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Two numbers determine whether a hot water system will meet your needs: how much water the tank stores, and how fast it reheats once you start using it. Here's what you need to know.
When comparing hot water systems, most people focus on price or brand. The numbers that actually determine day-to-day performance are simpler than that: tank capacity and recovery rate.
Tank capacity tells you how much hot water is available before the system needs to reheat. Recovery rate tells you how quickly it can replenish that supply once it's been used. A system that excels at one but not the other can still let you down at the wrong moment.
The volume of hot water stored and immediately available. A larger tank means more hot water before the system needs to catch up — but only useful if the recovery rate can keep pace with demand.
Measured in litres per hour, this is how fast the system reheats water after use. In high-demand situations — multiple showers back to back — recovery rate is the number that decides whether you run out.
Not all heat pumps perform the same way, and the differences are significant enough to affect real-world comfort. Here's how the three most common options compare across the metrics that matter.
Smaller tank but very fast recovery. Can handle multiple consecutive showers without dropping in performance. Unaffected by outdoor temperature.
Bigger tank but slow recovery. Works well for households with spread-out usage. Struggles when multiple people shower in quick succession, particularly in winter.
Larger tank combined with significantly better recovery rate. The best balance of storage and reheat speed available in a heat pump — suitable for larger households and higher-demand settings.
Recovery rate — measured in litres of hot water reheated per hour — is the single most important number for any household with back-to-back demand. The gap between systems is significant.
Recovery rate (litres per hour) under normal operating conditions. Cold weather reduces heat pump figures further. Gas performance is unaffected by ambient temperature.
Heat pumps work by extracting heat from the surrounding air. This is what makes them efficient — they move heat rather than generate it directly. But it also means their performance is directly tied to outdoor air temperature.
When the weather is warm, heat pumps perform well and the recovery rates shown above are achievable. When it's cold — particularly overnight or during a Victorian winter — recovery rate drops. The figures in the chart above represent normal conditions; real-world cold weather performance will be lower for heat pumps.
Gas systems perform at the same recovery rate regardless of outdoor temperature. A winter morning performs identically to a summer afternoon. There is no seasonal variation in reheat speed.
Heat pump recovery rate falls as outdoor temperatures drop. Cold overnight or winter conditions reduce efficiency and extend reheat times — a factor that must be considered when sizing a heat pump for your household's actual usage pattern.
The right system depends entirely on how your household actually uses hot water. The same product can be perfectly adequate in one situation and completely unsuitable in another — the difference is whether demand is spread out or concentrated.
In a typical home, hot water usage is naturally spread across the day. One or two showers in the morning, dishes at lunch, a bath in the evening. A standard heat pump can work well here because there's recovery time built into the day's rhythm. Slow reheat rates are rarely noticed when demand is distributed.
In any setting where multiple people use hot water back-to-back — larger families, shared accommodation, households with structured morning routines — recovery rate becomes critical. If the system can't keep pace with consecutive demand, later users get lukewarm or cold water. Tank size alone cannot solve this if the reheat rate is too slow.
Three principles should guide any hot water system decision. Get these right and the system will work. Overlook any one of them and you risk an expensive mistake.
A bigger tank helps, but if the recovery rate is too slow, the tank will empty faster than it refills during any period of concentrated demand. Both numbers matter equally.
Heat pumps pull heat from the air. Cold overnight or winter temperatures reduce recovery rates further — a variable that gas systems simply don't carry. Factor in your climate and your morning usage pattern.
The 400L Reclaim CO₂ heat pump offers the best balance of storage and recovery for households with higher or more concentrated demand. Gas remains the fastest and most consistent option regardless of conditions.