Good grief -- how big is your tank?! We have a 325 gallon tank, and they estimate it'll run the house for 3-4 days, depending on usage, maybe 5 days if we're really conservative. Or is your house fairly small?
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.