Quick answer: A high-temperature heat pump can send water round your heating at around 70-75°C, which is close to what a gas boiler does. That means many older homes can keep their existing radiators. The catch is efficiency: the hotter the water, the harder the heat pump works, so you pay a little more to run it than you would at lower temperatures. Here at The Edinburgh Boiler Company we’re MCS-certified heat pump installers, fitting both high-temperature and standard models in older Scottish homes, so we know where each one earns its keep.
I get asked about high-temperature heat pumps almost every week, usually by someone standing in the hallway of a lovely old stone house in Edinburgh or Stirling, looking nervously at a row of cast-iron radiators they don’t want to lose. It’s a fair worry. Below I’ll explain how these units work, what the efficiency trade-off really looks like using manufacturers’ own published figures, and when I’d recommend one over a standard heat pump with a couple of bigger radiators.
What is a high-temperature heat pump?
A high-temperature heat pump is an air source heat pump that can heat water to around 70-75°C using the heat pump alone, without an electric immersion or backup heater doing the heavy lifting. A typical heat pump design aims for a flow temperature of 35-50°C, which usually means larger radiators or underfloor heating.
Older gas and oil boiler systems were often designed to run at 70°C or more. The radiators were sized for that heat, so if you drop the flow temperature to 45°C, some rooms may never get properly warm on a cold January night. A high-temperature model gets round that by producing water hot enough for those radiators to keep doing their job.
It’s still an air-to-water heat pump in every other way. It sits outside, takes heat from the air, and feeds your radiators and hot water cylinder. Most models can also run at low temperatures when the weather is mild, which is where they’re at their most efficient. If you’re new to all this, our guide to whether you need new radiators for a heat pump is a good place to start.
How does R290 (propane) refrigerant make high temperatures possible?
Most of the new high-temperature heat pumps use R290, which is propane. Its properties let the heat pump push water to higher temperatures without the efficiency falling off a cliff.
Here’s the simple version. Every refrigerant has a “critical temperature”, a point above which it stops behaving usefully for heating. According to CIBSE Journal, R32 (the refrigerant in many older-generation heat pumps) has a critical temperature of 78.1°C, while R290 sits much higher at 96.7°C. That extra headroom means an R290 heat pump can produce 70-75°C water while staying comfortably within its working range.
There are two other plus points:
- Low global warming potential. R290 has a GWP of around 3, compared with 675 for R32. If any refrigerant ever leaked, its climate impact would be tiny.
- Future-proofing. Manufacturers are moving their ranges over to natural refrigerants, so an R290 unit is in line with where the industry is heading.
Propane is flammable, so there are rules on where the outdoor unit can go and how far it must sit from doors, windows and drains. Many R290 heat pumps are monobloc units, with all the refrigerant sealed inside the outdoor box, which keeps things simple and safe. This is one reason it matters to use a properly trained, MCS-certified installer.
R290 isn’t the only route. Daikin’s Altherma 3 H HT, for example, uses R32 and Daikin says it can still deliver 70°C water at -15°C outside. But for new installs, most high-temperature units I fit now use R290.
How much efficiency do you lose at higher flow temperatures?
Based on manufacturers’ own figures, going from a 35°C flow to a 55°C flow cuts seasonal efficiency by roughly a quarter. Push it up to 70-75°C and you lose a bit more on top of that.
The standard way to compare heat pumps is SCOP (seasonal coefficient of performance). A SCOP of 4 means that, over a heating season, you get 4kWh of heat for every 1kWh of electricity. The official ErP test figures are published at two flow temperatures, 35°C and 55°C, so we can see the drop clearly.
| Model (size) | SCOP at 35°C | SCOP at 55°C | Drop |
|---|---|---|---|
| Ideal HP290 (8kW) | 5.07 | 3.82 | About 25% |
| Baxi HP60 (8kW) | 5.20 | 3.89 | About 25% |
| LG Therma V R290 Monobloc (12kW) | 5.45 | 3.97 | About 27% |
| Panasonic Aquarea L bi-bloc (7kW) | 4.96 | 3.62 | About 27% |
Sources: Ideal HP290 spec sheet, Baxi HP60 product page, LG product page, Panasonic Aquarea L series datasheet.
Manufacturers don’t publish ErP SCOP figures at 70-75°C, so I can’t give you a lab number for those temperatures. In practice, efficiency keeps falling as you go hotter. The good news is that a well-set-up heat pump only runs that hot on the coldest days. Weather compensation lowers the flow temperature when it’s milder outside, and on most days of a Scottish winter your system will be running well below its maximum.
