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Home / system #1344

Vaillant Arotherm+

Woking, Surrey · Detached · 262 m² · 1900 to 1939 · 12 kW · underfloor · installed by Urban Plumbers Ltd

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

Last 7 days

169 hourly rows · MID-class heat meter present: yes
5.09efficiency (COP) over 169 hours, from the heat meter
better than 99% of the metered fleet in January 2026
Electricity used
116 kWh
Heat delivered
588 kWh (heat meter)
Estimate without heat meter
flow sensor 4.78 · temperature model 4.68
Mean outdoor temperature
9.2 °C · 144 space-heating hours
Flow temperature at 0 °C outside
36.1 °C (curve slope -0.61 per K)
Flow − return while heating
1.5 K
House needs at −3 °C
5.2 kW (unit rated 12 kW) · fit r² 0.07
Hot water
17% of electricity, COP 4.18
warningOnly 1.5 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.
infoUnit is rated 12 kW but the house needs about 5.2 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.

Day by day

electricity per daydaily COP3.0 floor
electricity, kWh per day09192026-10-31: 8.7 kWh, outside 11.6 °C2026-11-01: 16.1 kWh, outside 8.8 °C2026-11-02: 15.3 kWh, outside 9.8 °C2026-11-03: 15.5 kWh, outside 9.9 °C2026-11-04: 16.1 kWh, outside 9.5 °C2026-11-05: 16.3 kWh, outside 9.2 °C2026-11-06: 18.7 kWh, outside 8.3 °C2026-11-07: 8.7 kWh, outside 4.5 °Cdaily COP (heat ÷ electricity)1352026-10-31: COP 5.162026-11-01: COP 5.092026-11-02: COP 5.332026-11-03: COP 5.262026-11-04: COP 5.132026-11-05: COP 5.122026-11-06: COP 4.942026-11-07: COP 4.5210-3111-0111-0211-0311-0411-0511-0611-07
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
20304050603579111315outdoor 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.