Home / system #786

Viessmann 150a

Byfield, Northamptonshire · Detached · 200 m² · 1900 to 1939 · 16 kW · radiators · installed by Custom Renewables

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

3.91efficiency (COP) over 169 hours, from the heat meter
better than 66% of the metered fleet in January 2026

Electricity used: 147 kWh
Heat delivered: 573 kWh (heat meter)
Estimate without heat meter: flow sensor 3.57 · temperature model 3.88
Mean outdoor temperature: 8.1 °C · 147 space-heating hours
Flow temperature at 0 °C outside: 30.5 °C (curve slope 0.66 per K)
Flow − return while heating: 2.2 K
House needs at −3 °C: 6.7 kW (unit rated 16 kW) · fit r² 0.08
Hot water: no hot-water flag in data

warningOnly 2.2 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.

seriousCompressor starts about 7.5 times per hour

Short cycling wears the compressor and cuts efficiency. Usual fixes: remove or bypass a buffer, open zone valves, lower the curve, raise minimum run time.

warningUnit is rated 16 kW but the house needs about 6.7 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.

noteOwner’s note on the source site: “Negative heat not reported”

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.