Gas burner Advice (Propane or Butane)

[johnnyboy1965]

As you don't have a spare you are going to find out the empty weight eventually then next time you use one from full you will roughly know the amount of brews you have left, TBH i would not run the risk of running out and would have a small spare as backup.

A small back up is ideal. If not, just make sure your supplier is open that day.
I tend to wait until Ive got 1/2 ltr left and then replace. This 1/2ltr left, I just boil up a load of water and use it for deep cleaning my equipment or washing the car or more often sanitising bottles. Thats in the wrong order...Iuse this boiling water to sanitise bottles and then was the car with it.

 

[johnnyboy1965]

I see, though most of the weight would be in bottle itself so you'd need to know empty weight and full weight before you start

Correct, when you but a bottle, ask to weigh a empty one, the supplier will know exactly why. They will probably know the exact weight of a empty bottle anyway.
You can also buy a inline gauge that will tell you how much is left or how much "burn time" is left.

 

[GHW]

I typically do 12-15L

I couldn't do that volume on my shyte electric cooker so no comparison.

If I use hot tap water I can get 20L to strike in 20 mins and the resulting sweet wort to a boil in about the same.

 

[Richie_asg1]

Propane burns hotter, and it has a higher tank pressure. It also works to lower temperatures as you have found out. Burners made for propane will have smaller nozzles and you would need a different set of jets or burner for propane and butane or you will get giant flames out of it unless you can adjust the pressure. Likewise if you put butane into a burner made for propane you may think it is a bit low powered.
Best efficiency is blue flames only as all the fuel is being burned. You shouldn't get soot, only an oily brown residue.

If you are boiling outside then you need a windbreak but make sure that the gas pipe is protected from this reflected heat. Many larger burners have longer supply pipes with this in mind.