Heatproof
Home / system #479

Vaillant Arotherm+

Rowledge Surrey · Detached · 400 m² · 1983 to 2011 · 10 kW · underfloor

1–31 Dec 2025

745 hourly rows · MID-class heat meter present: yes
4.85efficiency (COP) over 745 hours, from the heat meter
better than 98% of the metered fleet in January 2026
Electricity used
784 kWh
Heat delivered
3800 kWh (heat meter)
Estimate without heat meter
flow sensor 4.71 · temperature model 4.54
Mean outdoor temperature
7.3 °C · 642 space-heating hours
Flow temperature at 0 °C outside
31.8 °C (curve slope -0.52 per K)
Flow − return while heating
2.5 K
House needs at −3 °C
9.5 kW (unit rated 10 kW) · fit r² 0.33
Hot water
14% of electricity, COP 3.97
warningOnly 2.5 K between flow and return
Circulation pump may be set too high or emitters are undersized for the low flow temperature. Ask the installer to check pump speed.

Day by day

electricity per daydaily COP3.0 floor
electricity, kWh per day027552025-12-01: 13.3 kWh, outside 9.9 °C2025-12-02: 16.6 kWh, outside 8 °C2025-12-03: 30.3 kWh, outside 6.1 °C2025-12-04: 24.6 kWh, outside 6.3 °C2025-12-05: 38.3 kWh, outside 5.6 °C2025-12-06: 18.7 kWh, outside 9.9 °C2025-12-07: 14.7 kWh, outside 11.1 °C2025-12-08: 14.9 kWh, outside 12 °C2025-12-09: 13.4 kWh, outside 12.1 °C2025-12-10: 16.9 kWh, outside 10.2 °C2025-12-11: 17.5 kWh, outside 9.3 °C2025-12-12: 16.8 kWh, outside 9 °C2025-12-13: 27.8 kWh, outside 6.8 °C2025-12-14: 20.2 kWh, outside 9 °C2025-12-15: 15.3 kWh, outside 10 °C2025-12-16: 18.5 kWh, outside 8.5 °C2025-12-17: 31.6 kWh, outside 6 °C2025-12-18: 14.7 kWh, outside 10.7 °C2025-12-19: 23.6 kWh, outside 7.7 °C2025-12-20: 32.2 kWh, outside 6.2 °C2025-12-21: 17.4 kWh, outside 8.8 °C2025-12-22: 16 kWh, outside 9.3 °C2025-12-23: 23.1 kWh, outside 6.6 °C2025-12-24: 38.7 kWh, outside 4.5 °C2025-12-25: 46.7 kWh, outside 3.1 °C2025-12-26: 39.9 kWh, outside 3.5 °C2025-12-27: 27.4 kWh, outside 4.8 °C2025-12-28: 26.2 kWh, outside 5.9 °C2025-12-29: 31.4 kWh, outside 4.6 °C2025-12-30: 38.7 kWh, outside 3.1 °C2025-12-31: 54.8 kWh, outside -1.1 °C2026-01-01: 3.2 kWh, outside -1.2 °Cdaily COP (heat ÷ electricity)1352025-12-01: COP 5.642025-12-02: COP 5.552025-12-03: COP 4.162025-12-04: COP 5.442025-12-05: COP 3.972025-12-06: COP 5.792025-12-07: COP 5.312025-12-08: COP 6.272025-12-09: COP 6.172025-12-10: COP 6.042025-12-11: COP 5.682025-12-12: COP 5.942025-12-13: COP 4.922025-12-14: COP 5.432025-12-15: COP 6.052025-12-16: COP 5.932025-12-17: COP 4.092025-12-18: COP 6.232025-12-19: COP 5.452025-12-20: COP 4.172025-12-21: COP 5.92025-12-22: COP 6.012025-12-23: COP 5.632025-12-24: COP 4.722025-12-25: COP 4.112025-12-26: COP 4.292025-12-27: COP 4.312025-12-28: COP 5.372025-12-29: COP 4.422025-12-30: COP 4.322025-12-31: COP 3.192026-01-01: COP 2.8312-0112-0512-0912-1312-1712-2112-2512-29
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
2030405060-5-21471013outdoor 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.