Daikin Altherma vs Octopus Cosy: Which Air Source Heat Pump Is Better? (2026)
Quick Verdict
Daikin Altherma is the more efficient choice on its MCS-certified figures, with lower estimated running costs, while Octopus Cosy has the longer standard warranty (8 yr).
Side-by-Side Comparison
| Feature | Daikin Altherma | Octopus Cosy |
|---|---|---|
| Installed price (before grant) | £7,000 - £14,000Lower | £8,000 - £12,000 |
| After £7,500 grant (illustrative, England and Wales) | £0 - £6,500 | £500 - £4,500 |
| SCOP at 35°C (MCS) | 4.47Higher | 4.36 |
| SCOP at 55°C (MCS) | 3.54Higher | 3.43 |
| Largest size | 14kWLarger homes | 9kW |
| Standard warranty | 2 years | 8 yearsLonger |
| Longest warranty (conditions apply) | 7 years | 8 yearsLonger |
| Sound power (declared) | 54 dB(A)Lower | 56 dB(A) |
| Annual running cost (est., 45°C flow) | ~£655/yrLower | ~£675/yr |
| Refrigerant and max flow | R32, up to 70°C flow | R290, up to 70°C flow |
| Country | Japan | UK |
| UK brand | No | Yes |
| Best for | Buyers wanting a split system with a small outdoor unit, or 70°C flow for radiators (3 H HT) | Price-led switchers happy to buy and install through Octopus |
Specifications and pricing are indicative for the UK market as at June 2026. Post-grant figures illustrate the £7,500 Boiler Upgrade Scheme in England and Wales (Scotland uses the Home Energy Scotland grant and loan; Northern Ireland has no equivalent). Running costs assume ~10,000 kWh of heat a year at 26.32p/kWh (Ofgem cap average, October to December 2026; changes quarterly). Confirm current models and exact pricing with your MCS-certified installer.
Model by Model, Size for Size
Each Daikin Altherma model against the nearest Octopus Cosy size. Better figure in green.
| 8 kW vs 9 kW | Altherma 3 R 8kWR32 · ERGA08EAV3A | Cosy 9R290 |
|---|---|---|
| SCOP at 35°C (MCS) | 4.36 | 4.36 |
| SCOP at 55°C (MCS) | 3.24 | 3.43 |
| Sound power (declared) | 62 dB(A) | 56 dB(A) |
| Maximum flow temperature | 65°C | 70°C |
| Running cost (est.) | ~£695/yr | ~£675/yr |
| Installed price from (before grant) | £7,000 | £9,000 |
| Outdoor unit weight | 58.5 kg | 125 kg |
| Suits | 3-4 bed homes | 3-4 bed homes |
Sizes are the makers' labels; where a label is not the rated output, the brand page says what is. Prices are PumpSwap's indicative estimates. Running costs use the same basis as the table above.
Price Comparison
Daikin Altherma starts from £7,000 installed before any support (indicative, June 2026), while Octopus Cosy starts from £8,000. That is a difference of roughly £1,000 at the entry level. Daikin Altherma is the more budget-friendly option upfront, though Octopus Cosy may claw some of that back through running costs over time. Both are installed prices in GBP with 0% VAT (until 31 March 2027) already applied. In England and Wales the £7,500 Boiler Upgrade Scheme grant comes off both equally, so the pre-grant difference carries straight through: illustratively £0 - £6,500 for Daikin Altherma and £500 - £4,500 for Octopus Cosy out of pocket. Your MCS-certified installer claims the grant for you.
Efficiency Comparison
SCOP (seasonal coefficient of performance) is the key efficiency measure for a heating heat pump: the kilowatt-hours of heat you get per kilowatt-hour of electricity across a whole heating season. The figures here are MCS-certified, at 35°C flow (underfloor heating or large radiators) and 55°C (hotter radiators). Daikin Altherma is certified at 4.47 at 35°C and 3.54 at 55°C, while Octopus Cosy is certified at 4.36 and 3.43. On our estimates at a 45°C design flow temperature, the Daikin Altherma costs about £20 a year less to run at Ofgem cap electricity prices, or approximately £200 over ten years. Real-world efficiency depends heavily on system design and flow temperature, which is what the MCS heat loss survey is for.
