Low Range Pressure Transmitter

Both gauge and differential pressure transmitters compare the measured pressure to a reference pressure.

A gauge pressure transmitter references atmosphere, typically through a vent somewhere, there's no separate port for the atmospheric reference. A differential pressure transmitter provides a port for each measurement.

Your application is for a dual port differential instrument: a room pressure measurement with respect to outside-the-room-pressure.

You cannot do it with two gauge pressure measurements; one inside the room, one outside the room. Both will just show 0 pressure, because gauge pressure references its immediate surrounding environment. There's no difference between an elevated room pressure and elevated room pressure. They're both the same. The difference of two identical values (gauge pressure port minus exterior environment pressure) is zero.

I've seen people hard pipe an impulse tube into a safe area. There's no flow, it's dead headed.

There are industrial DP transmitters or smaller non-industrial panel mount units that are designed for pharma or clean room use that make measurements in this range; United Electric LPS, Sensocon, Dwyer, to name a few.

The industrials could be mounted in the hazardous area and wired as EXP or I/S for a hazardous area if piping into a non-hazardous area is too much to deal with.