Mitsubishi Ecodan vs Daikin Altherma 3 (UK 2026)

Mitsubishi Ecodan and Daikin Altherma 3 sit at the top of the UK premium air-source heat pump market. Both are MCS-certified, both qualify for the Boiler Upgrade Scheme £7,500 grant, both have UK-wide installer networks, and both will heat a typical UK home effectively for 15-20 years with reasonable servicing. The differences come down to noise, retrofit suitability for high-flow-temperature radiators, installer availability in your postcode, and a £2,000-£3,000 list-price gap that tips toward Daikin on raw economics.

SCOP (Seasonal Coefficient of Performance) is the headline efficiency metric the UK MCS product list uses to certify heat pumps. Higher SCOP = more heat delivered per unit of electricity consumed across a typical UK heating season.

Mitsubishi Ecodan PUZ-WM: SCOP rated 4.0-4.4 across the 5-14kW capacity range (per Mitsubishi Electric data sheets). The 8.5kW model commonly fitted in UK 3-bed semis returns SCOP 4.2 at 35°C flow temperature - meaning 4.2 kWh of heat per 1 kWh of electricity. A++ Energy Label rating across the range.

Daikin Altherma 3 H HT EHVH: SCOP 3.9-4.3 across the 4-16kW range (per Daikin data sheets). The 8kW model returns SCOP 4.1 at 35°C. A++ Energy Label rating. The higher-temperature variants (Altherma 3 H HT) trade some efficiency for the higher flow temperature - SCOP drops to ~3.5-3.8 at 55°C flow versus ~4.1 at 35°C.

The honest framing: at typical UK retrofit flow temperatures (45-50°C), both units perform within 5-8% of each other. The £2,000-£3,000 capital saving on the Altherma 3 covers many years of the marginal Ecodan efficiency advantage. The SCOP gap is not the deciding factor for most installs.

The single most-cited Ecodan advantage is operational noise. The numbers from the MCS product list sound levels:

Ecodan PUZ-WM85: 44 dB(A) at 1m, 36 dB(A) at 4m. Sound power 56 dB(A). The 11.2kW variant is 46/38 dB(A).

Altherma 3 H 8kW (EHVH08): 48 dB(A) at 1m, 40 dB(A) at 4m. Sound power 61 dB(A). The 12kW variant is 50/42 dB(A).

The 4-6 dB(A) gap is meaningful - 3 dB is the threshold of perceptible difference, and 6 dB is doubling perceived loudness. For a unit positioned 1.5m from a neighbour's boundary (common for UK semis with narrow side returns), the Ecodan is genuinely the quieter neighbour-friendly choice. The MCS planning permitted-development rules set a 42 dB(A) limit at 1m from the nearest neighbouring property - the Ecodan typically passes at 1.5m boundary distance, the Altherma 3 may need acoustic enclosure or further setback to clear the limit.

For detached homes with wide gardens, the noise difference is academic. For terraced or close-spaced semi-detached homes, it's potentially the deciding spec.

This is where the Altherma 3 has its biggest advantage. The standard rule of thumb for heat pump retrofits is to upsize radiators so the system can run at 35-45°C flow temperature - which gives the best SCOP performance. But upsizing every radiator in a 4-bed semi typically costs £3,000-£6,000 and adds 6-12 weeks to the install timeline.

The Daikin Altherma 3 H HT variant runs reliably at 65-70°C flow temperature - the same temperature range as a gas combi boiler. This means you can install the heat pump on existing radiators without upsizing them, at the cost of some efficiency. The total install cost saving (no radiator upgrades) typically beats the lifetime efficiency loss for older housing stock.

The Mitsubishi Ecodan standard range tops out at ~55°C flow temperature. Mitsubishi sells a CAHV-P range that goes higher but it's primarily commercial-grade and meaningfully more expensive than the Altherma 3 H HT.

For a UK 1930s or pre-war semi with cast-iron radiators or undersized panel radiators, the Altherma 3 H HT is the more realistic retrofit. For a modern (post-2000) home with appropriately sized panel radiators that can already deliver heat at 45°C flow, the Ecodan is the more efficient choice and the noise advantage tips the decision.

Per a typical 3-bed UK semi (8kW capacity, indoor cylinder, basic controls, no radiator upgrades):

Mitsubishi Ecodan 8.5kW supply-only: £8,500-£9,500. Installation by MCS-registered installer: £4,500-£6,500. Cylinder (180L): £1,200-£1,800. Total install: £14,200-£17,800. After £7,500 BUS grant: £6,700-£10,300 out of pocket.

Daikin Altherma 3 H 8kW supply-only: £6,500-£7,500. Installation by MCS-registered installer: £4,500-£6,500. Cylinder (180L): £1,200-£1,800. Total install: £12,200-£15,800. After £7,500 BUS grant: £4,700-£8,300 out of pocket.

The Altherma 3 saves £2,000-£3,000 out of pocket at install time. Whether that's worth it depends on the noise tolerance, the retrofit complexity (radiator upgrades or not), and whether your local installer is Mitsubishi- or Daikin-trained. The post-grant prices above include the BUS grant being processed via your installer; both manufacturers have UK-wide MCS-registered installer networks who handle the grant administration.

Pick Mitsubishi Ecodan if: noise matters (you have neighbours within 3m of the proposed install location), you have a modern home with appropriately-sized radiators that can deliver heat at 45°C, you have £2-3k budget headroom over the Altherma 3, and your local MCS-registered installer is Mitsubishi-trained.

Pick Daikin Altherma 3 H HT if: your home is pre-2000 with smaller radiators that need ≥55°C flow temperature, you want to save £2,000-£3,000 at install time, you have garden space for the slightly larger outdoor unit (1.4m wide vs 1.1m for the Ecodan), and your local MCS-registered installer is Daikin-trained.

Use the installer network as the tiebreaker. Both units are excellent. The single biggest factor in a successful heat pump install is having an installer who has fitted dozens of the same model before. If your three best local quotes are from Mitsubishi-trained installers, take the Ecodan; if they're Daikin-trained, take the Altherma 3.