500 gallons, which I keep full at all times. I have not used it for more than 5 days. It used about 60 gallons during that time, but could vary drastically depending on how and when you use it. However, it is just two of us adults, so we don’t use that much electricity, and the design of the system is zoned. So you can restrict the usage to essential systems, which we do during blackouts. In other words, you don’t need A/C, etc., during certain times of the year, and under duress, you can ration if needed. Our system has 6 zones, and it is programmed automatically to shut off systems as needed.
Well, that gives me a little hope they underestimated how long our tank will last. It’s just the two of us as well, and even though we work at home our typical electric usage is pretty good.
In any case, the longest we’ve ever gone without power — in my life — was 5 days, when a derecho swept through Central Virginia. The Generac should easily get us through most situations.
When we ordered our generator, our needs were sized to be about 15 kW with everything running. The generator output was rated at 20 kW, so we had some margin. Then Briggs & Stratton did some mods to the model we ordered after we ordered it (during COVID) and it was up-rated to 26 kW. I purchased two “Load Shed Modules” which take the oven and AC off line while the generator starts. After the generator has started and is running, it sequentially turns those loads on. This approach assures that all the loads don’t start at once which would trip the generator back offline causing a restart / shutdown / restart endless loop.