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MasterTherm BA221

Lincolnshire · Bungalow · 80 m² · 1940 to 1982 · 7.7 kW · underfloor · installed by Andy Brown

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

4.15efficiency (COP) over 169 hours, from the heat meter
better than 84% of the metered fleet in January 2026

Electricity used: 73 kWh
Heat delivered: 303 kWh (heat meter)
Estimate without heat meter: flow sensor 4.10 · temperature model 4.85
Mean outdoor temperature: 10.2 °C · 78 space-heating hours · cooling 1 kWh removed (0 kWh electricity), kept out of the COP
Flow temperature at 0 °C outside: 30.3 °C (curve slope -0.06 per K)
Flow − return while heating: 3.1 K
House needs at −3 °C: 3.4 kW (unit rated 7.7 kW) · fit r² 0.00
Hot water: 30% of electricity, COP 2.94

infoUnit is rated 7.7 kW but the house needs about 3.4 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.