Why is my radiator hissing?

Question

I've never had a radiator before, all central air for me, but I'm living in an apartment that has them now. All of the radiators in my apartment have been hissing, and pouring out steam from the "valve" on the side. I'm not sure what the "valve" is or even if it's a valve, but it seems to relieve pressure and it's not always on when the radiator is so I'm guessing there is an 'on' and 'off' position. Here is a a wikipedia picture of one that has the same type of "valve":

My questions are as follows:

• Should it be hissing? (it's really loud)

• Is there anything I can do to make it quieter?

• If there isn't, would an unorthodox solution, such as putting something that allows air through over the "valve" be safe? I've used a wet sponge for short periods when it really annoys me.

Answer 1

This is basically going to be landlord work unless you plan playing heating technician and checking the basement pipes. Here's the gist:

• Air vents on the radiator must flow air out so it can be replaced by steam to heat. They sometimes have adjustment valves on them so you can balance the system.
• Air vents that are producing a lot of noise are either
  • too small of a vent
  • clogged up / broken (this is you because you're leaking steam)
• Improperly designed systems can also push a lot of air out of the radiators. The steam delivery pipes should also have air vents on them before the radiators.

When working properly, those air valves should not let steam through. They should close when the steam reaches them, and open when there isn't steam. If there are showing visible steam, they need replacement.

I found this to be a good article on caring for steam vents that will provide more detail.