A. O. SMITH PETX-40 1**

The registry lists a UEF, the ratio of hot water delivered to energy used, of 0.92 for this model. This site calculated the annual figure from that UEF and the test's daily hot-water draw for the medium draw pattern, which represents a typical household on a busy morning. The result is 3,531 kWh a year. The registry does not publish this annual figure itself. The source data come from the DOE CCD, retrieved 2026-09-19. The figure holds only at the test's draw. A household that uses more or less hot water than the test assumes will use a different amount of electricity, and that amount is not available in this data.

Among the 426 models registered as an electric tank at the medium draw pattern, this unit ranks 213th lowest for energy use. That places it in the second-lowest quarter of its class. Its 3,531 kWh equals the class median of 3,531 kWh, so the difference is 0 kWh. Energy use alone therefore does not separate this model from the middle of its class. The listing also gives a first hour rating, the gallons of hot water available in the first hour from a full tank, of 64 gallons, and a rated volume of 37 gallons. Both describe capacity, not energy use. To compare units by fuel, space and size, use the water heater selector.

The running cost is not stated in the text because it depends on the electricity tariff at the reader's own address. The cost calculator applies the rate for your ZIP to the 3,531 kWh shown here, which is valid only at the medium draw pattern. The page explaining how the annual cost is calculated sets out the method. No running-cost estimate is given here, because none can be made without a rate. The modeled installed-cost range appears in its own block with its source and date, and it is not repeated in this text.