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Home / system #169

Vaillant Arotherm Split

Swanage, Dorset · Mid-terrace · 70 m² · Pre-1900 · 7 kW · radiators · installed by Inafix

Last 30 daysLast 7 days5 Jan – 4 Feb 2026 (winter reference)1–31 Dec 2025

5 Jan – 4 Feb 2026 (winter reference)

721 hourly rows · MID-class heat meter present: yes
4.25efficiency (COP) over 721 hours, from the heat meter
better than 90% of the metered fleet in January 2026
Electricity used
166 kWh
Heat delivered
704 kWh (heat meter)
Estimate without heat meter
flow sensor 2.39 · temperature model 4.46
Mean outdoor temperature
7.4 °C · 268 space-heating hours
Flow temperature at 0 °C outside
23.6 °C (curve slope 0.90 per K)
Flow − return while heating
1.5 K
House needs at −3 °C
2.8 kW (unit rated 7 kW) · fit r² 0.15
Hot water
6% of electricity, COP 1.19
warningOnly 1.5 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 7 kW but the house needs about 2.8 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: “No heat on hot water due to split system”

Day by day

electricity per daydaily COP3.0 floor
electricity, kWh per day07152026-01-05: 10.1 kWh, outside -0.9 °C2026-01-06: 8 kWh, outside 1.8 °C2026-01-07: 4.7 kWh, outside 4.7 °C2026-01-08: 3.6 kWh, outside 6.8 °C2026-01-09: 4.6 kWh, outside 4 °C2026-01-10: 7.7 kWh, outside 1.5 °C2026-01-11: 3.3 kWh, outside 7.7 °C2026-01-12: 2.7 kWh, outside 10.2 °C2026-01-13: 2.7 kWh, outside 10 °C2026-01-14: 3.3 kWh, outside 6.6 °C2026-01-15: 2.8 kWh, outside 8.6 °C2026-01-16: 3 kWh, outside 7.4 °C2026-01-17: 2.9 kWh, outside 8.2 °C2026-01-18: 2.8 kWh, outside 8.7 °C2026-01-19: 2.6 kWh, outside 9.8 °C2026-01-20: 2.7 kWh, outside 8.7 °C2026-01-21: 2.6 kWh, outside 8.9 °C2026-01-22: 3.6 kWh, outside 8.9 °C2026-01-23: 10.4 kWh, outside 7.9 °C2026-01-24: 14.8 kWh, outside 8.3 °C2026-01-25: 13.8 kWh, outside 7.5 °C2026-01-26: 14.8 kWh, outside 7.8 °C2026-01-27: 12.5 kWh, outside 9 °C2026-01-28: 8 kWh, outside 7.3 °C2026-01-29: 3.2 kWh, outside 7.5 °C2026-01-30: 2.9 kWh, outside 8.4 °C2026-01-31: 3.1 kWh, outside 7.8 °C2026-02-01: 2.6 kWh, outside 8 °C2026-02-02: 2.8 kWh, outside 7.9 °C2026-02-03: 3 kWh, outside 7 °C2026-02-04: 0.2 kWh, outside 7.1 °Cdaily COP (heat ÷ electricity)1352026-01-05: COP 3.692026-01-06: COP 3.972026-01-07: COP 4.892026-01-08: COP 5.312026-01-09: COP 4.712026-01-10: COP 3.82026-01-11: COP 5.42026-01-12: COP 5.722026-01-13: COP 5.552026-01-14: COP 4.852026-01-15: COP 5.312026-01-16: COP 5.122026-01-17: COP 5.242026-01-18: COP 5.282026-01-19: COP 5.42026-01-20: COP 5.122026-01-21: COP 5.292026-01-22: COP 5.252026-01-23: COP 4.352026-01-24: COP 3.472026-01-25: COP 3.532026-01-26: COP 3.252026-01-27: COP 3.622026-01-28: COP 3.782026-01-29: COP 4.782026-01-30: COP 4.992026-01-31: COP 4.952026-02-01: COP 4.912026-02-02: COP 4.992026-02-03: COP 5.1501-0501-0901-1301-1701-2101-2501-2902-02
Daily COP needs a heat meter; days without one show electricity only.

The installed heating curve

one heating hourfitted curve50 °C
2030405060-4-2024681012outdoor 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.