Before we delve into this topic it would be useful to quantify the meaning of domestic hot water.

Domestic hot water or DHW is frequently considered as hot water used solely for domestic properties and or dwellings. This is not the case, and its term refers to water used for domestic purposes such as showers, sinks, bathing, and general ablutions. So DHW heating means the Hot Water used in both domestic and commercial premises.

As climate change is high on the international policy agenda with the laser focus on reducing CO2 emissions. The heating sector is seen as a critical area to help reduce CO2, this is leading to many questions surrounding new technologies and applications for DHW heating. Therefore, within this blog we address the frequently asked question that is “Can Commercial Heat Pumps be used for domestic hot water?”

Domestic hot water and building Energy.

The energy a building requires for heating can be reduced by best practice design principles for example ensuring that the building is as thermally efficient as possible will result in the structure requiring less energy for heating services. This however isn’t the case with DHW heating as the demand is likely to remain constant.    

Currently, in both domestic and commercial premises the DHW services are most likely supplied via a gas fired appliance. Whether that be a Combi Boiler, Continuous Flow Water Heater, Gas Fired Storage Water Heater, or System Boiler with Cylinder.

One of the biggest problems faced with DHW production is that it can be susceptible to bacteria growth that is naturally occurring within the water supplies. These bacteria can grow if the DHW is not produced or stored correctly.

The easiest methods to combat or reduce this growth is to reduce storage or use appliances that achieve temperatures within the system above 60˚ C including areas that require stored hot water.

For these instances bacteria will either not have the time to grow or removed rapidly by the elevated temperatures. This is one of the plus factors for gas appliances as they can achieve elevated temperatures quickly or use technology to allow them to operate on demand with temperature accuracy.

At this moment in time gas appliances use fossil fuels as their energy source so until environmentally friendly gases such as Hydrogen and rDME become more readily available, Heat Pumps can play a key role in the decarbonisation of this sector.

So, can Heat Pumps be used for DHW production?

In short, the answer is yes, heat pumps can be used for DHW production. Whether they be air source heat pumps, commercial heat pumps or ground source heat pumps.

Because they can:

  1. Produce heat which can be transferred into the water in a similar fashion as a System Boiler would with an indirect Cylinder.


  1. Temperature - Heat Pumps will require a cylinder to transfer and store heat. Due to the required storage, we would need to consider temperature management because of the bacteria within the water.
  2. Legionella - ACOP L8 as well as Building Regulations require stored water to be kept at 60˚ C which is a temperature that can reduce Legionella proliferation.
  3. Heat Pump performance - The most common Heat Pumps currently on the market can produce hot water up to 60-63˚ C. There are elevated temperature heat pumps available that can generate water temperatures at above 70˚ C, but these are not as common just yet.
  4. Hot water - The Legionella bacteria would be killed off at 55˚ C it just takes longer so we could say that Heat Pumps producing 55˚ C water are perfectly safe doing so. There are also other measures we can take into consideration with the system design to further reduce any sort of risk for Legionella bacterial growth.
  5. Oversizing - Such measures are to avoid oversizing on the storage and to make sure the volume of water held within the system is used at least once or twice per day. For Heat Pumps with a maximum limit of 55˚ C we could look at including immersions within the cylinder. These immersions could be programmed to come on daily during quiet periods and heat the water up to 60˚ C or above, thus killing of the bacteria. This process would be classed as a pasteurisation cycle.

These measures mentioned are not unfamiliar to the HVAC sector, they are requirements when designing any DHW system whether that be Gas fired or Electric, so the transition from one to the other could only require a minor adjustment.

So, in conclusion, Heat pumps are more than capable of supplying domestic hot water. System designers must be considerate of the design considerations and performance requirements mentioned above to ensure that the optimum system is deployed.

For more information and schematics on domestic hot water heat pump design, download our brochure today! (Please check the side bar) or visit our commerical heat pump page Commercial Heat Pump Technology :: Rinnai UK (

We recognise that air source heat pump design is not a straightforward task especially when designing commercial heat pump systems, so we aim to take the pain out of the process with our design support, capital expenditure, operational expenditure and carbon modelling for a free consultation with our heat pump experts contact us today on 0300 373 0660 or Help me choose a product :: Rinnai UK (

Useful resources:

Commercial Heat Pump Design Criteria - Courses | The CPD Certification Service (