At my local Academy sports they sell the 160K for less thgan the 80..TWENTY BUX!!http://www.academy.com/index.php?page=content&target=products/recreation/grilling/fryers&start=0&selectedSKU=0267-40037-0002
anything over 90KI BTU will work.
I live in Louisiana-5 miles from Metal Fusion who are the big maker (under many brand names)of "Cajun" and Bayou" etc burners and even at their rare "damaged"goods sale they aren't this cheap
..have U considerd an electric heat stick?...the energy can be contained with insulation and not wasted as in propane and U can get to 190 degrees easily-EASY to build.Above 210 degrees requires HUGE energy to convert liquid to steam
IMHO,I would ditch the low BTU burner and for 20-30 bux get the 160K and heat 1st water with it then use electric for subsequent water.The problem with storing hot water for future use is that >180 plastic used in coolers WILL leach.I don't know your finances but U could buy TWO for 20 bux each
Re:efficiency-I made a metal shroud for liquor tank as well as boiler whose sides I wrap with a blanket while boiling and always keep the flame within the circumference of the pot...having flames lick the pot is wasteful and NOT any quicker