That appears to be a steam vent using a fin radiator. Is there one pipe or two pipes connected to the radiator?

I have never seen a stream system using a fin radiator. Do you know if this is the original radiator or is it a retrofit?

If the vent is adjustable then trying turning it counterclockwise. If that doesn't work then the vent may need to be replaced.

1 pipe at the ends and 3 that run across the vents. additional pictures below.

unsure on if original or retrofit, but assuming original from the 1950s.

I was under the impression it was a hot water loop.

It's a piece of sheet metal that lays flat on top of the fins when closed. A chain mechanism is used to raise it up on edge to allow airflow. Do you have the fronts of the convector cabinets?

Did you try bleeding the radiator? I am curious how this radiator works.

How would you bleed this type of steam radiator?

Turn the screw on the silver valve on the left.

Helping two years after? lol

yeah, that was definitely came out of the woodwork

HU-12654535, I thought this was a hot water radiator, not steam. And, what Chris said is correct. Let the air come out until water comes, then shut off the screw.

Hello ... I just read this blog. I have the same radiators in my bedrooms. Is there a way to replace these units? I also don't want to used baseboards. What unit can I use to replace these? Should I use a cast Iron radiator ?

It is possible to replace your radiators. Take a look at Runtal Radiators for ideas. You can use cast iron radiators if you have an old house and want to keep that look. There are places which specialize in refurbishing and selling old cast iron radiators.