Heat pumps
High Temperature Heat Pumps: Are They Still a Thing?
The label matters less than it used to. The temperature your heating needs still matters a lot.
Published
The term “high temperature heat pump” is becoming obsolete. With older generations, you had to choose a specific high-temperature model if you needed hotter water. Many of the new heat pumps I fit now have that capability as standard, so it no longer sets them apart as a specialist type of heat pump.
Every domestic R290 heat pump I am familiar with has high-temperature capability as standard, with models such as Vaillant aroTHERM plus and Mitsubishi Ecodan reaching up to 75°C. That does not mean we should design every heating system to run that hot. I spend a fair amount of time explaining that a heat pump can get the radiators hotter, then recommending that we don't.
The useful question is not just, “How hot can it go?” It is, “What temperature does this house need, and what will that cost to run?”
- Higher-temperature capability is useful. It gives us options for radiators and hot-water heating.
- It does not remove the benefit of lower temperatures. The heat pump generally uses less electricity when it has less of a temperature lift to make.
- Keeping every radiator is a choice to assess, not a promise. Sometimes a few changes are worth making; sometimes the existing radiators are already suitable.
- Compare the whole proposal. Installation cost, running cost, disruption and comfort all matter.
What is a high temperature heat pump?
It is a heat pump designed to supply hotter heating water than a lower-temperature model can provide. In domestic product descriptions, you will often see maximum flow temperatures around 70–75°C, although the exact limit depends on the equipment.
Flow temperature is the temperature of the water leaving the heat pump for the heating system. It is not the temperature of the room, and it is not automatically the temperature of the water stored in your cylinder.
| The figure | What it tells you |
|---|---|
| Maximum flow temperature | What the equipment can achieve within its specified operating conditions. |
| Design flow temperature | What the heating is designed to need at the local winter design temperature. |
| Day-to-day flow temperature | What it needs today. With weather compensation, this normally falls when the weather becomes milder. |
A unit with a 75°C maximum does not have to spend its life producing 75°C water. Equally, a maximum-temperature claim does not prove it can deliver your required heating output at that temperature on a very cold day. We need the performance information for the actual conditions.
Why the high-temperature label used to matter more
With earlier generations, the distinction was more useful. Many ordinary R410A and R32 systems had a lower practical temperature range, while specially designed high-temperature equipment offered a different way of replacing a boiler.
Some older systems used two refrigerant circuits to lift the temperature in stages. Other designs achieved higher temperatures with a specially developed compressor and refrigerant circuit. It was more than changing a setting.
| Example | Approach and advertised capability |
|---|---|
| Earlier Daikin Altherma Flex | A cascade arrangement using R410A and R134a circuits, supplying water up to 80°C. |
| Samsung EHS Mono HT Quiet | An R32 design with a purpose-designed compressor and flash injection, supplying water up to 70°C. |
| Modern R290 ranges | Examples such as Vaillant aroTHERM plus and Mitsubishi Ecodan R290 advertise flow temperatures up to 75°C. |
Manufacturer sources: Daikin's earlier Flex catalogue, Samsung HT Quiet, Vaillant aroTHERM plus and Mitsubishi Ecodan R290. These are maximum capabilities, not a like-for-like efficiency comparison.
So it would be wrong to say R32 could never do high temperatures. Some models specifically could. The change is that higher-temperature capability is now available across many familiar R290 products.
That is why I find the label less useful as a starting point. I would rather choose the right heat pump and heating design than assume an older house needs something with “high temperature” on the box. The useful checks are the model's maximum temperature and the output and efficiency it can deliver in the conditions we need.
Can a high temperature heat pump keep your existing radiators?
It can make that possible, but I would still assess every room. A radiator gives out more heat when the water inside it is hotter. That does not tell us whether the radiator needs hotter water, or whether it already has enough surface area to heat the room at a lower temperature.
We start with room-by-room heat loss and radiator output. Then we can compare keeping the system as it is with making a few useful changes. There is no point replacing a perfectly suitable radiator just because a heat pump is being installed.
There can be a good reason to change an undersized one, though. A larger radiator may allow the whole heating system to run cooler. Practical insulation and draught improvements can reduce the heat the house needs in the first place.
I would explore those options before accepting higher electricity use for the life of the installation. That is not a demand to rebuild or fully insulate the house before fitting a heat pump. It is a conversation about which improvements are possible and worth paying for.
High temperature heat pump running costs
Heating water to a higher temperature generally reduces heat-pump efficiency under otherwise comparable conditions. You can still have a warm house, but you may use more electricity to achieve it.
