Hot water replacement means removing an existing water heater and installing a new system that suits your home’s hot water […]
You are used to a comfortable hot shower, but suddenly the water turns cold. How long will you have to wait before it heats up again? It could be a few seconds or several hours, depending on the type of hot water system you have and how much hot water you have used.
A continuous-flow gas or electric system heats water as you use it, so there is no storage tank that needs to recover. A storage system takes longer because it has to heat the water that replaces what you have used.
As a rough guide, a 50-litre electric storage tank can take around 45–60 minutes to heat from cold, while a 250-litre tank can take around 2.5–3 hours. Gas storage is faster, with a 135-litre tank taking around 60–80 minutes and a 260-litre tank around 100–130 minutes. Heat pump systems usually take longer, with current 250–280 litre systems taking roughly 3–4.5 hours to heat a full tank, depending on the model.
Here’s a quick overview of how long different hot water systems typically take to heat or recover:
| Hot Water System | Typical Heating Time |
| Instantaneous gas | 5–15 seconds at the tap |
| Instantaneous electric | Almost immediate; a few seconds at the tap |
| Electric storage, 50 L | 45–60 minutes |
| Electric storage, 250 L | 2.5–3 hours |
| Gas storage, 135 L | 60–80 minutes |
| Gas storage, 260 L | 100–130 minutes |
| Heat pump, 250–280 L | About 3–4.5 hours |
| Solar hot water | About 3–5 hours in good sun |
Note: These are typical heating or recovery figures, not guarantees for every system. Your actual time depends on tank size, heating capacity, how much hot water you used, incoming water temperature and the system’s settings.
How Long Does an Electric Storage Tank Take to Heat Up?
An electric storage hot water system can take around 45 minutes to 5 hours to heat from cold, depending mainly on the tank size and heating element.
For example, typical figures published for Australian electric storage systems include:
| Tank Size | Typical Element | Initial Heat-Up |
| 50 L | 1,800 W | 45–60 minutes |
| 125 L | 2,400 W | 90–120 minutes |
| 160 L | 2,400 W | 2–2.5 hours |
| 250 L | 3,600 W | 2.5–3 hours |
| 315 L | 3,600 W | 3–4 hours |
| 400 L | 4,800 W | 4–5 hours |
These figures show why you cannot give one heating time for every electric hot water system. A 50-litre tank has far less water to heat than a 400-litre tank, while a higher-powered element can heat the same volume faster.
Rinnai’s technical data gives the heating capacity of electric elements more precisely. At a 50°C temperature rise, a 1.2 kW element heats about 20.6 litres per hour, a 2.4 kW element about 41.2 litres per hour, a 3.6 kW element about 61.9 litres per hour, and a 4.8 kW element about 82.5 litres per hour.
That gives you a simple way to understand the difference between systems.
More water + lower element power = longer heating time.
If you’ve just had several long showers and used most of the tank, you may need to wait for a substantial amount of cold replacement water to heat before the system has recovered fully.
How Long Does an Instantaneous Electric System Take?
An instantaneous electric system does not store a large volume of hot water. It heats water as it flows through the unit.
You can therefore get hot water within seconds rather than waiting for a tank to heat. There can still be a short delay at the tap because cold water already sitting in the pipe has to flow out first.
The main limitation is electrical capacity. The system needs enough power to heat the required flow rate, so the unit’s size, available electrical supply and number of outlets being used at once all matter.
How Long Does a Gas Storage System Take to Heat Up?
Gas storage systems generally recover faster than electric storage systems.
Typical figures for Australian gas storage systems are:
| Tank Size | Initial Heat-Up From Cold | Recovery After 50% Use |
| 90 L | 45–60 minutes | 15–25 minutes |
| 135 L | 60–80 minutes | 20–35 minutes |
| 170 L | 80–100 minutes | 30–40 minutes |
| 260 L | 100–130 minutes | 35–50 minutes |
| 360 L | 120–150 minutes | 45–65 minutes |
The difference comes from the heating capacity of the gas burner. A gas storage system can put considerably more heat into the water than a typical electric element, which is why recovery can be much faster.
How Long Does a Continuous-Flow Gas System Take?
Similar to an instantaneous electric system, a continuous-flow gas system does not store a large volume of hot water. It heats water as it passes through the unit.
Hot water can reach the tap in around 5–15 seconds. The short delay is usually caused by cold water already sitting in the pipe between the system and the tap.
Because there is no storage tank, you do not have to wait for a tank to heat up again after using hot water. The system’s capacity and flow rate matter instead, particularly when several showers or taps are running at the same time.
How Long Does a Heat Pump Hot Water System Take to Heat Up?
A heat pump hot water system generally takes around 3–5 hours to heat a full storage tank, although the exact time varies considerably between models.
Current Australian product data gives some useful examples:
| Heat Pump System | Tank Size | Published Heat-Up Time |
| Reclaim | 250 L | 3.08 hours |
| Sanden | 250 L | 3.61 hours |
| Quantum | 270 L | 3.71 hours |
| Rheem Ambiheat | 270 L | 3.5 hours |
| Rinnai Enviroflo | 250 L | 4 hours |
| Solarhart Atmos Eco | 280 L | 4.5 hours |
| Stiebel Eltron | 222 L | 5 hours |
Several published Australian heat pump data puts the typical full-tank heating time at 2–4 hours, with 1–2 hours for reheating after normal use and around 30–60 minutes when boost mode is available.
So why does a heat pump take longer?
It doesn’t heat water with a conventional electric element. Instead, it takes heat from the surrounding air and transfers that heat into the water. That process uses much less electricity, but it also means the tank heats more gradually.
