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Home / system #785

Vailllant Arotherm+

Cheltenham, Gloucestershire · Semi-detached · 115 m² · 1940 to 1982 · 7 kW · radiators · installed by Custom Renewables

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

5 Jan – 4 Feb 2026 (winter reference)

721 hourly rows · MID-class heat meter present: yes
4.10efficiency (COP) over 721 hours, from the heat meter
better than 81% of the metered fleet in January 2026
Electricity used
326 kWh
Heat delivered
1334 kWh (heat meter)
Estimate without heat meter
flow sensor 3.99 · temperature model 4.37
Mean outdoor temperature
5.8 °C · 566 space-heating hours
Flow temperature at 0 °C outside
30.2 °C (curve slope -0.29 per K)
Flow − return while heating
1.7 K
House needs at −3 °C
2.9 kW (unit rated 7 kW) · fit r² 0.05
Hot water
no hot-water flag in data
warningOnly 1.7 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 7 kW but the house needs about 2.9 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 day011232026-01-05: 22.7 kWh, outside -1.3 °C2026-01-06: 18.7 kWh, outside 1 °C2026-01-07: 11.7 kWh, outside 4.2 °C2026-01-08: 12.7 kWh, outside 3.3 °C2026-01-09: 15.5 kWh, outside 3 °C2026-01-10: 19.5 kWh, outside 0.9 °C2026-01-11: 11.7 kWh, outside 6.7 °C2026-01-12: 6.6 kWh, outside 10.1 °C2026-01-13: 6.8 kWh, outside 7.8 °C2026-01-14: 14.7 kWh, outside 2.5 °C2026-01-15: 9.2 kWh, outside 6.8 °C2026-01-16: 10.1 kWh, outside 6 °C2026-01-17: 9.6 kWh, outside 6.8 °C2026-01-18: 8.6 kWh, outside 6.1 °C2026-01-19: 6.6 kWh, outside 7.5 °C2026-01-20: 8.6 kWh, outside 8.2 °C2026-01-21: 9.1 kWh, outside 7.7 °C2026-01-22: 7.4 kWh, outside 8.9 °C2026-01-23: 9.3 kWh, outside 7.2 °C2026-01-24: 9 kWh, outside 7.7 °C2026-01-25: 9.1 kWh, outside 6.9 °C2026-01-26: 9.9 kWh, outside 5.3 °C2026-01-27: 8.4 kWh, outside 7.7 °C2026-01-28: 11.5 kWh, outside 5.3 °C2026-01-29: 11.9 kWh, outside 4.5 °C2026-01-30: 9.5 kWh, outside 7.2 °C2026-01-31: 8.5 kWh, outside 7.4 °C2026-02-01: 9.1 kWh, outside 7.1 °C2026-02-02: 8.7 kWh, outside 7 °C2026-02-03: 10.7 kWh, outside 4.2 °C2026-02-04: 0.1 kWh, outside 1.9 °Cdaily COP (heat ÷ electricity)1352026-01-05: COP 3.082026-01-06: COP 3.382026-01-07: COP 4.252026-01-08: COP 4.152026-01-09: COP 3.642026-01-10: COP 3.152026-01-11: COP 4.22026-01-12: COP 4.722026-01-13: COP 4.742026-01-14: COP 3.512026-01-15: COP 4.492026-01-16: COP 4.252026-01-17: COP 4.482026-01-18: COP 4.472026-01-19: COP 4.852026-01-20: COP 4.512026-01-21: COP 4.562026-01-22: COP 4.632026-01-23: COP 4.462026-01-24: COP 4.392026-01-25: COP 4.412026-01-26: COP 4.252026-01-27: COP 4.692026-01-28: COP 4.022026-01-29: COP 4.222026-01-30: COP 4.482026-01-31: COP 4.452026-02-01: COP 4.342026-02-02: COP 4.462026-02-03: COP 4.3301-0501-0901-1301-1701-2101-2501-2902-02
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
2030405060-7-4-125811outdoor 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.