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Home / system #835

Vaillant Arotherm+

Pembrokeshire · End-terrace · 86 m² · 1900 to 1939 · 3.5 kW · underfloor · installed by Renewable Future Wales

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

5 Jan – 4 Feb 2026 (winter reference)

419 hourly rows · MID-class heat meter present: yes
3.67efficiency (COP) over 419 hours, from the heat meter
better than 50% of the metered fleet in January 2026
Electricity used
255 kWh
Heat delivered
936 kWh (heat meter)
Estimate without heat meter
flow sensor 3.57 · temperature model 3.76
Mean outdoor temperature
6.6 °C · 358 space-heating hours · cooling 0 kWh removed (2 kWh electricity), kept out of the COP
Flow temperature at 0 °C outside
37.2 °C (curve slope -0.55 per K)
Flow − return while heating
2.5 K
House needs at −3 °C
3.7 kW (unit rated 3.5 kW) · fit r² 0.24
Hot water
12% of electricity, COP 1.32
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.
valueReaching the fleet’s January median (3.69) would have saved about £0 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 day011232026-01-05: 22.3 kWh, outside 1.5 °C2026-01-06: 21.1 kWh, outside 4.6 °C2026-01-07: 15.9 kWh, outside 6.5 °C2026-01-08: 17.1 kWh, outside 4.9 °C2026-01-09: 22.8 kWh, outside 5.2 °C2026-01-10: 19 kWh, outside 5.1 °C2026-01-11: 11.1 kWh, outside 9.8 °C2026-01-12: 10.8 kWh, outside 10.5 °C2026-01-13: 11.4 kWh, outside 7.3 °C2026-01-14: 18.7 kWh, outside 4.8 °C2026-01-15: 12.7 kWh, outside 6.7 °C2026-01-16: 12.8 kWh, outside 7.4 °C2026-01-17: 9.7 kWh, outside 7.6 °C2026-01-18: 11.6 kWh, outside 6.3 °C2026-01-19: 12.5 kWh, outside 6.8 °C2026-01-20: 12.1 kWh, outside 7.2 °C2026-01-21: 10.4 kWh, outside 8.4 °C2026-01-22: 5.3 kWh, outside 8.7 °Cdaily COP (heat ÷ electricity)1352026-01-05: COP 2.922026-01-06: COP 3.222026-01-07: COP 3.672026-01-08: COP 3.312026-01-09: COP 3.422026-01-10: COP 3.342026-01-11: COP 4.332026-01-12: COP 4.452026-01-13: COP 3.842026-01-14: COP 3.322026-01-15: COP 3.852026-01-16: COP 3.912026-01-17: COP 3.922026-01-18: COP 4.342026-01-19: COP 4.032026-01-20: COP 4.032026-01-21: COP 3.92026-01-22: COP 3.2401-0501-0701-0901-1101-1301-1501-1701-1901-21
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
2030405060-2024681012outdoor 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.