The short answer
A 2023 New Buildings Institute field study reports monitored 120-volt heat-pump water heaters at 32 California customer sites. Its Table 9 gives aggregate weekday and weekend electrical-use averages. These are externally measured study averages, not Watt & Home readings or predictions for every water heater.
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What was observed, and by whom
New Buildings Institute’s July 2023 plug-in heat-pump water-heater field report, hosted in the US Department of Energy’s field database, covers 32 California customer installations. The DOE study record describes monitoring water and ambient temperature, flow and electrical power. Watt & Home did not conduct those measurements.
This article uses the report’s Table 9, printed page 29 / PDF page 35. The values are averages across study sites and day types. They are not consecutive meter readings from one household and should not be entered into a personal journal as though they were.
Read the reported daily electricity averages
| Study grouping | Weekday average | Weekend average |
|---|---|---|
| Summer | 0.97 kWh/day | 0.96 kWh/day |
| Non-summer | 2.07 kWh/day | 2.10 kWh/day |
| Overall | 2.01 kWh/day | 2.05 kWh/day |
The report notes limited summer data because many installations occurred in winter. These group averages are not a controlled seasonal comparison, and they do not define a national average or a range for every individual installation.
Apply a tariff without inventing an observation
To explain the cost arithmetic, assume a constant $0.20/kWh and construct a week with five days at the published overall weekday average and two at its weekend average:
5 × 2.01 + 2 × 2.05 = 14.15 kWh. At the chosen rate, that scenario costs $2.83. This is Watt & Home’s repricing example, not a measured week, an observed study bill or a current California tariff.
Do not multiply a rounded daily dollar display by a month and call it a measured monthly bill. Use unrounded energy and an explicit period. A tariff with time windows also needs the distribution of energy across those windows; a daily total alone cannot reconstruct it.
Keep measured and modeled comparisons distinct
The report separately compares monitored electrical use with modeled prior gas or propane equipment. Energy expressed in kWh for different fuels is not automatically an electricity bill. Do not transfer a converted gas-energy quantity into an electrical tariff field or describe the old equipment as independently submetered electricity.
A purchase or replacement decision needs local tariffs for each fuel, full installation costs and a comparable service boundary. This article makes no payback claim from the daily electrical averages.
Use the lesson with your own water heater
Choose a representative complete-day electrical measurement, record its source and apply your own price. The water-heater calculator supports measured input, a declared electrical year and bounded resistance-heating scenarios. Keep the original meter readings in the journal, with actual sample counts and dates.
A short low-demand sample may not represent colder inlet water, additional occupants or backup-element operation. Repeat observations under documented conditions. Compare like tasks before attributing an energy difference to equipment or settings.
Follow the source back to its limits
Read the original report and DOE study record for the equipment and monitoring context. The table is valuable evidence that actual operating circumstances matter, but it does not establish that your home will reproduce an aggregate mean.
The storage-loss guide explains why electrical input, useful heat and different efficiency metrics should remain distinct. Our own cost examples retain the reported energy units and explicitly label the tariff and constructed routine.