The important thing is that you don’t normally need to wait 3–5 hours every time you take a shower. A correctly sized heat pump stores hot water in advance, so there should already be enough available for normal household use.
How Long Does Solar Hot Water Take to Heat?
Solar hot water can take around 3–5 hours in good sunlight to heat a full tank, although the actual time depends heavily on the amount of solar energy available.
On a clear sunny day, the collectors can provide most or all of the heat required. When sunlight is weaker, the system may need its gas or electric booster to finish heating the water.
That means your solar hot water system does not have one fixed recovery time.
For example:
- Good sunlight: around 3–5 hours for solar-only heating
- Cloudy or winter conditions: solar contribution falls and the booster supplies additional heat
- Gas booster: supplementary heating can take roughly 45–90 minutes
- Electric booster: supplementary heating can take around 1.5–3 hours
This is also why you might have plenty of hot water after a sunny day but find the supply lower after several days of poor weather.
If your system has a booster, that does not necessarily mean something has gone wrong. The booster is there to provide the extra heating when the solar collectors cannot provide enough energy.
What Makes a Hot Water System Heat Faster or Slower?
The heating time isn’t determined by the system type alone. Several things can change how quickly your hot water recovers.
# Tank Size
Tank size has a direct effect on heating time.
A 50-litre electric tank can take around 45–60 minutes to heat from cold, while a 400-litre tank can take around 4–5 hours with a typical heating setup.
The larger tank takes longer because there is much more water to heat.
However, the trade-off is that you have more hot water available before you run out. A larger household may therefore benefit from a larger tank even though its full heating time is longer.
# Heating Capacity
The heating element, burner or heat pump output also matters.
For electric storage systems, Rinnai’s figures show that a 1.2 kW element heats about 20.6 litres per hour, while a 4.8 kW element heats about 82.5 litres per hour at a 50°C temperature rise.
So two tanks with the same capacity can have very different recovery times if they use different heating elements.
The same principle applies to gas storage and heat pump systems. The tank size tells you how much water is stored, but the heating capacity tells you how quickly that water can be reheated.
# How Much Hot Water Did You Use
The amount of hot water you use affects how quickly your system can provide hot water again. The more hot water you use, the longer the recovery can take. For example, a short shower may only use part of the tank, so there is still hot water left for another use and less water for the system to reheat.
Conversely, a longer shower uses more of the stored supply, leaving more cold water to heat before the system fully recovers. This is why you should always know how much hot water your household typically uses when choosing the size of your system.
# Incoming Water Temperature
The water entering your tank isn’t the same temperature throughout the year. If the incoming water is colder, the system has to add more heat to reach its target temperature.
For example, heating water from 15°C to 60°C requires a larger temperature increase than heating it from 20°C to 60°C. That extra heat requirement can increase the recovery time, particularly for storage systems.
# Weather Conditions
Weather has the biggest effect on solar and heat pump systems. Solar hot water relies on sunlight, so cloudy weather reduces the amount of heat the collectors can provide.
On the other hand, heat pumps take heat from the surrounding air. The system can still operate in cooler weather, but ambient temperature affects its heating performance.
This is one reason published heat-pump heating times should be treated as model-specific figures rather than a guarantee for every installation.
# Your System Settings
Your system may not heat continuously.
For example, some electric storage systems operate on off-peak electricity, so the tank may heat during scheduled periods rather than immediately after you use hot water.
Heat pumps can also be programmed to heat at particular times.
Therefore, when you use most of your hot water during the day and your system is programmed to heat overnight, you may have to wait until its next heating period before the tank fully recovers.
For that reason, you should always check the timer and operating settings before assuming the system has a fault.
What Should You Do If Your Hot Water Isn’t Heating?
If your hot water is cold, work through these checks before calling for a repair:
- Check the power supply. For an electric system, check the switchboard to see whether the water heater’s circuit breaker has tripped. If the system has no power, it cannot heat the water.
- Check the gas supply. For a gas system, make sure the gas supply is on and the unit is operating normally. If the pilot light has gone out, follow the manufacturer’s instructions for relighting it.
- Check the settings. Look at the thermostat, timer, and operating mode. Some electric storage and heat pump systems heat during programmed periods, so a changed setting can stop the system from heating when you expect it to.
- Look for leaks. A leaking tank or connection can cause you to lose hot water. So, it’s worth looking for dripping water or pooling around the tank and pipes. If you find a leak, turn off the water supply and call a licensed plumber.
- Try the reset button. Some electric storage systems have a reset button on the thermostat. If the system has tripped, resetting it may restore heating. Follow the manufacturer’s instructions and don’t open the electrical components yourself.
- Check whether heating has become slower. If the system used to heat normally but now takes much longer, the problem could be a worn heating element, a faulty thermostat, a burner problem, or sediment buildup inside the tank.
If these checks don’t solve the problem and the water remains cold, have a licensed plumber or electrician inspect the system.
How Long Should You Wait Before Using Hot Water Again?
If you’ve used some of the hot water, wait for the system to recover before taking another long shower or bath. You may still have enough hot water for a shorter use while it reheats.
If you’ve used most of the tank and the water runs cold, check the system’s expected recovery time and wait for it to heat again.
If you regularly run out of hot water, don’t keep waiting. Your system may be too small for your household, so consider having its capacity and recovery rate checked.
The Bottom Line
The time your hot water system takes to heat depends on how it produces and stores hot water. Instantaneous systems heat water as you use it, while storage systems need time to reheat the tank after you use the stored supply. Heat pumps and solar systems work differently again, with heating affected by factors such as the weather, system settings and how much hot water you use.
If your system regularly runs out of hot water, takes longer than usual to heat, or no longer suits your household, E-Green Electrical’s experts can assess your situation, recommend a solution and help you pick and install the right system for your home.
