The term "Sealed firebox" kinda of a marketing ploy back in the day as opposed to a traditional fireplace with a open hearth. Sealed fire boxes - not sealed in the sense that you control all the intakes or that you can completely shut down all combustion air. Main air intake, secondary air intake, air wash intakes for the window. All have control on main air intake some just switch it to the secondary some have control on both main and secondary none have control on air wash- depending on where it is sourced from. Englander-NC30 has 2 small air intakes behind front legs - air wash i think not controlled, secondary intake on back - not controlled, main air intake on back controlled. adaptable to outside air feed. Nc30 is a good heating unit without the megadollar cost made here in the states. Drolet ( SBI Canada) is another similar line no frills also. I am very happy with my 30.
I melted the thin airwash deflector plate on mine. It sagged down in the middle but I bent it back up with proper bending tools and it still looks pretty good. I never burn unattended and stove top temps never got too hot, all paint is like new. Still runs great just be careful about warming it up at full throttle.
