A year's supply! Either you've got a very big tank, or you're extremely frugal/well insulated. Keep an eye on the telemetry numbers and order when you get to 2!

You do have a little digital readout gizmo in the house that wirelessly knows the fullness of the tank, don't you?

But that's the madness of it John. The digital read-out is at the gas suppliers. They know exactly how much fuel I've got. Whereas I have to burrow into the undergrowth with a special key and a torch. Anyway, next time they've promised to deliver some fuel before I run out. Oh and my tank holds 1250 litres of propane which is a bit above the average annual usage for my house.