Octopus Cosy vs Grant Aerona3: Which Air Source Heat Pump Is Better? (2026)
Quick Verdict
Octopus Cosy is the more efficient choice with a higher SCOP, meaning lower running costs over time, while Grant Aerona3 is more budget-friendly with pre-grant pricing from £8,000 (the £7,500 grant applies equally to both in England and Wales).
Side-by-Side Comparison
| Feature | Octopus Cosy | Grant Aerona3 |
|---|---|---|
| Installed price (before grant) | £8,000 - £12,000 | £8,000 - £13,000 |
| After £7,500 grant (illustrative, England and Wales) | £500 - £4,500 | £500 - £5,500 |
| SCOP (seasonal efficiency) | 4.1Higher | 4 |
| Max heat output | 9kW | 10kWLarger homes |
| Unit warranty | 5 years | 5 years |
| Compressor warranty | 5 years | 5 years |
| Noise level | 45dBQuieter | 47dB |
| Annual running cost (est.) | ~£610/yrLower | ~£625/yr |
| Refrigerant | Varies by model | R32 |
| Country | UK | Ireland |
| UK brand | Yes | No |
| Best for | Price-led switchers happy to go with one vertically integrated provider | Oil and LPG households off the gas grid, especially rural England, Wales and NI |
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 25p/kWh (Ofgem cap average; changes quarterly). Confirm current models and exact pricing with your MCS-certified installer.
Price Comparison
Octopus Cosy starts from £8,000 installed before any support (indicative, June 2026), while Grant Aerona3 starts from £8,000. 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 £500 - £4,500 for Octopus Cosy and £500 - £5,500 for Grant Aerona3 out of pocket. Your MCS-certified installer claims the grant for you.
Efficiency Comparison
SCOP (seasonal coefficient of performance) is the key efficiency metric for a heating heat pump: it measures how many kilowatt-hours of heat you get per kilowatt-hour of electricity across a whole heating season. Octopus Cosy reaches a SCOP of 4.1, while Grant Aerona3 reaches 4. The Octopus Cosy is roughly 2% more efficient on this measure, which on our estimates is worth about £15 a year at Ofgem cap electricity prices, or approximately £150 over ten years. Real-world SCOP depends heavily on system design and flow temperature, which is what the MCS heat-loss survey is for.
Warranty Comparison
Octopus Cosy offers a 5-year unit warranty and 5-year compressor warranty. Grant Aerona3 offers a 5-year unit warranty and 5-year compressor warranty. Both brands offer the same unit warranty length, so coverage is comparable; check what extended terms each installer can register. Workmanship cover for the installation itself comes separately from your installer and should be at least 12 months, 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, and siting is part of the installation assessment. Octopus Cosy operates from 45dB, while Grant Aerona3 runs from 47dB. The Octopus Cosy is quieter at 45dB. At this level it is moderate, similar to a quiet conversation; ask the installer to position the unit away from bedroom windows and boundary walls.
Cold-Weather and Retrofit Suitability
Two things decide how well a unit suits an older UK home: cold-weather output and flow temperature. Octopus Cosy uses a refrigerant that varies by model, while Grant Aerona3 uses R32. Modern units from both brands 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
Octopus Cosy
Pros
- Cheapest mainstream route to a heat pump (avg ~£4,460 post-grant via Octopus)
- UK-designed, end-to-end install by one company
- Tariff pairing cuts running costs
- Grant handled entirely for you
Cons
- Install only through Octopus (no independent quotes on the hardware)
- Newer hardware with a shorter track record
- Standard 5-year warranty
Grant Aerona3
Pros
- The oil-belt specialist - installers know rural retrofits
- Quiet Mark accredited models
- Solid cold-weather output
- Pairs naturally with the £9,000 oil/LPG grant uplift
Cons
- Less common in urban gas-replacement quotes
- Standard warranty unless registered/extended
Which Should You Choose?
Choose Octopus Cosy if...
- You want the best efficiency and lowest running costs (SCOP 4.1 vs 4)
- Quiet operation matters to you (45dB vs 47dB)
- You want lower estimated annual running costs (~£610/yr vs ~£625/yr)
- You want a UK brand with local manufacturing or headquarters behind it
Choose Grant Aerona3 if...
- Oil and LPG households off the gas grid, especially rural England, Wales and NI
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 from 21 July 2026) 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 June 2026.
Where are you?
See indicative costs and local installers for your area