Is it normal to have rust in brand new firebox?

It looks like surface rust and shouldn't be a problem.

Agreed, just surface rust, no problem. That's thick steel, and won't be subjected to any additional moisture unless water comes down the liner/chimney.
My SIL's had a little rust there. They left it outside when they took it off the truck, and it got rained on a little bit before I got there to pick it up. Even though it was wrapped in plastic, a little water found its way through. Everything else in the top of the stove, the baffle and the rails, are stainless.

It's untreated steel, mearley humidity will do that to an area with less oils on it. See what that looks like after a year of fires. It's fine.

Starting out like that or starting out absolutely rust-free, it is going to look the same (black and rusty) next year at this time. Don't sweat it.

You can wire brush it if it really bothers you, but it'd be a waste of time

Neil Young says "Rust Never Sleeps", and your T5 is not exempt.


It will soon be unrecognizable as being black metal. (meaning, covered in soot and char). Don't worry about it.