The Home Energy Saver: Comparing Your Results to Your Utility Bill

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Comparing Your Results to Your Utility Bill

Energy use varies widely, even among seemingly identical homes! This is because of differences in house design, appliances, lifestyles, and comfort requirements. If your Home Energy Saver results differ from your actual energy bills, be sure to first check that all your input values agree with how your home is actually designed and operated. If the total cost differs but energy use is the same, keep in mind that we use a single price for energy, while many utilities use complicated "tariff structures", where the price varies by the time of year and/or day, your level of consumption, or other factors. Any remaining differences are probably due to one or more of the factors below. After reviewing these factors, you may want to modify some of the HES inputs that are more difficult to measure or estimate (thermostats settings, washer loads, insulation levels, percent of floor area that is conditioned) to get a better match between your actual bills and the HES estimates.

Following are factors that could cause your actual consumption to be higher than the HES results. Most can be corrected by double-checking and modifying your house description.

you have miscellaneous appliances not included in the HES input pages
you have more than one refrigerator or other major energy user that you forgot to input into HES
you use portable space heaters during the winter, but did not include them in your house description
your ducts are leakier and/or less insulated than specified
your insulation was not properly installed or has deteriorated over time
your appliances, spa, pool, or other miscellaneous appliances are larger, less efficient, or operated more than HES assumes
you keep your thermostat on higher settings than modeled in HES (remember that thermostat settings can be very complicated if different household members use different settings)
last winter (or the period that your actual bills are from) was colder than average, and/or the summer was hotter than average*
you had extra visitors (remember those pesky in-laws that came in August... and stayed through Thanksgiving?)

Following are factors that could cause your actual consumption to be lower than the HES results. Most can be corrected by double-checking and modifying your house description.

you have a wood stove or solar heating, whose energy cost is not included in your utility bills
you don't heat or cool parts of your house that were included in the HES inputs
you use a clothesline instead of a clothes dryer
you took a long vacation this year
your appliances, spa, pool, or other miscellaneous appliances smaller, more efficient, or are operated less than HES assumes
you keep your thermostat on lower settings than modeled in HES (remember that thermostat settings can be very complicated if different household members use different settings)
last winter (or the period that your actual bills are from) was warmer than average, and/or the summer was cooler than average*

* Keep in mind that the Home Energy Saver estimates heating and cooling usage assuming 30-year average climatic conditions between 1961 and 1990. The climate in any given year is going to differ somewhat from this average (usually by less than +/-20%). To get a sense for how the climate from the period of your actual bills compares to the long-term average climate, you can look at the data available on-line either at the State or Regional Climate Centers, (general climate data is available from National Climate Data Center).