In this video, Paul Bruneau installed a sight glass on his steam boiler's riser to see the quality of steam it produces.
Dry steam is the good stuff. “Wet” steam is steam that contains more than 2% water. It’s the bad stuff because the water uses up a good portion of the steam’s latent heat before it can get out into the piping. When that happens, the building suffers. The steam dies in the header and the near-boiler piping. The people freeze.
Your steam-heating system can produce wet steam if it has improper piping or water level.
Here are some ways to avoid wet steam.
In this situation, Paul lowered the water line about an inch and the result was much dryer steam: