How we test
We don’t run hands-on tests. Every number on this site comes from a published source we can link to: government test data, manufacturer spec sheets and manuals, and utility sizing charts. This page explains which source we use for what, and how the calculator turns those numbers into runtimes.
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What we don’t do
We don’t own test units, and we don’t put appliances on a power meter. When a page shows how long a battery runs something, we calculated it from published figures. If we ever publish our own measurement, the page will say so and explain how we took it.
Two kinds of appliance numbers
Sources measure two different things, and the wattage pages show both.
Sizing watts are the running and startup watts used to choose a generator or inverter. They come from generator sizing sheets published by EWEB (the public utility in Eugene, Oregon), Generac and Amana, and from manufacturer spec sheets such as Franklin Electric for well pumps, Zoeller for sump pumps and ResMed and Philips for CPAP machines. These figures are generous on purpose, so a generator sized with them won’t stall.
Measured draw comes from ENERGY STAR’s lists of certified models and their test results. For fridges and freezers that means the average across a whole day, which is the number that decides how long a battery lasts. For window air conditioners, dehumidifiers and TVs it means what certified models draw while they run.
The gap between the two can be large. Sizing sheets put a refrigerator at 700 to 1,000 running watts. Across 2,987 full-size models in the ENERGY STAR data, the average over 24 hours is 52 watts.
How we use ENERGY STAR data
We download the certified product lists and group models by type and size. For each group we report the median and the range from the 10th to the 90th percentile, so one unusual model doesn’t skew the figure. Each wattage page says how many models a figure covers. The math runs as a script, so we can refresh the figures when ENERGY STAR updates its lists.
When sources disagree or are missing
When two good sources give different numbers, we show the range and name both. When the only source we have is a retailer page or an older study, the page says so. If we can’t find a source for a figure, we leave it out and say it’s missing.
How the runtime calculator works
The runtime calculator uses the same data. Each appliance uses its watts for the hours a day you give it. Fridges and freezers use the yearly kWh on their EnergyGuide label instead, because they cycle on and off by themselves.
Runtime is the battery’s rated capacity times 85%, to allow for inverter losses, divided by the average draw. The peak load is everything switched on plus the biggest single startup surge, the same method EWEB’s sizing sheet uses. Your own appliances will draw more or less than these averages, so treat the results as estimates and check them against the labels on your equipment.
Product specs
When we compare power stations, generators or home batteries, capacity, output and other specs come from the manufacturer’s spec sheet or manual, and we link to it. Those are the maker’s claims, and we label them that way.
Safety information
Safety statements cite the CPSC, NFPA, CDC, Ready.gov, USDA or the equipment manufacturer’s manual. A safety page that hasn’t been reviewed by a licensed electrician or another qualified reviewer carries a note at the top until it is. The editorial policy has more on sources and corrections.