To put the table into pounds, here’s a rough illustration. Say your home needs 12,000kWh of heat a year. Using the Baxi HP60 8kW figures and an electricity price of around 26p/kWh (roughly the Ofgem price cap rate for 1 October to 31 December 2026):
- At a SCOP of 5.20 (35°C flow): about 2,310kWh of electricity, or roughly £600 a year.
- At a SCOP of 3.89 (55°C flow): about 3,085kWh, or roughly £800 a year.
For comparison, a 90% efficient gas boiler would burn about 13,330kWh of gas for the same heat, around £1,070 at 8p/kWh. These numbers leave out standing charges and real homes vary a lot, but they show the shape of it: running hotter costs more, yet a well-installed unit can still compare well with gas. A good heat pump electricity tariff can tip things further in your favour.
Wondering which camp your house falls into? A room-by-room heat loss survey answers it quickly. Book a free heat pump survey and we’ll tell you honestly whether your radiators can stay.
When does a high-temperature heat pump make sense?
A high-temperature heat pump makes most sense when your home loses heat quickly and you can’t realistically change that, or when changing your radiators would be costly or disruptive. Here’s where I tend to recommend one:
- Stone-built homes and tenements. Solid stone walls are lovely, but many can’t easily take cavity insulation, and internal insulation eats into room sizes and cornicing. Common in Edinburgh, Musselburgh, Dalkeith, Perth and the Borders.
- Listed buildings and conservation areas. If you can’t add external insulation, change windows or swap period radiators, running hotter water may be the only practical option.
- Homes you’ve already insulated as far as you reasonably can. If the loft, floors and draughts are sorted and the walls are the limit, a high-temperature unit fills the gap.
- Homes where replacing radiators means lifting floors or redecorating every room. Sometimes keeping the existing system just saves a lot of hassle.
When a standard heat pump and a few bigger radiators is better
In a lot of homes, the smarter move is a standard heat pump running at 45-50°C, with two or three radiators upsized in the rooms that need it. That’s often true of 1960s to 1990s houses in places like Livingston, Bathgate, Dunfermline or Kirkcaldy, where cavity walls and lofts are already insulated.
Why? Because you’ll run at the efficient end of the table above every day of the year, not just on mild ones. Changing a handful of radiators usually costs a fraction of the running cost difference over the life of the system. A proper room-by-room heat loss survey tells us which way to go, and it’s also how we work out what size heat pump your house needs.
Many of the “high-temperature” units in the next section run just as happily at 35-45°C. So you’re not locked in. If you upgrade insulation or radiators later, you simply turn the flow temperature down and enjoy lower bills.
Which high-temperature heat pump is best?
There’s no single best high-temperature heat pump. The best one is the model that’s sized correctly for your home and set up properly. All of the units below can reach at least 70°C using the heat pump alone, according to each manufacturer. I’ve checked every maximum flow temperature against the manufacturer’s own literature.
| Brand and model | Refrigerant | Max flow temp (heat pump only) | Sizes |
|---|---|---|---|
| Daikin Altherma 4 H | R290 | 70-75°C | Several outputs, from 4kW |
| Vaillant aroTHERM plus | R290 | Up to 75°C | 3.5, 5, 7, 10, 12kW |
| Samsung EHS Mono R290 | R290 | 75°C (outdoor temperature -10°C and above) | 5kW to 16kW |
| Mitsubishi Ecodan R290 | R290 | Up to 75°C | 5, 6, 8.5, 10, 12kW |
| LG Therma V R290 Monobloc | R290 | Up to 75°C | 7kW to 16kW |
| Panasonic Aquarea L (bi-bloc) | R290 | 75°C (at -10°C outside) | 5, 7, 9kW |
| Baxi HP60 | R290 | Up to 75°C (at -10°C outside) | 4, 6, 8, 11, 13kW |
| Ideal HP290 | R290 | Up to 75°C | 4.5, 6, 8, 10, 12, 14kW |
| Worcester Bosch Compress 5800i AW | R290 | Up to 75°C | 4, 5, 7kW |
A few thoughts from fitting these across Scotland:
- Vaillant aroTHERM plus is very popular with installers and homeowners alike. It’s been around long enough that we know it well, and it handles high flow temperatures nicely.
- Mitsubishi Ecodan is another very popular name, and the R290 range covers most home sizes from 5kW to 12kW.
- Samsung is a strong all-rounder at a sensible price, and it’s a brand we install regularly.
- Ideal and Baxi are familiar boiler names, which some customers find reassuring, and both publish clear SCOP data.
