In 2022, Grant UK launched its combined volumiser/low loss header for installation with the Aerona air source heat pumps. In this blog, Neil Sawers, Commercial Technical Manager at Grant UK, explains the design of this unit and the role it has in heat pump installations.
Buffers, volumisers and low loss headers
It is well understood that installing an air source heat pump is not the same as installing a gas or oil boiler. Over the coming years, the number of heat pump installations is expected to continue to grow and the number of installers entering the market will also increase as the number of fossil fuelled appliance installs decline. Therefore, it is crucial for all heat pump installers to understand not just how to install, but why they should install a heat pump system in a specific way. Grant, like all manufacturers, need to equip installers with this knowledge and provide products to help achieve this success in the field.
Just as there are many types of system to consider (old or new, underfloor heating or traditional radiators, micro or mini bore pipe), there are many solutions available to the installer, each one with a different feature or benefit to assist the system operation. Some installers may prefer using a large 250 litre buffer, if they have the space (or a smaller 50 or 30 litre one if they don’t), some may prefer complete hydraulic separation by using a plate heat exchanger and some that see the benefits of a traditional low-loss header.
Why are low loss headers used in heat pump installations?
This leads me onto Grant’s combined volumiser/low loss header which was designed after analysing the most common issues our installers were experiencing in the field. There are many factors that can affect the performance of a heat pump, such as:
- incorrect flow rate
- high pressure drop in the pipe work or heat emitters
- lack of control to balance the flow rate in each zone.
Failure to address one or all of these could affect the performance of the heat pump and could be expensive to remedy after the event. While I am not discounting the benefits of utilising a buffer or plate heat exchanger (although the latter would still need a buffer on the heat pump side to provide the minimum water volume required for the heat pump) I have seen, at first hand, the benefits (not to mention the ease of installation) of using the Grant volumiser/low-loss header.
What is Grant’s low loss header?
The Grant combined volumiser/low loss header is larger than a standard low loss header because it holds 11.5 litres of system volume and accommodates a 3kW back-up heater. The unit, which is manufactured using 3mm mild steel, incorporates 50mm insulation. It is also supplied with a 16A relay, two 28mm isolating valves, a ½” drain cock, a ¼” manual air vent, a reducing bush and four blanking plugs. It has a white, powder coated case, designed to be wall mounted and installed internally and can be piped up to and from either side. The heater can be controlled by the heat pump, the system controls or by a separate air thermostat.
What does Grant’s low loss header do?
This unit has multiple functions but principally it serves as a volumiser and hydraulic separator as follows:
- it provides an extra 11.5 litres to the system volume connected to the heat pump
- it also gives hydraulic separation of the primary circuit of the heat pump from the secondary system circuit.
This means that the flow rate/differential through the heat pump can be maintained, irrespective of the flow rate/differential required on the system side. The size of the unit also helps to minimise the internal turbulence that can occur when the system mass flow of water exceeds that for the primary heat pump circuit. Furthermore, its factory-fitted 3kW electric immersion element provides a back-up/supplementary heat source if required.
You can download the electrical and hydraulic schematics for the Aerona Installation Packs - which incorporate this low loss header and volumiser – via our Technical Literature Downloads Hub.
What are the benefits of installing Grant’s low loss header?
The Grant combined volumiser/low loss header enables installers to separate the heat pump from the rest of the system and this is beneficial in many ways:
- First and foremost, the performance of the heat pump will be protected because the volumiser/low loss header is allowing the heat pump to maintain the target flow temperature while the system side can achieve whatever flow rate/differential is required to deliver the heat to the emitters.
- Secondly, the header can be used to pair two heat pumps together for larger systems or even a heat pump with an oil or gas boiler. Perfect for even larger systems where the heat pump could only be expected to satisfy a portion of the overall heat loss.
Additional resources
Hopefully I have provided an explanation here about what Grant’s combined volumiser/low loss header is and why we feel it has a place in a heat pump installation. As I have said already, it is not the only way to install a heat pump and there are experienced engineers who have their own methodologies which work extremely well too. The low loss header is just one way but hopefully it provides engineers with an installer-friendly solution to future-proof their heat pump installations.
- You can listen to Neil discussing this topic in further detail in Episode Three of the Net Zero Heating Show
- Follow the link here to read more about Grant’s heat pump installation kits which include the low loss header, as well as Grant’s range of internal and external volumisers.
This blog was originally published on 13th April 2022 and updated on 10th July 2025.
