OP poster could run the torch flat out from full tank to empty, and
note the time.

or store a spare tank under a overturned garbage can. i did that years
ago with some spare gasoline

or build a ventilated secure container of some sort close to the house
for easy tank swap.

while OP is concerned about weight of tank, he may not realize the
weighing unit and scale will make moving the unit heavier.......

if OP concrete areas need replaced i would suggest a new whatever with
imbeded PEX line to warm the areas when needed