheating hours and recovery rate. A 315L tank stores 26% more nominal water than 250L, but the extra capacity does not tell you how quickly it reheats. YourHome discusses household demand and controlled-load limitations. If you often run out just before reheating becomes available, a tariff or scheduling issue may matter as much as tank size. Heat-pump storage also needs its own recovery assessment; do not transfer electric-element assumptions to a different technology.
Why winter changes the result
Colder inlet water needs a larger proportion of hot water to achieve the same shower temperature. That reduces the mixed-water volume available from a given amount of stored hot water. Simultaneous demand and recovery can change the outcome further.
Ask the installer to assess the unit for local conditions and the manufacturer’s delivery guidance. A calculation based on warm inlet water may overstate what the system can deliver on a cold morning.
250L versus 315L: capacity is only one factor
Compare useful delivery, recovery and the heating schedule, as well as physical dimensions and price. A larger tank needs space and may store more hot water than the household uses. A smaller tank may struggle during a concentrated morning peak.
Ask whether the proposed capacity still works if one more person moves in or the household’s shower routine changes. Avoid blanket rules such as automatically adding a fixed percentage for every off-peak installation.
Off-peak and controlled-load arrangements
Find out when your actual tariff permits heating and whether the system has a boost arrangement. Do not assume every controlled-load service runs for the same hours. If the tank cannot reheat during the busiest period, stored capacity needs closer attention.
Give the installer your tariff information and typical use times. A tariff change, timer setting or diagnosed fault may sometimes explain poor delivery better than tank size.
Continuous-flow systems are sized differently
For continuous flow, focus on the outlets that run together and the temperature rise the system must deliver. A litres-per-minute label is not a promise of the same flow under every inlet temperature. Read continuous-flow sizing for Canberra for the questions to ask.
Before choosing a replacement
Send the installer your existing label, available space, tariff details and busiest-period usage. Compare system types before assuming a larger electric tank is the only option. For hot water system installation in Canberra, call Ethan on 0423 491 249 and ask for a capacity assessment.