Calculation of Energy Consumption

There are four categories of end-uses where energy consumption is estimated; heating & cooling, water heating, appliances (including misc plug loads), and lighting. The Home Energy Saver uses engineering models to estimate energy consumption for all these end-uses.

The legacy energy calculation methods used by the Home Energy Saver API are located here.

For both the “quick inputs” and “detailed inputs” levels, the models used to estimate energy consumption are identical, with user-entered values substituting for default values as the user progresses through the “detailed inputs” level.

The Home Energy Saver utilizes data from a variety of sources to provide default input values and energy consumption. The bulk of the data compilation for the Home Energy Saver was completed in 1997-1999, and the most current data available at that time was used. For time-sensitive series such as equipment efficiencies and state energy prices, the data are updated to the most current data available on an annual basis.

Major End-Use

Quick Inputs Level

Detailed Inputs Level

Heating and Cooling

City with similar climate

House construction year

Conditioned floor area

Stories above ground level


Foundation type

Ceiling/floor/wall insulation

Heating/cooling equipment

Window area (each side of house)

Number of occupants in age groups (also affects water heating)

Approximately 80 additional questions about house shape & size; exterior shading; air-tightness; foundation & floor; walls; doors & windows; skylights; attic & roof; ducts & boiler pipes; thermostat details; heating & cooling equipment (efficiency, vintage, etc.)

Water Heating

Water heater fuel

Eight additional questions about temperature settings, water heater location and specifics, etc.

Major Appliances

Number of refrigerators (1-3)

Number of freezers (0-2)

Presence of clothes washer

Specific details about the refrigerators and freezers specified in the simple level; 8 questions about cooking and your dishwasher; 5 questions about clothes washers/dryers; 8 questions about hot tubs, spas and pumps


No questions

Two levels – 1st asks for the number of fixtures/room, energy consumption/fixture defaulted based on TPU study, 2nd asks for detains on the number of bulbs, bulb type, total wattage and usage for each fixture.

Small Appliances

No questions

Roughly 50 questions about entertainment, home office, misc. kitchen appliances and other appliances.