Hi
If you *really* got 170K BTU's, you would go through a normal tank of propane in no time at all. You also likely would have the tank ice up on you even in the middle of summer. 50K "real" BTU's is plenty for any normal (sub 30 gallon) setup.
Some math:
170K BTU's / 21,000 = 8 lb of propane an hour. A normal tank is 20 pounds. You would get about 2 1/2 hours on a tank.
20 gallons of water weigh 160 pounds. A BTU heats a pound of water one degree F. 170,000 BTU's would heat your kettle 1,000 degrees in an hour. Actually since boiling takes a lot more energy, that's not what would happen. You would get to boiling from room in under 10 minutes.
Bob