A high winter electricity bill does not, by itself, show that a heat pump is inefficient. It combines weather, comfort choices, hot water, other appliances and the price of electricity. A short diary helps separate those factors and gives an installer something concrete to investigate.
Download the 14-day heat pump diary (CSV). This is an observation worksheet, not an engineering assessment. Do not change service settings or disable protective hot-water cycles to improve the figures.
Establish what your reading measures
Start with an existing dedicated meter or the system’s monitoring display. Ask your installer whether the value is measured or estimated and whether it includes the compressor, pumps, backup heater and hot water. Do not combine two displays until you know whether they overlap.
If you only have the whole-house electricity meter, label the reading whole-house consumption. You cannot attribute all of it to heating, especially if an EV, immersion or other large load is running. Subtracting a guessed “normal household baseline” produces an estimate, not a direct heat-pump measurement.
Take readings at the same time each day
For fourteen days, note the date, start and end readings, units, approximate outdoor conditions, comfort level, occupancy and unusual hot-water demand. Where your monitoring supports it, separate consumption by tariff window. A daily difference between cumulative readings gives that day’s energy use.
| Record | Why it helps |
|---|---|
| Electricity used and measurement source | Distinguishes a meter reading from a manufacturer estimate |
| Outdoor conditions | A colder day usually represents a different heating demand |
| Indoor comfort and schedule | A saving caused by an uncomfortably cold house is not an equivalent result |
| Hot-water use and unusual loads | Explains changes unrelated to space heating |
| User changes and any fault codes | Helps the installer relate symptoms to timing |
Keep personal account identifiers out of any version you share. Faults, persistent loss of heat or unusual equipment behaviour should be raised with the installer rather than investigated by opening equipment.
Calculate cost without inventing an efficiency figure
In a fictional day, a dedicated meter records 18 kWh: 12 kWh at 32c and 6 kWh at 16c. The variable electricity cost is €4.80. Applying 16c to all 18 kWh would produce €2.88 and understate the cost. Applying 32c to everything would overstate it at €5.76.
This is the cost of the monitored boundary only. Add an allowance for standing charges when comparing full energy plans, but do not describe the entire electricity standing charge as an extra cost caused by a heat pump if the home already needs that connection.
To assess performance, you also need reliable heat-output data with a matching measurement boundary. For example, 54 kWh of delivered heat divided by 18 kWh of electricity gives a ratio of 3 for that period. It is not a seasonal performance figure. If you do not measure heat output, leave efficiency blank rather than deriving it from the electricity bill.
What to send your installer
Summarise the measurement source, date range, comfort issue, tariff and any recorded faults. Include representative cold and milder days. Ask whether the pattern matches the design and whether the monitoring includes auxiliary heaters.
Two consecutive weeks are not a controlled comparison: weather and occupancy can change. Avoid annualising a single cold day or declaring that a new setting saved a fixed percentage without comparable conditions. After advice from the installer, change one agreed user-level setting at a time and record the result.
The aim is a warm home with explainable running costs. Pair the diary with the quote and handover checklist if your system is newly installed.