Warranty Comparison
Daikin Altherma: 2 years as standard; 5 years free once Daikin's Stand By Me cover is activated, with annual maintenance; 7 years (years 6 and 7 paid) through partner installers. Octopus Cosy: 8-year manufacturer warranty on the hardware as standard, plus 2 years on workmanship. Cosy Care (paid, from £12 a month) extends cover on Octopus installs. On standard terms, the Octopus Cosy has the longer cover; the longer terms on either side depend on registration, servicing and the installer. Workmanship cover for the installation itself comes separately from your installer and should be in writing.
Noise Comparison
Noise matters in UK homes because the outdoor unit often sits close to a neighbour's boundary or a bedroom window. The like-for-like figure is the maker's declared sound power: the noise the unit itself emits. Daikin Altherma: 54 dB(A). Octopus Cosy: 56 dB(A). On paper the Daikin Altherma is quieter by 2 dB(A). What a neighbour hears is much lower and falls with distance, and permitted development rules require the installation to meet the MCS noise standard at their window, so siting matters as much as the unit.
Cold-Weather and Retrofit Suitability
Two things decide how well a unit suits an older UK home: cold-weather output and flow temperature. Daikin Altherma uses R32 refrigerant (up to 70°C flow), while Octopus Cosy uses R290 (up to 70°C flow). Both reach 70°C or more, so both can work with existing radiators; the decision comes down to price, warranty and installer availability. Modern units hold useful output well below freezing. In the colder parts of the UK (Scotland and northern England in particular), frosty mornings trigger short defrost cycles that trim efficiency, so ask each installer for low-temperature output figures and take the MCS heat loss survey seriously; radiator upsizing is more commonly recommended there so the system can run at efficient flow temperatures.
Pros and Cons
Daikin Altherma
Pros
- Split design with a compact outdoor unit (58.5 kg for the 3 R 8kW)
- Altherma 3 H HT reaches 70°C flow for radiator systems
- Rated to work down to -25°C (3 R) and -28°C (3 H HT)
Cons
- Standard warranty is 2 years; 5 needs Stand By Me activation and annual maintenance
- The 3 R 8kW has a high sound power (62 dB(A)), so siting matters
Octopus Cosy
Pros
- Octopus median quote £4,064 after the grant (June to September 2026)
- Designed and built in the UK
- 8-year hardware warranty as standard
- Your installer handles the grant paperwork
Cons
- Only available through Octopus or its accredited installers
- Newer hardware: Cosy 6 launched in late 2023, Cosy 9 in 2025
Which Should You Choose?
Choose Daikin Altherma if...
- You want a lower upfront cost (from £7,000 vs £8,000 before the grant)
- You want the higher certified efficiency (SCOP 4.47 vs 4.36 at 35°C, MCS)
- A lower declared sound power matters to you (54 vs 56 dB(A))
- You want lower estimated annual running costs (~£655/yr vs ~£675/yr)
Choose Octopus Cosy if...
- You want a longer standard warranty (8 yr vs 2 yr (up to 7))
- You want a UK brand with local manufacturing or headquarters behind it
- You want natural R290 refrigerant
The grant is the same, whichever brand you pick
Every air-to-water unit on this page qualifies for the £7,500 Boiler Upgrade Scheme grant in England and Wales (£9,000 for oil and LPG heated homes until March 2027) when fitted by an MCS-certified installer, who claims it on your behalf so it comes straight off the quote. Scotland uses the Home Energy Scotland grant of up to £7,500 (£9,000 rural and island) plus an optional interest-free loan; Northern Ireland currently has no equivalent scheme. 0% VAT on residential installations applies UK-wide until 31 March 2027. Accurate as at July 2026.
Heat pump guides
- Air source heat pump installation cost in the UK
- The best air source heat pumps in the UK, compared
- The £7,500 Boiler Upgrade Scheme, explained
- Air source heat pumps: costs, grants and brands
- Heat pump grants in London
- Heat pump grants in South East England
- Heat pump grants in South West England
- Heat pump grants in East of England
- Heat pump grants in East Midlands
- Heat pump grants in West Midlands
- Heat pump grants in Yorkshire and the Humber
- Heat pump grants in North West England
- Heat pump grants in North East England
- Heat pump grants in Scotland
- Heat pump grants in Wales
- Heat pump grants in Northern Ireland
Where are you?
See indicative costs and local installers for your area