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Home / system #307

Viessmann Vitocal 151A

Great Haseley, Oxfordshire · Detached · 212 m² · 2012 or newer · 10 kW · underfloor · installed by Harveys & JMR

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
381 kWh
Heat delivered
1832 kWh (heat meter)
Estimate without heat meter
flow sensor 5.10 · temperature model 4.82
Mean outdoor temperature
10.8 °C · 465 space-heating hours
Flow temperature at 0 °C outside
29.4 °C (curve slope 0.11 per K)
Flow − return while heating
2.4 K
House needs at −3 °C
4.7 kW (unit rated 10 kW) · fit r² 0.03
Hot water
no hot-water flag in data
warningOnly 2.4 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 10 kW but the house needs about 4.7 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 day010192026-10-08: 5.3 kWh, outside 11.7 °C2026-10-09: 6.6 kWh, outside 15.3 °C2026-10-10: 12.1 kWh, outside 11 °C2026-10-11: 10.1 kWh, outside 11.5 °C2026-10-12: 7 kWh, outside 15.3 °C2026-10-13: 7.9 kWh, outside 15.7 °C2026-10-14: 8.4 kWh, outside 13.1 °C2026-10-15: 5.2 kWh, outside 16.8 °C2026-10-16: 9.7 kWh, outside 11.6 °C2026-10-17: 13.5 kWh, outside 7 °C2026-10-18: 13.9 kWh, outside 7.5 °C2026-10-19: 11.2 kWh, outside 10 °C2026-10-20: 12.9 kWh, outside 10.6 °C2026-10-21: 16 kWh, outside 8.5 °C2026-10-22: 12.4 kWh, outside 10.9 °C2026-10-23: 14.9 kWh, outside 9.7 °C2026-10-24: 14.5 kWh, outside 10.4 °C2026-10-25: 16.5 kWh, outside 10.5 °C2026-10-26: 10.5 kWh, outside 12.1 °C2026-10-27: 12.2 kWh, outside 12.7 °C2026-10-28: 11.3 kWh, outside 11 °C2026-10-29: 11 kWh, outside 12 °C2026-10-30: 11.7 kWh, outside 11.1 °C2026-10-31: 11.4 kWh, outside 10 °C2026-11-01: 18 kWh, outside 8 °C2026-11-02: 16.6 kWh, outside 8.7 °C2026-11-03: 18.6 kWh, outside 8.1 °C2026-11-04: 16.9 kWh, outside 8.8 °C2026-11-05: 19 kWh, outside 8.5 °C2026-11-06: 16.3 kWh, outside 8.3 °C2026-11-07: 9.3 kWh, outside 3.5 °Cdaily COP (heat ÷ electricity)1352026-10-08: COP 4.342026-10-09: COP 5.022026-10-10: COP 4.862026-10-11: COP 4.512026-10-12: COP 3.092026-10-13: COP 4.552026-10-14: COP 4.222026-10-15: COP 3.642026-10-16: COP 5.252026-10-17: COP 5.022026-10-18: COP 4.952026-10-19: COP 4.522026-10-20: COP 5.192026-10-21: COP 5.212026-10-22: COP 5.142026-10-23: COP 5.212026-10-24: COP 5.162026-10-25: COP 5.412026-10-26: COP 4.122026-10-27: COP 5.182026-10-28: COP 4.812026-10-29: COP 5.162026-10-30: COP 5.12026-10-31: COP 4.962026-11-01: COP 4.652026-11-02: COP 4.692026-11-03: COP 4.612026-11-04: COP 4.922026-11-05: COP 4.812026-11-06: COP 4.652026-11-07: COP 3.8510-0810-1210-1610-2010-2410-2811-0111-05
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
2030405060-20246810121416outdoor 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.