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Home / system #445

Vaillant Arotherm+

Hackney, London · End-terrace · 82.1 m² · 1940 to 1982 · 3.5 kW · radiators · installed by Hilton Warm & Cool London

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
1.76efficiency (COP) over 721 hours, from the heat meter
better than 1% of the metered fleet in January 2026
Electricity used
107 kWh
Heat delivered
187 kWh (heat meter)
Estimate without heat meter
flow sensor 2.08 · temperature model 5.46
Mean outdoor temperature
12.3 °C · 173 space-heating hours
Flow temperature at 0 °C outside
23.5 °C (curve slope 0.61 per K)
Flow − return while heating
2.0 K
House needs at −3 °C
1.1 kW (unit rated 3.5 kW) · fit r² 0.03
Hot water
no hot-water flag in data
seriousWinter efficiency 1.76 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.
warningOnly 2 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.
infoUnit is rated 3.5 kW but the house needs about 1.1 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 £14 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 day0372026-10-08: 1.6 kWh, outside 12.9 °C2026-10-09: 2.2 kWh, outside 16 °C2026-10-10: 2.8 kWh, outside 12.4 °C2026-10-11: 2.9 kWh, outside 12.8 °C2026-10-12: 2 kWh, outside 15.4 °C2026-10-13: 3.2 kWh, outside 17.5 °C2026-10-14: 1.6 kWh, outside 14.5 °C2026-10-15: 1.2 kWh, outside 17.8 °C2026-10-16: 1.6 kWh, outside 13.4 °C2026-10-17: 2.6 kWh, outside 10.6 °C2026-10-18: 3.7 kWh, outside 10.8 °C2026-10-19: 2.8 kWh, outside 11.8 °C2026-10-20: 5.2 kWh, outside 12.1 °C2026-10-21: 3.3 kWh, outside 10 °C2026-10-22: 3.9 kWh, outside 12.2 °C2026-10-23: 4.1 kWh, outside 10.8 °C2026-10-24: 4.6 kWh, outside 10.8 °C2026-10-25: 4.1 kWh, outside 11.5 °C2026-10-26: 4 kWh, outside 12.8 °C2026-10-27: 5.4 kWh, outside 14.3 °C2026-10-28: 3 kWh, outside 12.1 °C2026-10-29: 2.8 kWh, outside 13.6 °C2026-10-30: 3.1 kWh, outside 12.1 °C2026-10-31: 3.8 kWh, outside 11.4 °C2026-11-01: 4.1 kWh, outside 10.2 °C2026-11-02: 4.4 kWh, outside 10.3 °C2026-11-03: 6.5 kWh, outside 10.2 °C2026-11-04: 3.7 kWh, outside 10 °C2026-11-05: 5.1 kWh, outside 9.9 °C2026-11-06: 5 kWh, outside 10 °C2026-11-07: 1.9 kWh, outside 5.4 °Cdaily COP (heat ÷ electricity)1352026-10-26: COP 0.432026-10-27: COP 3.142026-10-28: COP 3.862026-10-29: COP 3.112026-10-30: COP 3.872026-10-31: COP 3.582026-11-01: COP 3.832026-11-02: COP 4.042026-11-03: COP 3.382026-11-04: COP 4.412026-11-05: COP 4.142026-11-06: COP 4.142026-11-07: COP 4.2510-0810-1210-1610-2010-2410-2811-0111-05
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
2030405060703579111315outdoor 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.