if you don't have an expensive cooler, keeping a burbot in an aquarium makes no sense...
30 degrees of celsius in the house during the summer is too much for a cold water aquarium with burbot.
That's probably correct...if your house is kept at 30C, which few are, at least here in North America. Blanket statements like that...make no sense...
I am one of the few folks who don't even have AC in my home; I live a couple hours north of the US/Canada border, but even here we may have 30C+ daytime temperatures for a few weeks each summer. And yet, most folks have AC, despite the fact that it is only used for a relatively brief period each year.
Even when I lived in Ontario, much further south than I do now, there were many years when I simply never used my home's central air conditioning.
I've been monitoring the temps in the basement tank in which my burbot was kept last spring; throughout the summer it has never exceeded 20C (68F) and was usually at least 4 degrees cooler than that. Based upon how the fish acted I don't think it would have experienced any issues, and the post above by
@Inland Aquatics seems to confirm that. If necessary, a tank could be placed directly upon the concrete floor in my basement; the floor temp has never once exceeded 60F (under 16F).
It does indeed make no sense to keep a fish if you know you cannot provide the conditions it requires, whether that refers to tank size, temperature, water chemistry, etc...but there's no need to frighten away potential keepers who have the proper conditions available.