Heat-pump advice
How long does a heat pump take to heat water?
A complete cylinder reheat may take roughly one to two hours, but that is not the wait most households experience. Day to day, the system usually replaces only the hot water that has been used.
The practical answer
Three different waits are often confused
When somebody asks how quickly a heat pump makes hot water, they may mean the time for water to reach the tap, the recovery after a shower, or a complete reheat from cold. Those are different situations.
Usually seconds
If the cylinder already contains hot water, the wait is mainly the time taken for water to travel through the pipework.
Normally a partial top-up
Cold water replaces the amount used. The heat pump reheats that portion; it does not usually start with a completely cold cylinder.
Often around 1–2 hours
This is the slowest and least typical case. Cylinder size, temperature rise, available output and coil performance all matter.
Illustrative recovery
Example full-reheat times
These examples show the underlying energy calculation, not a promise for a particular product. They assume the stated average heat is actually transferred into the cylinder throughout recovery.
| Cylinder volume | Temperature rise | Heat required | Average heat transferred | Illustrative time |
|---|---|---|---|---|
| 150 litres | 10°C to 50°C | About 7.0 kWh | 5 kW | About 1 hr 24 min |
| 200 litres | 10°C to 50°C | About 9.3 kWh | 6 kW | About 1 hr 33 min |
| 250 litres | 10°C to 50°C | About 11.6 kWh | 8 kW | About 1 hr 27 min |
| 300 litres | 10°C to 50°C | About 14.0 kWh | 10 kW | About 1 hr 24 min |
Try your figures
Simple cylinder reheat calculator
The calculator estimates a full reheat using the water volume, temperature rise and average heat transferred. Use it to understand the relationship—not to select equipment.
Why the real result can differ
- The heat pump may deliver less output at a high cylinder temperature or in colder weather.
- The cylinder coil must be able to transfer the available heat.
- Controls may pause space heating while hot water is prioritised.
- A legionella cycle may use an immersion heater to reach a higher temperature.
- Normal recovery usually begins before the whole cylinder is cold.
Good design
What Enerus checks before specifying a cylinder
- Number of occupants and usual shower or bath pattern
- Simultaneous demand from multiple bathrooms
- Available cylinder and maintenance space
- Heat-pump output at domestic-hot-water conditions
- Cylinder heat-exchanger area and recovery performance
- Incoming cold-water flow and pressure
- Tariff schedule, controls and occasional peak demand
- Future household changes—not bedroom count alone
Common mistake
Bigger is not automatically better
An oversized cylinder costs more, occupies more space and stores more water than the household may need. An oversized heat pump chosen simply to shorten hot-water recovery can cycle inefficiently during space heating.
The heat pump should be selected against the home’s calculated heat loss. The cylinder, coil and controls should then be designed to provide the required hot water as part of the same system.
Questions homeowners ask
Heat-pump hot-water FAQs
Will I run out of hot water with a heat pump?
A properly selected cylinder and recovery strategy should cover the household’s normal pattern. If shortages happen repeatedly, the cylinder volume, target temperature, schedule, sensor position, coil performance and household use should be reviewed.
Is a heat pump slower than a combi boiler?
They work differently. A combi heats water as it passes through the boiler and is limited by its flow rate. A heat-pump system normally prepares and stores hot water in advance. The more useful comparison is whether enough hot water is available when needed and what it costs to provide.
Does a higher cylinder temperature give me more hot water?
Yes. Hotter stored water mixes with more cold water at the outlet, increasing the usable quantity. It also takes more energy to reach the higher temperature and normally reduces heat-pump efficiency, so the best everyday target is the lowest setting that reliably meets demand.
Can hot water be made during cheaper tariff periods?
Often. A suitable controller can schedule recovery in off-peak periods. The schedule should still protect comfort, hygiene requirements and space-heating performance.
Can my existing cylinder be reused?
Sometimes, but it must be assessed. The installer needs to check its condition, volume, heat-exchanger performance, insulation, controls and compatibility with the proposed heat pump. A standard boiler cylinder may have an undersized coil for effective heat-pump recovery.
Designed around the household
Estimate the complete system—not just the outdoor unit
The Enerus estimator considers property heat loss, local design conditions, suitable heat pumps, cylinder options, running costs and available grant support. Final sizing follows survey and room-by-room design.