I have a 7200k Kohler 8 gallon tank. Luckily, I've only used it 3 times in the 6 years I've owned it. The owenr's Manual says it should go 11 hrs at 1/2 duty. One time in summer with 2 a/c units, the fridge, TV and 5 house lights on it went 12 hrs with at least a gallon left. The other two times were winter with pellet stove, fridge, tvs, boiler for hot water, and house lights it went 15 and 16 hrs till empty. It idled most of that time and would only ramp up when microwave was used or two appliances where on at once. I think I could stretch it a bit further if I only used it as needed instead of just letting it go.