I would show the customer both sides: the extra installation cost of improving the radiators, and the estimated running costs of the alternatives. Spending more on the installation is not automatically the right answer, but neither is keeping every radiator at any ongoing cost.
| For the same 12000kWh of useful heat | Seasonal performance of 3 | Seasonal performance of 4 |
|---|---|---|
| Electricity required | 4000kWh | 3000kWh |
| Your cost at an assumed 25p/kWh | £1000 | £750 |
This explains the arithmetic, not a prediction for your house. The tariff is an assumption, not a current quote. These performance figures are not assigned to particular flow temperatures or models. A real comparison must include the expected heating and hot-water performance, controls and any backup-heater use.
The saving in that example is £250 a year. Whether a radiator alteration is worthwhile depends on its cost, the likely saving and how long you expect to keep the system. My heat-pump running costs guide goes into the other things that affect the bill.
One customer chose hotter water instead of radiator changes
I have deliberately taken that approach once for a customer with substantial solar generation who did not want the radiators changed. They understood the choice and preferred to keep the existing emitters.
That is not a recommendation for everyone with solar panels. Generation is lower in winter, when heating demand is highest, and using electricity at home can mean giving up export income. The customer's preference matters, but we should make the decision with realistic costs rather than assume solar means free heating all year.
Higher temperatures can be useful for hot water
When the system is set up for it, a high-temperature-capable heat pump can complete the Legionella cycle without needing an immersion heater. That is a genuine advantage of being able to produce hotter water. Vaillant identifies this capability for aroTHERM plus.
Using the heat pump for that cycle is much more efficient than using the immersion. An immersion turns one unit of electricity into roughly one unit of heat, whereas the heat pump can deliver more heat from the same electricity. Its efficiency falls at higher water temperatures, so the actual saving depends on the equipment and operating conditions.
Do not confuse a high flow-temperature setting with every part of the cylinder reaching the required treatment temperature. Cylinder design, sensors, time at temperature and the agreed hygiene controls all matter. The arrangement should follow the equipment instructions and a competent assessment of the household's risks, including vulnerable occupants.
This is not a reason to disable an agreed hygiene cycle or remove backup heating. My heat-pump hot-water guide covers the everyday cylinder side of the system.
Occasionally, I find heat pumps running hotter than they need to
One cause is fixed flow temperature. A setting that keeps the house warm on a cold day is left unchanged when the weather becomes mild. The system keeps sending out hotter water than the house needs.
Weather compensation adjusts that water temperature with the weather. We set it to provide enough heat on cold days, then reduce the temperature as the heat loss falls. The Energy Saving Trust explains why this helps efficiency and reduces cycling.
When I improve these settings, I see less starting and stopping, and customers report more consistent room temperatures. It is something to get right during commissioning, not an optional extra.
A high-temperature-capable heat pump can still use weather compensation. Buying that capability does not commit you to running it flat out all winter.
What I would ask before choosing one
- What is the house's calculated heat loss? Not a guess from the number of bedrooms.
- What flow temperature is the design based on? Ask about the cold-weather design, not just the unit's maximum.
- Which radiator changes would actually help? Compare the cost and disruption with the expected running-cost benefit.
- What practical insulation improvements are available? Reducing heat loss may be a better investment than producing more heat.
- What output and efficiency can this model deliver in those conditions? Include any expected backup-heater use.
- Who will set up the controls? Weather compensation needs commissioning for your home.
The aim is a warm home with a sensible installation cost and an electricity bill you understand. A higher maximum temperature is one useful capability, not the whole design. Our heat-pump installation service starts with the building and heating requirements, then the equipment choice.
High temperature heat pumps: common questions
Are high temperature heat pumps still a separate category?
The term is still used, but the distinction is less useful now that many modern R290 ranges can produce hotter water as standard. Compare the actual model's output, efficiency and operating limits, rather than relying on the label.
Can R290 heat pumps run at high temperatures?
Yes. Every domestic R290 heat pump I am familiar with has high-temperature capability as standard. The exact maximum and available output depend on the model and outdoor conditions. That does not mean your heating needs to run at its maximum temperature.
Can I keep my radiators with a high temperature heat pump?
Possibly. We need to compare each room's heat loss with its radiator output at the proposed water temperature. Keeping them may be sensible, or a few changes may allow lower temperatures and lower running costs.
Is a heat pump that can reach 75 degrees C inefficient?
Not simply because it can reach that temperature. It can still run at lower temperatures. Asking it to produce hotter water generally reduces efficiency compared with cooler operation under otherwise comparable conditions.
Does an old house need a high temperature heat pump?
Not necessarily. The building's heat loss and the radiators' output determine the required water temperature. Assess the house and practical improvements rather than choosing a temperature from its age.
Do high temperature heat pumps cost more to install?
There is no useful fixed premium across the category. Many mainstream R290 products already have higher-temperature capability. Compare complete installations, including the cylinder, radiator work, controls and commissioning.
Planning a heat pump for an older home?
At Vector Heat, I help homeowners across Lincolnshire compare the heating design and practical building improvements together. We can look at what you have, what is worth changing, and what you would prefer to keep.
