High temperature heat pumps explained
A plain-English guide to what makes a heat pump “high temperature”, what that costs in efficiency, where it is used and what to ask a supplier.
What “high temperature” actually means
A conventional commercial heat pump is designed around low-temperature heating: water leaving the unit at a temperature that suits well-insulated buildings, fan coils or underfloor circuits. A high temperature heat pump is a unit built (usually through the choice of refrigerant, compressor and cycle) to deliver noticeably hotter water, or in some industrial designs steam or hot air, from the same electrical input.
The phrase has no fixed definition in UK law or in the MCS standards, and manufacturers draw the line in different places. In practice it is used for three different things: units that serve older radiators that were sized for hot gas-boiler water; units that heat domestic hot water to storage temperatures; and industrial units that supply process heat. When you read a data sheet, ignore the label and look for two numbers: the maximum flow temperature the unit can deliver, and the rated SCOP at the flow temperature you actually need.
Why flow temperature trades against SCOP
A heat pump moves heat from a cold source (outside air, the ground, waste heat) up to the temperature you need. The bigger that temperature lift, the more work the compressor does for each unit of heat delivered, and the lower the coefficient of performance. That is why a lower flow temperature raises the seasonal figure (SCOP), and why the same machine will rate differently when quoted at a low and at a high flow temperature. The SCOP guide explains how the seasonal figure is rated.
The consequence for your decision is that the cheapest-to-run answer is usually the lowest flow temperature the building can live with. Running a high-temperature unit hard all winter only to avoid replacing emitters can cost more in electricity than the emitter upgrade would have cost to install. Running-cost break-even against gas depends on the SCOP you actually achieve; the running-cost calculator shows it with your own tariffs.
Where high temperature units are used
- Retrofit onto existing radiators. Where pipework and radiators were sized for hot boiler water and replacing them is disruptive, a higher-output unit can reduce the emitter work. The alternative is a hybrid design that keeps the boiler for the coldest days: see hybrid and boiler-replacement retrofit.
- Hot water. Heating a large hot-water load to storage temperature needs a different duty from space heating. Options include a dedicated high-temperature unit, a two-stage design, or a heat pump that pre-heats with a top-up from another source.
- Process heat. Food and drink, laundries, paper, chemicals and other industrial sites use heat at higher temperatures for washing, drying, pasteurising and similar tasks. The most favourable cases are usually those where waste heat from the process or from refrigeration can feed the heat pump. See industrial process heat pumps.
One published installer guide (Fuse Energy, updated 8 July 2026) gives a planning band of £150,000-500,000+ for high-temperature industrial systems. That is a secondary source and a planning range, not a quote; see the cost guide for how to read it.
Refrigerants: R290, R744 and R32 in general terms
The refrigerant is the working fluid inside the heat pump, and its properties limit how hot the unit can go and how it must be sited and handled.
| Refrigerant | What it is | Points to know |
|---|---|---|
| R290 | Propane, a natural refrigerant | Flammable (safety class A3). Needs attention to siting, ventilation and leak-release distances. Frequently used in newer units, including some that reach higher flow temperatures; this is the refrigerant behind many “r290 heat pump” searches. |
| R744 | Carbon dioxide, a natural refrigerant | Not flammable, but works at high pressure. Often discussed for hot-water and some high-temperature duties. |
| R32 | A hydrofluorocarbon (HFC) | Mildly flammable and a fluorinated gas, so F-gas rules apply to its handling. |
Flammability class and pressure are engineering and safety matters that the designer and installer must address under the relevant standards. They are not a reason to rule a refrigerant in or out on this page, but they are a reason to ask where the unit will sit and what clearances and leak-detection it needs. A flammable-refrigerant unit placed in a plant room or near an air intake raises different questions from one on an open roof.
The UK F-Gas Regulation and your supplier
Fluorinated gases are covered by UK F-gas regulation. GOV.UK says it is against the law to work with F gas without the correct qualifications, and that people who install, service, check for leaks in or decommission refrigeration, air-conditioning and heat pump (RACHP) systems need the appropriate certification. Operators of equipment above set refrigerant quantities also have leak-checking and record-keeping duties. The detail depends on the refrigerant, the charge and whether the unit is a sealed monobloc or a split system, so read the current guidance rather than relying on a summary (GOV.UK: qualifications required to work on equipment containing F gas).
This site is not an installer and holds no F-gas or other credential. The practical point is for you: ask any supplier for the certification of the people who will handle the refrigerant, and check credentials on the relevant public registers rather than relying on the quote.
What to ask a supplier
- What is the maximum flow temperature, and what is the rated SCOP at the flow temperature my building needs?
- What refrigerant does the unit use, what is its safety class, and what siting clearances and leak-detection does it need?
- What happens to output and efficiency on the coldest design day?
- Could a lower flow temperature, with some emitter upgrades or a hybrid boiler, give a better seasonal result?
- What controls, metering and commissioning are included, so I can check the SCOP once it is running?
- Who holds the F-gas certification for the work, and where can I check it?
Funding status
The Industrial Energy Transformation Fund (IETF), which supported some industrial heat projects, closed in July 2025 and has no successor. Its last application window shut on 19 April 2024. Do not plan a high-temperature project around it. Smaller sites under 45 kW thermal may be eligible for the Boiler Upgrade Scheme, and heating plant may attract capital allowances; the grants and funding guide sets out what is open and what has closed. Confirm tax treatment with your accountant.