If you burn hydrocarbons indoors it will make some carbon monoxide. That can be dangerous in an unventilated area. Most homes aren’t all that air tight. Also, you typically won’t be using a butane burner for very long, and butane burns pretty clean. Use your best judgment for your situation.
I’m posting here now, and then this will likely spill over into ‘annoyed thoughts’ as we go. I’ve taken the subfloor out of the bathroom, we are down to the joists now - I have a little left to remove but it’s almost done. The plumbers start this week roughing in the drains, framing is next week, then more plumbing and electrical the following week. Finally seeing some light at the end of this tunnel, it’s been a doozy.
Plumbers found a drain that’s failing - one we were not planning to replace. That doesn’t sound like a happy thought, but it’ll be like $100 to fix and they caught it before it caused any damage.