I will be installing electric baseboard heat in an attic/playroom conversion. 3 sections for 4500 watts (which equals 18.75 amps @ 240 v.)
424.3(B) requires 125% for branch circuit conductors and OCPDs. This comes to 23.4 amps. I plan to run a 30 amp circuit and I want to install a line voltage t-stat as opposed to low voltage relaying.
The problem is I can't locate a t-stat rated above 22 amps. This will handle the 18.75 amp load but I'm not sure if the t-stat is also required to be rated @ 125%. (23.4 amps)
Help, anyone?

I would treat the t-stat like any other switch. See 380-14(a). The 22Amp t-stat is good for the 18.75Amp load. The wiring is sized no more than 80% so there will not be any heat buildup at the terminal screws, and there is no service factor, like in motors, to worry about with the resistive load.