- Daikin offers high-temperature options in both its R290 Altherma 4 H and its R32 Altherma 3 H HT ranges.
We’ve also looked at Viessmann’s range in our Viessmann heat pump review. Bear in mind that a top-rated heat pump fitted badly will always disappoint. Correct sizing, pipe sizes, controls and commissioning matter far more than the badge on the front.
How much does a high-temperature heat pump cost, and what grants are there?
Install costs for high-temperature models are broadly in line with other air-to-water heat pumps, and the overall job can work out cheaper if you’re keeping more of your existing radiators. The Energy Saving Trust puts the typical cost of installing an air source heat pump at around £14,000. That’s a typical figure only: your price depends on the size of the unit, the cylinder, any radiator or pipework changes, and the property itself. We give a fixed quote after a survey.
The really good news is that high-temperature heat pumps qualify for the same support as any other air-to-water heat pump in Scotland:
- Home Energy Scotland grant and loan. Up to £7,500 grant for an air-to-water heat pump, rising to £9,000 with the rural and island uplift, plus an optional interest-free loan of up to £7,500. The heat pump must provide all of your heating and hot water, so hybrids don’t qualify. You must get a written offer before work starts, and both the product and installer must be MCS certified. Our Home Energy Scotland grant and loan guide walks through the steps.
- Warm Homes Loan Scheme. The UK Government’s new scheme offers low and zero-interest loans of up to £20,000 for an air-to-water heat pump, with some loans running up to 30 years. It can be combined with Home Energy Scotland grants. We’re part of the scheme, so we can help you with it.
The Boiler Upgrade Scheme you may have read about only covers England and Wales, so it doesn’t apply to Scottish homes.
Whichever type suits you, we’ll handle the Home Energy Scotland grant paperwork and talk you through the Warm Homes Loan Scheme too. Book your free survey to get a fixed price for your home.
High-temperature heat pump FAQs
Can a high-temperature heat pump work with my existing radiators?
Often, yes. That’s the main reason to choose one. Because it can produce water at around 70-75°C, it can usually heat radiators that were sized for a boiler. We still check every room in the survey, as the odd radiator may need upsizing.
Are high-temperature heat pumps less efficient?
Yes, when they’re running hot. Manufacturer figures show SCOP falling by about a quarter between 35°C and 55°C flow, and it drops further at 70-75°C. Weather compensation keeps the flow temperature as low as possible, so most of the time they run well below their maximum.
Is R290 safe to have at my home?
Yes, when installed correctly. R290 is propane and is flammable, so manufacturers set rules on positioning and clearances. In monobloc units the refrigerant stays sealed in the outdoor unit. An MCS-certified installer will follow those rules.
What’s the best high temperature heat pump in the UK?
There isn’t one winner. The Vaillant aroTHERM plus, Mitsubishi Ecodan R290, Samsung EHS Mono R290, Daikin Altherma 4 H, Ideal HP290 and Baxi HP60 are all strong options. The right choice depends on your home’s heat loss, space outside and budget.
Will a high-temperature heat pump cost more to run than a gas boiler?
Not necessarily. Even at a 55°C flow, a SCOP of around 3.8-3.9 can work out cheaper than gas at current price cap rates, especially on a heat pump tariff. Your actual bills depend on your home, your settings and your tariff.
Do I qualify for the Home Energy Scotland grant with a high-temperature heat pump?
Yes, as long as it’s an MCS-certified air-to-water heat pump providing all of your heating and hot water, and you’re an owner-occupier applying for your main home. You must have a written offer before work begins.
Can I turn the temperature down later if I insulate?
Yes. Most high-temperature models run happily at 35-50°C. If you improve insulation or swap a few radiators later, we can lower the flow temperature and your running costs will drop.
Talk to an MCS-certified heat pump installer
“Most people I meet with older homes assume a heat pump simply won’t work for them. Very often it will. Sometimes that’s a high-temperature model and sometimes it’s a standard unit with a couple of bigger radiators. The survey tells us which, and we’ll always give you an honest answer.”
As one of Scotland’s leading MCS-certified heat pump installers, The Edinburgh Boiler Company fits high-temperature and standard heat pumps across Edinburgh, Musselburgh, Dalkeith, Penicuik, Livingston, Bathgate, Linlithgow, Falkirk, Stirling, Dunfermline, Kirkcaldy, Perth, Glasgow and the Borders. We’re part of the Warm Homes Loan Scheme and can help with your Home Energy Scotland application too. Find out more about our heat pump installations and book your free survey.
