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Viessmann Vitocal 150A

Bentlawnt, Shropshire · Detached · 140 m² · 2012 or newer · 10 kW · underfloor · installed by Josh Stead

Last 30 days Last 7 days 5 Jan – 4 Feb 2026 (winter reference)1–31 Dec 2025

Last 30 days

105 hourly rows · MID-class heat meter present: yes

5.32efficiency (COP) over 105 hours, from the heat meter
better than 99% of the metered fleet in January 2026

Electricity used: 62 kWh
Heat delivered: 331 kWh (heat meter)
Estimate without heat meter: flow sensor 5.38 · temperature model 4.65
Mean outdoor temperature: 8.6 °C · 86 space-heating hours · cooling 0 kWh removed (0 kWh electricity), kept out of the COP
Flow temperature at 0 °C outside: 31.0 °C (curve slope -0.06 per K)
Flow − return while heating: 3.8 K
House needs at −3 °C: 3.5 kW (unit rated 10 kW) · fit r² 0.00
Hot water: 11% of electricity, COP 4.38

infoUnit is rated 10 kW but the house needs about 3.5 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

Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °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.