One of the most common questions homeowners ask when considering an air source heat pump is whether they can run out of hot water.

The simple answer is yes, it is possible to run out of stored hot water with a heat pump – just as it is with many conventional heating systems that use a hot water cylinder. However, with a correctly designed system and appropriately sized cylinder, it shouldn’t be something you experience regularly.

At Clear Skies Energy, we make sure your heat pump and hot water system are designed around the needs of your household, helping ensure you have plenty of hot water when you need it.

How Does a Heat Pump Provide Hot Water?

Unlike a combi boiler, which heats water almost instantly when you turn on a tap, most air source heat pump installations use a hot water cylinder.

The heat pump takes energy from the outside air and uses it to heat water stored inside the cylinder. This hot water is then available for showers, baths and hot taps throughout your home.

Once some of the stored hot water has been used, the system can heat the cylinder again.

This means the amount of immediately available hot water depends largely on the capacity of your cylinder and how much hot water your household uses.

So, Can the Hot Water Actually Run Out?

Yes. If you use the hot water in the cylinder faster than the heat pump can replenish it, you may temporarily run out.

For example, imagine several people taking long showers one after another, while somebody else runs a bath. A smaller hot water cylinder could eventually become depleted.

The important word here is temporarily.

Your heat pump hasn’t stopped working or run out of energy. It simply needs time to bring the water in the cylinder back up to temperature.

This is why choosing the correct cylinder size is so important.

How Quickly Does a Heat Pump Reheat a Hot Water Cylinder?

Heat pumps generally heat water more gradually than a traditional gas or oil boiler. This is part of the reason why good system design matters so much.

How long reheating takes depends on several factors, including:

• The size of your hot water cylinder
• The capacity and output of your heat pump
• The starting temperature of the water
• The target hot water temperature
• Outside air temperature
• How much hot water is being used while the cylinder is reheating

Rather than relying on rapid recovery from an undersized cylinder, a properly designed heat pump system should provide sufficient stored hot water for the normal demands of the household.

What Size Hot Water Cylinder Do I Need?

There isn’t a single cylinder size that’s suitable for every property.

A household with one or two occupants will have very different hot water requirements from a family of five where several showers might be used every morning.

When specifying a heat pump system, installers should consider factors such as the number of occupants, bathrooms, showers and baths, as well as typical patterns of hot water consumption.

Choosing the right cylinder isn’t simply about installing the largest one possible either. It should be appropriately sized for the property and its occupants.

What Happens If Everyone Wants a Shower at the Same Time?

This is where heat pump system design becomes particularly important.

If several people regularly shower within a short period – for example, a family getting ready for work and school in the morning – this should be taken into account when the system is designed.

With sufficient stored hot water, several consecutive showers shouldn’t present a problem.

However, unusually heavy demand can still exhaust the cylinder. A large bath followed by several long showers, for example, could consume considerably more hot water than the household normally uses.

Once the stored supply has been used, you’ll need to allow the system to recover.

Can I Use an Immersion Heater as Backup?

Many heat pump hot water cylinders incorporate an electric immersion heater.

An immersion heater can provide a useful backup method of heating water and may also form part of the system’s hot water or legionella control strategy.

However, an immersion heater uses direct electrical resistance heating, so it generally isn’t as efficient as allowing the heat pump itself to heat the water.

For normal everyday use, your system should ideally be designed so that you’re not continually relying on the immersion heater simply to meet your household’s hot water requirements.

Should I Keep My Hot Water On All Day?

Not necessarily.

Modern heat pump systems can be programmed so that the cylinder is heated at suitable times according to your household’s routine.

For example, you might schedule hot water production ahead of the morning shower period and again later in the day.

The best schedule will depend on how your household uses hot water, the size of the cylinder and your electricity tariff.

Rather than constantly changing settings, a well-configured system should be able to operate automatically around your requirements.

Are Heat Pumps Suitable for Homes With High Hot Water Demand?

Absolutely – provided the system is properly designed.

Heat pumps can provide heating and hot water for everything from smaller homes to larger family properties. The key is ensuring that the heat pump, cylinder and overall system have been selected according to the property’s actual requirements.

Problems can occur when a system is incorrectly sized or when the occupants’ hot water habits haven’t been properly considered.

That’s why a professional heat-loss calculation and system assessment are such important parts of a heat pump installation.

What If My Heat Pump Keeps Running Out of Hot Water?

If you already have a heat pump and regularly find yourself without enough hot water, it may be worth having the system checked.

Potential causes could include an undersized cylinder, unsuitable hot water schedules, incorrect temperature settings or a system that hasn’t been configured correctly for the way your household uses hot water.

Occasionally running out after unusually heavy usage isn’t necessarily a sign of a problem. Running out during normal daily use on a regular basis is something worth investigating.

Do You Get Enough Hot Water From an Air Source Heat Pump?

For a properly designed installation, an air source heat pump should be capable of providing plenty of hot water for normal household use.

The experience is slightly different from using a combi boiler because you’re working with stored hot water rather than unlimited instantaneous hot water. But once the system has been correctly sized and programmed, most of the process happens automatically in the background.

The important thing is getting the design right from the beginning.

Considering an Air Source Heat Pump?

At Clear Skies Energy, we design heat pump systems around the property and the people living in it.

From calculating your home’s heating requirements to selecting an appropriate heat pump and hot water cylinder, careful system design helps ensure your installation is efficient, comfortable and capable of meeting your everyday hot water needs.

If you’re considering switching to an air source heat pump and want to know what system would work for your property, contact Clear Skies Energy today to discuss your options.