Home / system #1094

Viessmann Vitocal 150A

Tring, Hertfordshire · Semi-detached · 153 m² · 1900 to 1939 · 10 kW · radiators · installed by CHALK

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

Last 7 days

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

4.44efficiency (COP) over 169 hours, from the heat meter
better than 92% of the metered fleet in January 2026

Electricity used: 93 kWh
Heat delivered: 415 kWh (heat meter)
Estimate without heat meter: flow sensor 4.53 · temperature model 4.57
Mean outdoor temperature: 8.4 °C · 119 space-heating hours · cooling 0 kWh removed (0 kWh electricity), kept out of the COP
Flow temperature at 0 °C outside: 30.4 °C (curve slope -0.09 per K)
Flow − return while heating: 2.3 K
House needs at −3 °C: 4.1 kW (unit rated 10 kW) · fit r² 0.03
Hot water: 26% of electricity, COP 4.25

warningOnly 2.3 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 4.1 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.

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.