Hey bud,
I just picked up a med pressure Rambo burner as my 3 ring can struggle at times in the open air due to wind disturbance and im sick of the inconsistency as i brew outside 9/10 times.
When i was living at my folks place, i woudl use it in their garage with the door adjar and window open for air circulation. It would get to a rolling boil and hold just fine and could be kept at a rolling boil in winter with the inner ring turned off. In summer it usually requires all three rings on at once. Im assuming due to the condensing of air in winter it fires better. Either way, if you want to use a burner 'indoors', a 3 ring cast iron job is fine.
$50 bucks and its yours. Burner+Reg.