Dunham steam traps

Those are not Burnham traps they are Dunham traps.

There is a variation in the amount of condensate between different manufacturers of steam traps.

For instance a 3/4" Hoffman will do 390lb/hr

3/4" Sarco 279lb/hr

3/4" Watson McDaniel 340lb/hr

But traps are supposed to be selected with a "safety factor"

But in your case I am assuming this is residential or an apartment building then any F & T trap will probably be within the capacity you need if he sticks with the same pipe size of the original traps.

Here are the specs for the old Dunham 30 series F&T traps from page 10 of the Dunham General Products Bulletin of Low-Pressure Steam Heating Appliances, which you can find here:

Dunham General Products Bulletin of Low-Pressure Steam Heating Appliances

I don't think you'll go wrong with Mepco traps; when C. A. Dunham ceased operations, Mepco took over the manufacture of all the Dunham steam traps, so in that regard Dunham = Mepco (compare the above with the attached Mepco 30 brochure). That said, unless I'm mistaken, the smallest 30 series trap they currently make is the 30-7, which is an 1-1/2" trap, so your contractor should substitute the Mepco 44-2 (3/4") H-pattern trap instead. Don't let him sell you a 30-7 and bush it down, either. A 30-7 is way OVERSIZE and probably costs more than 4x the price of a 44-2. The 44-2, being an H-pattern trap, is also much easier to service; all of the guts come out attached to the face-plate and you just change it as an assembly, without having to touch any of the pipes.