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Home / system #652

Vaillant Arotherm+

Milton Keynes, Buckinghamshire · Detached · 149 m² · 1983 to 2011 · 7 kW · underfloor · installed by Custom Renewables

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

Last 30 days

721 hourly rows · MID-class heat meter present: yes
4.81efficiency (COP) over 721 hours, from the heat meter
better than 98% of the metered fleet in January 2026
Electricity used
226 kWh
Heat delivered
1090 kWh (heat meter)
Estimate without heat meter
flow sensor 5.03 · temperature model 5.17
Mean outdoor temperature
10.8 °C · 345 space-heating hours · cooling 0 kWh removed (0 kWh electricity), kept out of the COP
Flow temperature at 0 °C outside
34.7 °C (curve slope -0.58 per K)
Flow − return while heating
1.9 K
House needs at −3 °C
7.0 kW (unit rated 7 kW) · fit r² 0.54
Hot water
22% of electricity, COP 3.54
warningOnly 1.9 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 day06122026-10-08: 4.5 kWh, outside 11.7 °C2026-10-09: 2.7 kWh, outside 14.7 °C2026-10-10: 5.7 kWh, outside 10.7 °C2026-10-11: 5.6 kWh, outside 10.7 °C2026-10-12: 3.5 kWh, outside 14.2 °C2026-10-13: 2.3 kWh, outside 15.9 °C2026-10-14: 3.4 kWh, outside 13.1 °C2026-10-15: 1.8 kWh, outside 16.8 °C2026-10-16: 6 kWh, outside 11.4 °C2026-10-17: 9.1 kWh, outside 8.5 °C2026-10-18: 9.4 kWh, outside 9.4 °C2026-10-19: 8.8 kWh, outside 10.9 °C2026-10-20: 6.9 kWh, outside 11.1 °C2026-10-21: 9.9 kWh, outside 8.2 °C2026-10-22: 7.9 kWh, outside 10.3 °C2026-10-23: 9.1 kWh, outside 9.9 °C2026-10-24: 8.9 kWh, outside 9.7 °C2026-10-25: 9.7 kWh, outside 10.2 °C2026-10-26: 6.9 kWh, outside 11.6 °C2026-10-27: 6 kWh, outside 13 °C2026-10-28: 7.9 kWh, outside 10.7 °C2026-10-29: 6.4 kWh, outside 11.6 °C2026-10-30: 6.8 kWh, outside 11.3 °C2026-10-31: 7.6 kWh, outside 9.4 °C2026-11-01: 9.8 kWh, outside 8.5 °C2026-11-02: 9.7 kWh, outside 8.8 °C2026-11-03: 11.1 kWh, outside 8.7 °C2026-11-04: 12 kWh, outside 8.9 °C2026-11-05: 11.9 kWh, outside 8.5 °C2026-11-06: 10.7 kWh, outside 8.7 °C2026-11-07: 4.6 kWh, outside 4.2 °Cdaily COP (heat ÷ electricity)1352026-10-08: COP 4.612026-10-09: COP 4.612026-10-10: COP 4.82026-10-11: COP 4.752026-10-12: COP 4.482026-10-13: COP 3.742026-10-14: COP 4.812026-10-15: COP 4.352026-10-16: COP 4.872026-10-17: COP 4.792026-10-18: COP 4.862026-10-19: COP 4.882026-10-20: COP 5.282026-10-21: COP 4.942026-10-22: COP 4.932026-10-23: COP 4.822026-10-24: COP 4.952026-10-25: COP 4.672026-10-26: COP 5.342026-10-27: COP 5.162026-10-28: COP 4.82026-10-29: COP 5.212026-10-30: COP 4.792026-10-31: COP 4.952026-11-01: COP 4.732026-11-02: COP 4.912026-11-03: COP 4.852026-11-04: COP 4.662026-11-05: COP 4.712026-11-06: COP 4.742026-11-07: COP 3.4710-0810-1210-1610-2010-2410-2811-0111-05
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
2030405060246810121416outdoor 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.