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Home / system #931

Daikin Altherma 3

Stratford-upon-Avon, West Midlands · Mid-terrace · 153 m² · Pre-1900 · 16 kW · radiators · installed by BUTCO Heating Ltd

Last 30 daysLast 7 days5 Jan – 4 Feb 2026 (winter reference)1–31 Dec 2025

1–31 Dec 2025

418 hourly rows · MID-class heat meter present: yes
2.20efficiency (COP) over 418 hours, from the heat meter
better than 1% of the metered fleet in January 2026
Electricity used
761 kWh
Heat delivered
1672 kWh (heat meter)
Estimate without heat meter
flow sensor 2.15 · temperature model 3.21
Mean outdoor temperature
6.1 °C · 229 space-heating hours · cooling 5 kWh removed (2 kWh electricity), kept out of the COP
Flow temperature at 0 °C outside
38.8 °C (curve slope -0.24 per K)
Flow − return while heating
4.2 K
House needs at −3 °C
7.2 kW (unit rated 16 kW) · fit r² 0.19
Hot water
35% of electricity, COP 2.10
seriousWinter efficiency 2.2 is below the 3.0 floor used for German subsidies
Ask the installer for a commissioning check; the causes are usually flow temperature, hot water settings, or sizing, all listed below.
warningHot water uses 35% of electricity at COP 2.1
Lower the tank target to 45–48 °C, heat water once a day in the warmest hours, and disable weekly legionella cycles unless required.
infoUnit is rated 16 kW but the house needs about 7.2 kW at −3 °C
Oversizing causes cycling in mild weather. Cannot be fixed cheaply now, but the curve and minimum run time can limit the damage.
valueReaching the fleet’s January median (3.69) would have saved about £77 in this window at 0.25 GBP/kWh. An estimate, not a promise.

Day by day

electricity per daydaily COP3.0 floor
electricity, kWh per day037742025-12-14: 10.6 kWh, outside 11.2 °C2025-12-15: 17.7 kWh, outside 10.6 °C2025-12-16: 30.7 kWh, outside 6.3 °C2025-12-17: 39.8 kWh, outside 6.1 °C2025-12-18: 25.5 kWh, outside 9.8 °C2025-12-19: 31.6 kWh, outside 7.1 °C2025-12-20: 42.1 kWh, outside 5.7 °C2025-12-21: 30.9 kWh, outside 8.7 °C2025-12-22: 25.4 kWh, outside 9.4 °C2025-12-23: 32.6 kWh, outside 6.8 °C2025-12-24: 63.2 kWh, outside 4.6 °C2025-12-25: 72.2 kWh, outside 3.8 °C2025-12-26: 70.8 kWh, outside 3.7 °C2025-12-27: 67.8 kWh, outside 4.5 °C2025-12-28: 33.5 kWh, outside 5.7 °C2025-12-29: 40.5 kWh, outside 5.2 °C2025-12-30: 53.1 kWh, outside 4.1 °C2025-12-31: 73.7 kWh, outside -0.3 °C2026-01-01: 1.7 kWh, outside 2 °Cdaily COP (heat ÷ electricity)1352025-12-15: COP 22025-12-16: COP 1.992025-12-17: COP 2.32025-12-18: COP 3.322025-12-19: COP 2.842025-12-20: COP 2.522025-12-21: COP 3.542025-12-22: COP 3.22025-12-23: COP 2.92025-12-24: COP 1.782025-12-25: COP 1.72025-12-26: COP 1.632025-12-27: COP 22025-12-28: COP 2.932025-12-29: COP 2.322025-12-30: COP 1.962025-12-31: COP 1.72026-01-01: COP 3.0312-1412-1612-1812-2012-2212-2412-2612-2812-3001-01
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
2030405060-5-3-11357911outdoor temperature, °Cflow temperature, °C
Each point is one hour of space heating. Lower and flatter is cheaper; well-set radiator systems sit around 35–42 °C at 0 °C outside.
Public system published by its owner on HeatpumpMonitor.org. Cycling (starts per hour) comes from the site’s 365-day statistic. Findings use installer rules of thumb; see methodology.