Right, an 8.5 KG swap n go bottle of LPG yields 116 kWh (cross checked on various sites such as Elgas)

My urn is 2.2 kW so for a one hour boil will use 2.2 kWh, but of course it takes half an hour to get to boiling, so let's say 3.5 kWh to be fair.

So if I switched to gas I should expect to get 116 / 3.5 boils out of a swap n go.

Thus about 36 boils out of a cylinder.

However I hear stories about guys only getting a few boils out of a cylinder, is that right? No intention of going Rambo burner or anything but somewhat surprised. How many boils do the gas men actually get?